Recognize and Fix Faults in Notebook

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Preface Repairing PCs in general and notebooks in particular, is a job that requires certain equipment and knowledge, at least when repair is meant to go to “put” hands on electronic boards. In fact, if you replace a hard drive or an optical disc player operation is feasible as long as most of the technical know how to recognize a free IDE and S- ATA and know the capacity limit of addressable by a BIOS , even going to replace a TFT LCD panel with a compatible or change a TFT LCD panel with backlight lamp with a LED backlit, requires that something extra. The speech takes on more significance when you have to go looking for a fault in a video card, power supply, or the motherboard of the notebook, where the complexity of today’s technologies, aimed at containing increasing size while increasing performance, makes the task the technical increasingly difficult, also because of the limited availability of wiring diagrams that describe the electronic circuitry of the computer. This book was born from reparation lab of www.riparazione-notebook.net and starts with some knowledge of electronics, which represent the basic preparation for a technician who is not released from a technical institute to e-mail address or by a faculty of electrical Engineering, must have to understand how to deal with failures electrical / electronic, act with changes when it is not possible to repair/find an original member, go to the troubleshooting without having detailed schematic diagrams. There is a large section that describes the basic structure of a notebook computer and an overview of those failures in laptops that have become characteristic of the last decade, where the integration thrust and the increase in computing performance and graphics (not followed by an increase of the space and the size of the cooling systems) have brought to market computer beautiful to look at and practical to carry, but of short duration and exposed to frequent problems such as the posting of some pads of the chip more thermally stressed GPU and chipsets, especially the Northbridge. A special chapter is devoted to the techniques of rewelding and reflow of these chips, which represent the first approach, and the replacement of SMD and BGA chips, which are the extreme solution when the reflow fails. No less importance is given to the identification and repair of power supply faults, topic today is not negligible because the motherboard of a notebook, there are several stages of DC/DC converter specifically dedicated to supply the chipset, the I

CPU, the RAM, the audio stages and card readers (and more): just go to one of the main fault, and the notebook will not turn on anymore, making it difficult to understand the origin of the problem. We also address the failures of input devices such as keyboard and touchpad and replacement of interface chip, called the Multifunction Keyboard Encoder or Super I/O, as well as the anomalies in audio sections and units of mass storage. For practical reasons this volume, constantly changing, it can not address all the circumstances, as each computer has its own structure, which while similar to that of many others, has particularities in times such as to make it behave in a manner quite different. But it is, we believe, a guidance and a solid foundation on which to build, with the experience,

competence and ability to address and resolve faults, from simple to complex. Have a good reading. The staff of Riparazione Notebook.net II

Copyright © 2012 CoreTech Srl Viale Ortles 13, Milano (MI) Email: [email protected] Web: www.riparazione-notebook.net www.ricambi-notebook.net The information contained in this book have been tested and documented with the greatest possible care. No liability resulting from its use can be attributed to the author and CoreTech Srl or any person or company involved in the creation, production and distribution of this book. All rights are reserved by law and in accordance with international conventions. No part of this book may be reproduced by means of electronic, mechanical or other means, without the written permission of CoreTech Ltd. III IV

Summary CAPITOLO 1 - BASIC OF ELECTRONICS……………………………………………………………….1 CAPITOLO 2 - PASSIVE ELECTRONIC COMPONENTS………………………………………….19 CAPITOLO 3 - ACTIVE ELECTRONIC COMPONENTS …………………………………………..39 CAPITOLO 4 - INTEGRATED CIRCUITS………………………………………………………………..57 CAPITOLO 5 - PC MONITORS…………………………………………………………………………..69 CAPITOLO 6 - DC/DC POWER SUPPLIES…………………………………………………………….87 CAPITOLO 7 - NOTEBOOK STRUCTURE……………………………………………………………105 CAPITOLO 8 - EQUIP ITSELF TO RAPAIR NOTEBOOKS………………………………………145 CAPITOLO 9 - FAULTS ON POWER SUPPLY……………………………………………………….181 CAPITOLO 10 - VIDEO FAULTS………………………………………………………………………….195 CAPITOLO 11 - FAULTS IN CPU, RAM, BIOS AND CHIPSET………………………………….223 CAPITOLO 12 - FAULTS IN MEMORY MASS UNITS………………………………………….235 CAPITOLO 13 - FAULTS IN COMMUNICATION PORTS…………………………………………243 CAPITOLO 14 - FAULTS ON COOLING SYSTEM………………………………………………….249 CAPITOLO 15 - FAULTS OF KEYBOARD & TOUCHPAD……………………………………….255 CAPITOLO 16 - AUDIO FAULTS………………………………………………………………………….261 V

www.riparazione-notebook.net CHAPTER 1 BASIC OF ELECTRONICS Before learning what is a notebook and how does it works, you need to have a little knowhow about electronics and its fundamental concepts, otherwise we cannot understand how the circuits that make up the computer, let alone assess whether a certain stage works well or less how and with what to replace a certain component. The purpose of this chapter is to provide the basics, starting from the assumption that there is no electricity at the base of the electronics, which is the set of all the phenomena related to the release or movement of electrons, the latter being infinitely small particles that, along with protons and neutrons, make up atoms, which are the “building blocks” that make up everything around us. When, for particular physical conditions, one of the electrons is lost, it creates an imbalance of charge and electrical phenomena arise, which can be: statics , in which case we speak of electrostatic, i.e. presence of electric charge on a body, due to missing or extra electrons, but which will remain static; dynamics, the outer electrons of the atom move from one atom to another and talk, then, of electric current. For the operation of any electronic apparatus have relevance primarily the latter, however, not be neglected static phenomena, given that, for example, the accumulation of static electricity may be responsible for the damage of some particularly delicate components of the notebook and generally those MOS technology, for this should be avoided or contained. Now, we consider only the electric current, which is a movement of electrons from one atom to another, or even in a vacuum. Just in terms of how they behave with respect to the current, the materials can be divided into: conductors, are crossed through by the current; semiconductor are made by cross current but only under certain conditions (typically, depending on the polarity); insulation, do not let through by the current. The electric current arises typically in conductors or semiconductors, but can flow in the insulating too by breaking their chemical structure through the application of an understanding energy (breakdown) which, however, damages the insulation. The conductors are metal and have a chemistry which sees the outermost electrons very weakly bound to the nucleus. This allows, by applying a slight electric field, to tear from the atom to which they belong, making them pass from one atom to another and creating the electrical current. The flow goes from one end of the conductive material, when the applied electric field has a certain polarity. For electric field includes the densification of forced negative electrical charges of the one part and of atoms with a positive charge discovery; what determines what we call the voltage, or potential difference. Electronics is the discipline that studies the current in the semiconductor and into the void. One important thing to say is that the current propagates with an effort, then the movement of electrons required by the voltage generator some work and continued supply of energy. The difficulty encountered by the generator in pushing the electrons is named electrical

resistance; each material has a resistance, which depends on how it impedes the propagation of electrons.

The origin of the electrical current The current arises in devices and components which, therefore, are called generators, which can be current generators or voltage generators. Indeed it is just a way to see the same thing in two respects, since when it generates a potential difference between two points, closing them with a user determines the flow of current. The voltage generator produces, therefore, also the current and the current is always consequence of the existence of an electrical voltage or potential difference, if you prefer. Wanting to go into details, we must say that a voltage generator produces a pure constant potential difference and the current that can deliver depends on the resistance of the user that there is connected, a current generator, however, regardless of the resistance of the user tends to always maintain the same current value. Summing up, the voltage generator determines a voltage drop across its heads, that we can measure in volts (V); may produce DC voltage or variable voltage. The current generator induces, in the circuit connected to its heads, an electric current expressed in amperes (A). The current produced can be continuous or This applies to ideal (theoretical) generators, who exist only in theory, but in practice any electric machine (alternator or dynamo) or circuit (power supply) is suffering from a parasitic resistance, which in the real voltage source is in series to the terminals, while in the real power is located in parallel. The resistance of the voltage generator, being in series with the circuit that feeds it, limiting the voltage provided in a manner directly proportional to the output current, or requested by the user. The resistance in parallel to the current generator subtracts (shunt) part of the current generated and decreases that delivered to the user. Figure 1.1 shows the graphic symbols of the generators of voltage and current theoretical (ideal). In real world, the electric current can be generated with the electrical machines such as alternators (AC generators) and dynamo or other systems such as photovoltaic panels and the batteries of various kinds (electrochemical, thermal power stations etc..). In electronic power supply is used: this equipment is not a generator itself, but simply draws voltage and current from the power line to 220 V or from other lines; the power supply is a kind of ideal voltage generator having a certain resistance in series with the output that makes it lower, to a certain extent, the output voltage, as a function of the output current. Therefore, the power supply has an input, from which it receives the starting voltage and all the current that is necessary, and an output, which powers the load (the element that absorbs the energy of the generator).

The electric power When we speak of power in a circuit, an electric load or a generator, it means the energy consumed per unit of time; more simply, the electrical power is the product of voltage by current. Electric power is explained by equation: P = V x I If we speak about a generator or a power supply, the voltage that is present at the output

and the current that flows due to it; speaking, in this case, the power generated or delivered. When, instead, it refers to a user (for example a resistance) is the power dissipated or consumed, the voltage is the one received from the load and the current flowing to the effect of the applied voltage.

www.riparazione-notebook.net Graphic symbol used in electric engineering to indicate voltage generator (on the left) and current generator (on the right). 3

Fundamental laws of electrical engineering Before knowing the components and electronic circuits, one must know the main laws that regulate the electrical current; these are Ohm’s Law and Kirchhof ’s principles. Ohm’s Law The first rule to learn is Ohm’s Law, which says that a resistor, that is a conductor, which by its nature opposes a certain resistance to the passage of electricity, there is a drop or loss of voltage that depends on the ‘current intensity (I) according to the report (Figure 1.2): D V = I x R where R is the one that is defined in electrical electrical resistance, which is measured in ohms, while D V is the voltage drop. Reasoning analogously, we can say that in a resistance subjected to a potential difference of a current flow equal to: D I = V / R Ohm’s law allows, for example, to determine the loss of a generator in his own real internal resistance Ro, so, in a voltage generator (the typical stabilized power supply or not) the withdrawable voltage (Vu) is equal to: Vu Vo = - (x Iu Ro) Iu where Vo is the output current and the open circuit voltage (Figure 1.3). Regarding the current generator, the generated voltage (Vu) depends on the resistance, according to the formula: Vu = I x Ro Where I is the current own generator. The loss of current (Ip) derived from the internal resistance Ro (located in parallel) is equal to: Ip = I - (Vu / Ro)

Current flows trough a resistor, a wire or a lane of a PCB, causes a voltage

drop across the

Figure 1.3 Real voltage (left) and current (right) generators with their parasitic resistors who means internal power loss of generators.

Kirchhoff’s principles Two other fundamental laws of electrical engineering, explaining how electricity grids operate, ie sets of generators and electrical or electronic components, are the principles of Kirchhoff: the first is the principle applied to the nodes and the second one through the net. Before you say them, you have to define nodes and links: node is called a point of union of two branches (a branch office is a part of a single circuit current) ie wires or terminals of components or generators are characterized by the fact that two sliding different currents, for example, two components or wires connected between them carry the same current and the council is not, therefore, a node. When, instead, the two branches merge into one, leaving a third branch that carries the sum of the currents, well, there is created a node (Figure 1.4). The principle of Kirchhoff to the nodes in a node says that the sum of the currents entering must equal that of the outgoing currents, namely that the algebraic sum of the currents must be zero. With reference to Figure 1.4, the current Iu call outgoing from the node and the sink currents I1 and I2, the following relationship applies: Iu = I1 + I2 As to the second principle of Kirchhoff, we must say that a mesh is a closed electrical circuit of a generator (Figure 1.5), well, the principle applied to the mesh says that in a mesh the algebraic sum of the voltage drops and the potential differences generated must be zero:

www.riparazione-notebook.net Electrical node: output current is the addiction of the input 5

V - V1 - V2 = 0 or even: V = V1 + V2

DC and AC Figure 1.5 Electrical mesh: generator’s output voltage is equal to voltage drops across resistors.

The electric current can be continuous or variable: in the first case the movement of electrons is constant intensity over time, while in the second the intensity varies in a random or regular; in the latter case, it is said that the current is periodic and for it is possible to define a frequency of variation, expressed in periods per second, or in hertz (Hz). The alternating current is a variable current periodically, where the flow of electrons is reversed cyclically and with it the polarity; unlike the continuous and variable, the alternating assume values both positive and negative. The sine wave (that of the mains voltage) is so named because it reflects the performance of the sine of an angle ranging from 0 to 360 °, which is equal to 0 at 0 °, 90 ° 1, again 0 at 180 °, -1 to 270 ° and, finally, again zero to 360 °. For this reason, since the period of 360 ° and therefore equal to the circumference of a circle (that is 2 times the radius , where worth 3.1416) considering /2 the angle of 90 ° (right angle) to 180 ° (angle plate) and 2 angle turn (360 °). The alternating current (Figure 1.6) is the one that comes out of the mains supply to your home, offices, factories etc.. In european countries is 220÷240 volts in amplitude and 50 Hz frequency. Work with it the power of computers, monitors, televisions, etc.. Also the voltage generated by the LCD of the notebook

www.riparazione-notebook.net Figure 1.6 Graphical representation (waveform) of alterned sinewave in the 220 Vac of home main net. 6

Figure 1.7 Graphical representation of square wave: this waveform is named square when amplitude of a single pulse in each half period is equal to half period (when duration/amplitude is equal to 1). Picture shows a positive, unidirectional square wave. Alterned square wave have values both positive and negative and in graph comes under t axis.

is alternating, although almost always is of rectangular waveform, while that which is produced by the DC / DC power supply of the blocks is continuous pulse, then unidirectional. In America and Japan, for example, the network is at 60 Hz and provides 110 ÷ 120 Vac. At one time, this diversity made the PC import unsuitable for use in Italy, or forced to use transformers or to make provision in the power supply voltage selector, and today the AC/DC notebook are all multi-voltage, meaning they can be adapted to function as a 100 to 240 Vac without difficulty and in a fully automatic way (auto-range).

Static Electricity It is the thickening of electrons in certain areas of materials or the Earth’s atmosphere, due to the fact that, although there is a potential difference, this is not sufficient to ensure that the electrons go to fill gaps in the area where they are lacking, or the electrical circuit is open. Static electricity is comparable to water in a tank raised, who can not get off because its force can not make it to open the drain plug. The electrostatic phenomena are responsible for example of the attraction of the hairs and hair by electrified objects, as well as dust on old vinyl records, on the furniture and on plastic materials, but sometimes also cause currents of great intensity, such as lightning. The electrostatic occurs in the insulating bodies and in the air, but not in the conductors, since if a material conducts electricity, congestive charge is canceled because the electrons can pass through the material forming the electric current. The electrostatic phenomena arise when an insulating material is mechanically stressed or approached by a large amount of electric charge or exposed to a strong electric field induced by a voltage or an electrified body. In the case of mechanical stress, electrostatic phenomena arise because of the piezoelectric effect, consisting in the deformation of the structure of some crystals (quartz) and ceramic materials (barium titanate, for example) that causes the exposure of electrons from one side and of positive findings from the opposite side, but also by rubbing them between two insulating materials with different atomic structure device: in

this case, the outer electrons moving and discover in a positive and another thicken forming negative charge. The situation remains unchanged because, as the insulating materials, the electrons remain stationary. Electrostatic phenomenon is caused when we get up from a chair equipped with plastic wheels with rubber or plastic, after we were seated wearing synthetic or woolen clothes and shoes with rubber soles: getting up, carry around any static electricity and if you touch something metal connected to earth, we take the shock. The same happens even when, going down from the car in a dry and windy day, we take the shock. In the bodies, the electric charge thickens fairly evenly, however, comes off in the vicinity of the contoured areas to tip, or from the ends; this because, for the same electric potential difference, the discharge takes place from the closest point between the two zones otherwise charged (positive and negative). The electrification is not equal for all the materials, but it depends on each of them: some assume positive charge and other negative charge, more exactly, is positively electrify substances such as glass or plexiglass and in those that behave similarly (ie, when rubbed, reject all such materials) and negative ones such as ebonite or that, when rubbed, ebonite repel and attract the glass. The accumulation of charge in our body is important in an electronics laboratory, especially if you fix computers and boards with MOS or CMOS logic, which are now the only ones used in Notebook, because if you touch both sides of a card after Having accumulated static electricity, it may discharge through the circuit board and damaging sensitive components. The same applies if you get up from a chair accumulating electric charge and you touch a part of a card when the computer is connected to the power line or large metal parts. For this reason it is a good rule, during repairs, provide the workbenches to put a metallic bracelet on the wrist of those who must manipulate and weld integrated, electrically connected to the ground with a chain of iron. This allows you to download the electricity that would be formed for the rubbing of clothes and synthetic wool with plastic chairs. Even the tip of the soldering iron should be grounded. The Faraday’s cage In the conductors, electrical charges tend always to be arranged preferably on the outside, or on the surface, and this is responsible for the so-called “skin effect”, which in the cables sees the large part of the current flowing on the surface, a phenomenon which oxidize the cables leads to an increase of losses over time. The fact that electrons tend to be arranged on the outer surface of metals is demonstrated by the Faraday’s cage: investing a metal cage with an electric field, within this nothing happens and any object introduced is not affected by any electrostatic force nor electrifies . This phenomenon is used in the shielding of electronic equipment, such as measuring instruments for weak electrical signals and audio equipment: they are enclosed in metal casings or covered with aluminum foil then connected to ground (or to the ground connection of the electrical system, now mandatory in all settlements) and typically the mass of the circuits, with the foresight to realize the connection of the latter in only one point, otherwise it is possible that create potential differences along the metal of the container, responsible of the invasion of disorders in the circuits themselves.

Magnetism It is a phenomenon that affects mainly metals and which can be defined as the ability of a

material to attract or repel matter similar to himself and that exists in nature since the birth of the world, its most striking manifestation can be seen using a compass, whose needle is attracted to the magnetized north pole. In practice, the magnetism consists in attracting, by a mass of ferromagnetic material, of another also composed of ferromagnetic material. The importance of magnetism lies in the fact that it is based on the operation of the speakers for the display inverter and DC/DC converters internal to a notebook, but also the AC/DC external. For the purposes of the study of magnetism, materials are divided into ferromagnetic, paramagnetic and diamagnetic: the first are those who show strong magnetic activity or who can acquire when exposed to a strong magnetic field, the latter behave similarly to the ferromagnetic, however, have no effect minimum and negligible. The diamagnetic, finally, are insensitive to magnetism and do not interfere with it. Electromagnetism The current flowing in a conductor generates a magnetic field whose intensity is proportional to that of the current itself and, if the latter is variable, the field assumes the same trend; the magnetic field generated by a current-carrying conductor is said “electromagnetic field” and its manifestations go under the name of electromagnetism. The creation of electromagnetic fields by tenants is the cause of the noise radiated by the DC/DC converters of the computer, but also produces many positive effects. The electric current acts on the magnets and interacts with the magnetic fields, however, it is also true that a magnetic field can in turn act on current: more precisely, exerts a force on a conductor path by electricity. This phenomenon allows the operation of the speakers magnetodynamic and electric motors used for example in the floppy-disk and CD/DVD, but also in the HD, to spin the disk and move the heads. The phenomenon can be verified by placing a rectilinear electric wire between the polar expansions (the poles) of a magnet so as to be perpendicular to the field lines, direct from the north pole to the south. Sliding current in the wire, this moves and does orthogonally with respect to the direction of the same current and the magnetic field produced by the magnet. The direction of the shift depends on that of the current, in the sense that if it changes it reverses the polarity of the electricity generator that slides in the cable. In other words, when a conductor through which electricity is to be immersed in a magnetic field exerted on it is a force whose direction is perpendicular to both direct lines from the north pole to the south, and to the direction of the current (Figure 1.8). The direction of the force can be determined with the so-called “left hand rule”: if you have thumb, index and middle finger in order to keep them perpendicular to each other, if the average indicates the current direction and that the index of the field lines magnetic, the force exerted on the conductor (represented by the middle finger) is directed as indicated by the thumb (Figure 1.9). The force exerted by a magnetic field is directly proportional to the current flowing through the conductor itself, the length of the portion of the latter which is located in the magnetic field and to the sine of the angle formed by the direction of the lines of force of the field with that of the conductor. All this can be represented by the following formula: F = B x I x l x sin where F is the force exerted on the conductor path from the current of intensity equal to I and whose length is l, while a is the angle formed by the field lines with the conductor itself. B is the magnetic induction, ie a vector whose magnitude is represented by the usual

formula when the angle a is 1. Magnetic field induced by the current The magnetic effect due to electric currents is extremely important because it allows you to accomplish such as electric motors, systems for identifying objects using RFID, the detectors, radio etc.. The intensity of the magnetic induction in a considered point of the field produced by a conductor path of electric current is directly proportional to the intensity of the current itself and inversely to the distance from the conductor.

Figure 1.8 Placing a conductive wire, in wich flows current, between poles of a permanent magnet, it receive a thrust by a force that act ortogonally to magnetic flux and current direction; direction of this force depends from polarity of magnetic field and current. This phenomena is used in electric motors, where it make possible to create movement, but also in current and voltage gauges.

Figura 1.9 Fleming’s rule (also called left-hand rule).

More exactly, with I indicating the intensity of the current calling and d the distance from the point considered, the induction holds: B = (k x I)/d The k parameter is a constant that is, limited to the vacuum, µo/2 ; assuming the conductor in a vacuum, the formula becomes: µo x I

B = ———— (I) 2 x d µo is the magnetic permeability of vacuum and is worth 2 x 10-7 Wb/Am; indicates the ability of a material or air (or vacuum, if it comes to space devoid of matter) to be crossed by the lines of force of a magnetic field. Magnetic field in a coil If the conductor is straight instead of being curved loop (spiral) the field produced by the current flowing through it is formed by concentric circles to it. The magnetism in the coils is important because it explains the operation of the coils used in DC/DC converters and transformers, which are more coils together. The magnetic induction that occurs at the center of the coil, assuming that it is in a vacuum, is expressed by the following relationship: µo x I B = ——— 2 x r where I is the intensity of the current flowing in the wire and r the radius of the loop. When you must generate an electromagnetic field of a certain intensity, instead of a single loop is preferred to employ the solenoids, which are coils comprising a certain number of turns of wire juxtaposed and wound in the same direction; for these reason, a solenoid magnetic induction develops the intensity of which is equal to the sum of inductions obtained from the individual coils, since it is supposed to be the set of more coils connected one after the other and then having in common the same current. The use of solenoids allows to obtain very intense magnetic fields, to obtain which a single coil should slide in it currents of extremely high value. If the coil has a length (meaning not that of the wire used but the distance from the first to the last coil) much greater than its diameter (at least ten times) the magnetic field that is formed inside is uniform and its direction coincides with the axis of the coils, while the direction depends on the current and can be determined by the so-called left-hand rule: “if you put the palm of the hand on the side of the coil so that the current circles from the wrist to the fingers The open thumb indicates the direction of the magnetic field”. Generally, that what is stated for the single loop: the field product has the direction of the axis and the direction determined by the rule of the corkscrew, namely that of a right screw which rotates in the direction of displacement of the current. Magnetic induction in the coils As regards the intensity achieved by magnetic induction, whereas a solenoid much longer than its diameter can be said that it is the sum of inductions due to the individual coils; more exactly, amounts to: µo x I x n B = ————— l where n is the number of turns and the length of the agreement between the first and the last coil. There are cases in which, for increasing the magnetic induction in the same space, it must achieve coils composed of multiple layers, in which case the solenoid is the set of more coils overlapping and the formula just exposed is no longer applicable. The value of the

magnetic induction is obtained probably using another report, which takes into account the diameter of the individual coils (d) and is as follows: µo x I x n B = ————— (l² + d²) This formula is also applicable to so-called short coils, those, that is, in which the length is not much greater than the diameter, but comparable to it. Electromagnetic induction When a conductor, not connected to any source of electricity, is immersed in a magnetic field, at its heads develops an electric voltage (EMF) impulsive, maximum top and descending, up to zero, with the passing of time. When the magnetic induction is due to an electromagnet powered variable current, electromagnetic induction occurs until there is variation and determines, to the heads of the conductor immersed in the field, a voltage that varies in analogy with the current in the electromagnet. Still, if the conductor is moved within the field, it manifests itself in an induced voltage, whose trends over time that it takes depends on the orientation with respect to the lines of force of the magnetic induction. This is the principle of operation of electric motors, whether they are in continuous or alternating, but also of the electricity generators such dynamos and alternators. The magnetic flux is the density of the magnetic induction in a certain field and for a given angle; strictly depends on the intensity of induction and the surface within which it is considered, according to the relation: = B x S x cos where B is the modulus of the magnetic induction vector, S is the surface within which considers the flow (expressed in Weber) a and the inclination of the conductor immersed in the magnetic field. More exactly, in the case of a straight wire is the angle formed by the perpendicular to its direction with the direction of the force lines of the field, while if one takes into consideration a coil, is the angle formed between the axis of this and the lines of force of the usual field. Since the flow depends on the angle with which the conductor is disposed in the magnetic field, rotating the conductor itself is obtained by a variable voltage that, if rotation is uniform and ranges from 0 to 360 °, assumes a sinusoidal shape. When considering the induction due to an electromagnet, the induced voltage should be noted as it has an amplitude such as to produce, if the circuit of the conductor or the loop is closed, a current that tends to oppose to the one that has generated. In other words, if in electromagnet the current increases in value, the magnetic flux that invests the conductor, but in it the current reacts developing a magnetic field that goes to oppose to the one created by the magnet. Returning to the voltage induced in the conductor, there is evidence that a direction such as to be the opposite of what should have considering the Fleming’s rule in practice produces, if the circuit is closed on a user, a current flowing in the direction of a left screw advancing in the direction of the magnetic field lines due to electromagnet. Mutual induction The phenomenon of electromagnetic induction occurs not only when a conductor is located in a stationary magnetic field of variable intensity or moving in a constant field, but also within a solenoid or a simple coil of wire, the tension has induced polarity and

amplitude such as to oppose the action that caused the current flow and the magnetic field, so that generated the fem induced. The phenomenon is called mutual induction or parts and explains why the coils with respect to an inertial character of the current: voltage applying them, initially they do not absorb anything, then, over time, begin to be crossed by electricity; suspending abruptly the supply voltage, tend to remain current, so that if you open the circuit but the breakpoints are very close, partly an electrical discharge (arc) that goes from one to another and can cause melting of contacts. Exploiting this phenomenon have been made important devices such as the ignition of the fluorescent tubes in neon, used in lighting, but also the DC/DC converters winding inductance, type of buck and boost. In a solenoid path by electricity, placed in a medium to magnetic permeability constant, the flow due to induction ( i) is expressed by the relation: i = L x i where i is the intensity of the current which originates, instant by instant, the flow, while the parameter L is called autoinduction coefficient or inductance. Corresponds to the trend that a solenoid has to develop the magnetic field and the induced voltage, which are opposed to the magnetic flux: the more is high, the greater, for the same flow, the reaction developed, and viceversa. In according to International System, inductance are measured with henry (1 henry = 1 ohm x secondo); inductance is like an electrical resistance, which shows itself when circuit in which is placed works in variable regime. In this conditions, resistance due to inductance grows in direct proportional ways related to frequency. Note that by the precedent formula on understand that magnetic flux variation, intended in a time-bit which duration in infinitely small (derivate) is amount of: d i = L x di where di is the current variation considered in an instant of the same duration of the infinitesimal within which examines the change in the flow. Due to this formula we obtain the value of the autoinducted voltage, which results to be: Autoinduction in electric coils Since an electric coil is build from more turns and each of these causes a proper induced magnetic field, is right to say that value of inductance depending directly from turns number of solenoid. Furthermore, it need to note that inductance depends on intensity of flux of magnetic induction vector; since this flux have a directly proportional relation with magnetic permeability of environment where coil is located, inductance is directly proportional to magnetic permeability too. Thus we can say that if a magnetic coil is wrapped in air (without magnetic core) it shows a behaviour different from a magnetic coil wrapped on a ferromagnetic core; more exactly, since metal is more available to respond to magnetic phenomena, it has more magnetic permeability, thus it causes more induction. To calculate in easy way a coil inductance we must to consider some typical shapes in which it comes: linear and toroid. For the toroid (ring of ferromagnetic material) turns of solenoid are wrapped all in the same direction, starting from a point and going along the circumference; since this kind of winding is made on a core that have plain magnetic permeability (we say this because toroid is made from same material in all of this zone and we can suppose it have plain density), we can start to calculate the flux caused by a single turn of solenoid. This magnetic flux is equal to: µ x I x S = µ x H x S = ———— l

in which S is cross-section of turn, born from ² equation (r is ray of turn) and l the length of solenoid if we imagine of develop it linearly, while H is magnetic field (keep in mind that magnetic flux is equal to magnetic field strenght multiplied by section in which we consider it). Note that µ is parameter we named absolute magnetic permeability of media in which magnetic flux acts and is equal to µo multiplied by µr; this latter takes the name of relative magnetic permeability and is typical of every material; relative magnetic permeability assumes very low values (a few units) in paramagnetic materials, while reach thousands of units in ferromagnetic materials (simple iron, ferrite, iron-silicon alloys). Relative magnetic permeability is equal to 1 in diamagnetic materials, in which absolute permeability (µ) corresponds to these of the vacuum (µo). So, the magnetic flux of entire solenoid is equal to addiction of fluxes caused by all the turns of windings, thus if we call N the number of the turns, comes equal to: = µ x H x S x N = — ————— From this equation we can obtain concatenated flux of solenoid, equal to: µ x I x S x N² c = x N = ——————— l So, total inductance of solenoid depends from concatenated flux c, according to following equation: c µ x S x N² L = —— = —————— I l These same formula, we can use to obtain value of inductance of a toroidal solenoid, can be applied to linear solenoids having enough precision, but only if lenght of solenoids is at least five times diameters of their turns.

CHAPTER 2 PASSIVE ELECTRONIC COMPONENTS To find the faults and repair the notebook, you have to know the main active and passive electronic components used in them. In this chapter we will focus on passive components, so called because they suffer the effects of the current. Their operation is explained by the electrical engineering and have an impact on current and voltage limiting the intensity and amplitude, or by varying the phase relationship that exists in the circuits operating in AC . Passive elements are resistor, capacitor and inductor; all have two terminals, namely two electrical contacts, apart devices variables such as the potentiometer, which count three contacts. Each passive component is identified by a value, which is that of its characteristic size; for resistors is the resistance, for the inductance coils and capacitors for the capacity. Moreover, for the heating elements defines the maximum power to be dissipated, for the inductance, the current and bearable for the capacitors the maximum applicable voltage, even if in reality also capacitors and coils dissipate power and therefore need to define the power bearable for them too. Finally, for the passive component is also specified tolerance, understood as the difference between the theoretical value written on the component and what could be a reality. For example, when it has a tolerance of 5 %, for example on a 1.000 ohm resistor having a resistance, it means that the exact resistive value can be between 950 and 1,050 ohms.

The resistor Also improperly called “resistance”, resistance to the passage of electric current, its value is expressed in ohms (is 1 ohm resistance that traveled by 1 A of current does

Figure 2.1 Carbon layer resistor, capable of ¼ watt power dissipation. Figure 2.2 Wire power resistor with heatsink.

fall between its extremes 1 volt voltage) or even in its multiples, which are kohm

(kiloohm) equivalent to 1,000 ohms and Mohm, equivalent to 1,000,000 ohms. The resistor behaves in the same manner both in current and in alternating and, in the case of voltage and current variable, regardless of the frequency, and this, at least in theory, because in practice is suffering from parasitic components (capacitance and inductance ) that you make feel , especially at high frequencies. The resistors are in trade in various shapes and dimensions, which depend on the use , in addition to the electric power which must be disposed of and from the maximum allowable voltage between their terminals. The normally used in electronics are presented as having cylinders at the sides, axially , the two terminals; sometimes have a tapered shape , while other times they are in the box. On the constructive, the resistors are different depending on the intended use, or the power, and their size depends mainly on the resistivity of the material used, ie, the specific resistance, typically measured in (ohms x m)/mm², because it is related to unit volume. The resistors can be constructed with a mixture of coal and other materials, dosed in order to obtain a specific resistivity suitable to obtain the desired strength. The kneading technique has been virtually abandoned because it results in a poor function at high frequencies , due to the large parasitic components (eg capacity due to agglomeration of the granules forming the dough) ; also the resistors slurry have a relatively high tolerance (from ± 5 to ± 10 %). Al type slurry is preferred for decades the resistor to the metal layer, the structure of which consists of a cylinder of insulating material on which is deposited a metal layer with a dosage and a thickness dependent resistivity that you want and the power to be dissipated. To adjust the value, the precision resistors is incised with the laser layer, so as to increase or reduce the resistance . A manufacturing technology that is similar to carbon layer, where the cylinder is deposited a layer of carbon whose concentration is much higher, the lower should be the resistance of the component to be built; also here we use the laser beam burn part of the layer and correct the resistance . The metal film resistors have a high tolerance, ranging from a maximum of 5 % to just 1%. The power dissipated by this kind of resistor ranging from 0.125 (1/8 ) of watts , for miniature models, 2 W for the power ones. The precision resistors are metal film, because, in addition to ensuring a very low tolerance on the resistance value, have a remarkable thermal stability for stability is the variation of the resistance value when the temperature changes. In fact, in the resistance value increases in direct proportion to the temperature value. The stability is expressed by a parameter called the temperature coefficient and expressed in ppm , or parts per million per ° C, to give you an idea of what it is, let’s say that in a resistor from 1,000 ppm increases the electrical resistance of one per thousand to each degree Celsius increase in temperature . For example, an element 1 kohm to 25 ° C at a temperature of 100 ° C has a resistance of 1,075 ohms. The resistors for SMD are made on a foil inserted in a parallelepiped with the terminals on two sides , and the adjustment of the value is done by cutting into the surface of the lamina. At this time, SMD components take, day by day, place of common components (THT) in a large variety of electronic circuits, including PC and notebook mainboard. The resistors that must dissipate more than 2 watts are made by wrapping several turns of wire with high resistivity on a cylindrical support , to obtain a certain resistance value , for the same length of the winding is played on the diameter of the conductor . Wirewound resistors are used to test the AC / DC notebook , as will be explained in Chapter 9. Coding of THT resistor The resistors designed to trough hole mount (THT) are on the market in standard values

grouped in series, the most common of which are the E12 (base 12 values), the E24 (base 24 values) and E96 (96 basic values). The base value refers to the components (those up to 2 watts) to mix and layer, where the value is represented by a color code, for the base value is defined as those first two digits (significant digits) of this code. The choice depends on how accurately the series should be the value of the component in the circuit, in the sense that if a large tolerance is allowed, one can use, for example, a 12 kohm resistor in place of one to 11 kohm. place of one to 11 kohm. 1.8-2.2-2.7-3.3-3.9-4.7-5,6-6.8-8.2, it is still most commonly used in the series , at least in the circuits that do not require a certain precision . The Intermediate Series (E24) already has more intermediate values , and is the most commonly Series (E24) already has more intermediate values , and is the most commonly 3.6-3.9-4.3-4.7-5.1-5.6-6.2-6.8-7,5-8.29.1 . Typically, the components of the E12 series have a tolerance of 5% , and those of E24 are all 1% or 2%, while those of E96 are 1%. The resistors normals are marked according to a color code that expresses the value, but also tolerance and temperature coefficient, the code is made with colored rings or bands that run around the body and are put in a certain order. Looking at the code, however, can raise a doubt as to which end to calculate the value? We must say that normally the E12 series resistors have tolerance gold (5% ) or silver (10%) so it is clear that the values are counted from the opposite side. In the components in which tolerance is brown (1%) or red (2%) typically stands out because it is the end distant from the others, otherwise the end of the first significant digits can be recognized because it is thicker than the other. Table 2.1 applies to resistors E12 and E24, while those of the E96 series are typically present three significant figures, or five bands of color. That , then, Table 2.2 . Normally the resistors with only four bands of color are those with a tolerance of 10%, 5% or 2%; those 1% have always five bands and are series E96 . There are also high-precision resistors, with tolerance even at 0.5% , 0.25 % and 0.1%; these have a sixth end (the side opposite to the one that indicates the first significant digit, that is the widest) which indicates the temperature coefficient.

COLOUR 1^ ring 2^ ring black - 0 brown 1 1 red 2 2 orange 3 3 yellow 4 4 green 5 5 blue 6 6 violet 7 7 grey 8 8 Table 2.1 Colour code for E12 resistors: tipically, this resistors have 5 or 10 % tolerance, but sometimes 1 %. First ring define

first cypher of base value, second is the second cypher and third correspond to multiplier. Fourth ring indicate tolerance on resistance value. 3^ ring 4^ ring x1 - x10 - x100 - x1.000 - x10.000 - x100.000 - x1.000.000 x107 - -

22 www.riparazione-notebook.net 5 % 10 %

Variable Resistors The resistors described so far are called “fixed” because they have constant values. However, there are resistors whose resistance can be varied , for example, to obtain the volume of audio or control voltage of a switching power supply , and these components are generically called Variable Resistors and potentiometers and trimmers. In fact the two are the same thing: they have three terminals, two of which correspond to the ends of the resistor and a third is the cursor, ie an electrode which runs along the resistance between it and allowing to have a value that varies from zero to that maximum measurable between the terminals. Of Variable Resistors manufacturers always define the latter value, which is why when we say that a trimmer or potentiometer is, for example, 10 ohms, means

COLOUR 1^ ring 2^ ring 3^ ring black - 0 0 brown 1 1 1 red 2 2 2 orange 3 3 3 yellow 4 4 4 green 5 5 5 blue 6 6 6 violet 7 7 7 grey 8 8 8 white 9 9 9 Table 2.2 Colour code used in E96 series resistor, that have three rings to define resistance value, one to indicate multiplier and a fifth to indicate tolerance. 4^ ring 5^ ring x1 - x10 1 % x100 2 % x1.000 - x10.000 - x100.000 x1.000.000 - x107 - - -

goldwww.riparazione-notebook.net5 % silver 10 % 23

Figure 2.3 - Some resistor trimmers for THT mounting.

Figure 2.4 A kind of THT potentiometer.

that the component has a resistance of 10 ohms between the extremes, namely that maximum resistance that can take is 10 kohm. Among trimmer potentiometer and change the appearance and constitution: the trimmer typically has a slot to adjust the position of the cursor with a blade screwdrivers, while the potentiometer has a pin to apply a knob; also the trimmer is designed to be touched up a few times, while the potentiometer is designed for continuous adjustment, so it is more hardy, both in the mechanics that in the resistive layer, which is made to resist wear that cause frequent movement of the cursor. The resistive element, which is the resistor itself, is accomplished by depositing a film made of dough (typically based on carbon) on a plastic support; cone is also the trimmers in cermet, a ceramic based compound. There are, however, power wire potentiometers: the resistive element is, therefore, a wire, wrapped almost approached on a toroidal support; the cursor is a plate that runs on it, moved by knob. The resistance is willing to bow and adjusted by turning and sliding the cursor in a circle. The common potentiometers are normally available in three versions: rotary multi-turn rotary and slider: the latter has a slider that slides linearly along the resistive element which is in line. There are also multi-turn potentiometers or trimmers, where the pin or the adjusting screw have a gear ratio capable of performing a complete excursion of the

resistive element in a number of revolutions which varies from 2 to 20 . And trimmer potentiometers can be used in two circuit configurations: a rheostat and variable divider; the first is basically a variable resistor, and then connect one end and the cursor (Figure 2.5). In some cases you see connected together one extreme terminal (one end) and the cursor, to constitute a single electrode, and the other end to the second electrode. As to the configuration variable divider, constitutes use by potentiometer real and serves to obtain a variable voltage: the extremes terminals are fed with a potential difference, and between the cursor and one of them is obtained by a voltage whose amplitude increases as hand you move away from the extreme which it refers (by contrast, decreases the voltage measured between the slider and the other end). The configuration of a variable resistor like a potentiometer is shown in Figure 2.6. In both configurations, the component (or trimmer potentiome

24 www.riparazione-notebook.net

Photoresistor

Figure 2.5 - Trimmer or potentiometer connected like a rehostat.

It is a resistor ( also said photoresistor ) in which the resistance varies according to the light that strikes the surface, is used as a photocell or also in the circuits of automatic variation of the brightness of the screen of the computer in function of the light in the environment. The photoresistor is composed of a resistive element resting on a support and covered with a protective layer that allows it to remain exposed to the external environment; layer is obtained with a mixture of semiconductor material, which typically is cadmium sulfide (CdS ) or cadmium telluride (CdTe). When hit by the light, the compound sees the shrink its resistance, which by some Mohm in the dark becomes up to a few hundred ohms in bright light. As all resistors, also the photoresistor has only two terminals and is made to travel from the current equally in both directions. The graphic symbol of the photoresistor is that illustrated in Figure 2.7. Thermistor The termistor is a particular resistor used to detect the temperature and until a few years ago was placed under the CPU socket (eg in AMD Athlon socket 462 and socket 370 Intel Pentium III) to detect overheating and heat alarms activate. The thermistor varies its resistance as a function of temperature. The thermistor exists on market in two types: PTC; acronym of Positive Temperature Coefficient, is a component in a positive temperature coefficient, in which the resistance measured between terminals increases with the temperature; NTC; that has a negative temperature coefficient (NTC derives from Negative

www.riparazione-notebook.net Trimmer or potentiometer connected like a potentiometer (variable resistive voltage divider). 25

Figure 2.7 - Graphic symbol for the photoresistor, used to draft electric diagrams.

Temperature Coefficient) and in it the resistance decreases as the temperature increases. The NTC thermistor is not very linear, this meaning that the relationship between the temperature and the resistance between the two terminals is not first-degree, in other words, if an NTC presents 1 kohm to 50 ° C, it is said that 100 ° C are 2 kohm . Instead, the PTC is much more linear, although it is only within a certain temperature range: under a temperature specified by the manufacturer (temperature switching) reverses its behaviour and works like a NTC. The thermistors have high sensitivity and fast response, but they are fragile and cover a limited temperature range, between approximately -100 ° C to +200÷300 ° C.

The Capacitor It is a reactive component, in the sense that it reacts to the stress producing in response action; while resistance dissipates energy, the capacitor stores it and then return it. This, at least in theory, because in practice, something is lost. The capacitor functions as a spring , which, after being pressed (loaded) extends and vibrates up to return to normal, it is formed by two plates of electrically conductive material, parallel to each other (or rolled up, one on the other, but always equidistant) said armatures; between them is the dielectric element, ie, an insulator, which may be air, paper, plastic, metal oxide or more (Figure 2.10). Each armature is connected to an electrode (or head) of the component. Applying a continuous voltage across the capacitor, the armature which is connected to the positive pole becomes electrically charged; removing voltage, the capacitor remains charged like a battery and has, between the plates, a voltage difference equal to the voltage of the battery that have charged it.. To discharge it, must be connected between the heads something that dissipates the stored energy: for example, a resistance. Initially feeding a capacitor discharge, or by applying a voltage to the armature

26 www.riparazione-notebook.net Graphic symbol for the thermistor, used to draft electric diagrams.

Figure 2.9 - Some kind of thermistor designed for THT (convenctional) mount.

of polarity opposite to that to which the component is currently charged, the capacitor absorbs current: this happens because the electric charge must move from plate to the other, passing through the dielectric. After the charge, there is no current absorption . The capacitor has inertial character in respect of the voltage, in the sense that, since when not charging , the potential difference at its terminals increases from zero to the value of the voltage source that is charging, in other words, while the current flowing immediately, the voltage increases gradually. The performance of voltage and current in a capacitor is always opposite in the sense that initially the current is maximum and the minimum voltage, then, to the rise of the voltage the current decreases to zero. The time taken by a capacitor to reach full charge, depends on the resistance that is in series, composed by the sum of the internal resistance of the voltage generator that is loading, the resistance of the conductors and the joints between them and any resistors places along the path of the current. The amount of storable electrical charge (Q) depends on two factors, which are the intensity of the current and the time for which it flows in the component, according to the equation: Q = I xt where I is the current of the charge and t the time charge. The amount of charge is expressed in Coulomb (C); 1C=1 ampere x 1 second. The capacitor is characterized by the attitude to store a certain amount of electric charge, which depends, in addition to the current consumption and the time, also on the voltage applied between the plates; this attitude is named the capacity (C) of capacitor, due to the formula:

Figure 2.10 Graphic symbol for capacitor: on the left image you can see symbol for not polarized capacitor (a sinistra) while on the right you can see electrolitic

C = Q / V The capacity is expressed in Farad or, more frequently, which are submultiples: the microfarad (µF) or 1 millionth of a farad, the nanofarad (nF) that is 1 billionth of a farad and picofarads, which is 1 millionth of a millionth of a farad (10-12 F) . The inertial nature of capacitor in respect of the voltage causes in that if a circuit is preceded by a resistor, in variable regime it reduces the amplitude of the voltage at its ends in a manner directly proportional to both the frequency, both to its capacity and the resistance but not only, because it brings in delay (up to 90°) the voltage over the current, causing a phase shift of the signal to their bosses. The capacitor that are in reality is a bit different from the model just described, in the sense that the parasitic components: an inductor (represented by the terminals) and a resistance, the latter is formed by two parts, one in series and the other in parallel. The first, called E.S.R. (Electric Series Resistance) and due to the terminals, slows the charge and feels especially on electrolytic capacitors, and the second is determined by the non-perfect insulation of the dielectric, which leads to a flow of current (almost negligible) even at full charge and determines a loss of energy. On the market, we can find the capacitor in various executions, with values from 1 pF to hundreds of thousands of microfarads; the dielectric can be paper, plastic (mylar, polyethylene, polyester) or a ceramic material, typically synthetic. So there are capacitors in paper, polyester or mylar, polypropylene, ceramic and ceramic multilayer. The electrolytic capacitor It is a type of capacitor that has high capacitance values with equal volume occupied. To obtain large capacity, in an electrolytic plate are thin aluminum sheets coiled spiral, one of which is coated with an oxide, which acts as the dielectric, the whole is dipped in a chemical solution (electrolyte) . The structure gives such a high capacity/size, but involves some drawbacks: first of all high especially resistive and inductive parasitic components, the latter are reflected in a high ESR and a loss of insulation in the dielectric is not indifferent. Secondly, the structure with electrolyte requires that the capacitor can not operate in alternating current and that should be required to be polarized with pos Ceramic capacitor: this is not-polarized kind and find application for filtering of power supply rails in mainboard and other boards of Personal

Figure 2.12 Electrolitic capacitor: it find application like ripple filter in linear and switching power supplies.

itive polarity on the + (plus) electrode with respect to the - electrode, otherwise the electrolyte will depolarize and the oxide which acts as dielectric is removed. In the first stages of the power of notebook computers and therefore, it makes extensive use of electrolytic capacitors with low ESR, since it has to do with very high switching frequencies. Alternatively adopt electrolytic tantalum, wherein the dielectric is an oxide of tantalum; these components have low series resistance and leakage current , and have a tolerance much more lower, but they cost a lot more than the common electrolyte. Furthermore, the tantalum capacitors are more delicate of electrolytic aluminum, so they may lose their isolation

COLOUR 1^ band 2^ band 3^ band black - 0 x1 brown 1 1 x10 red 2 2 x100 orange 3 3 x1.000 yellow 4 4 x10.000 green 5 5 x100.000 blue 6 6 x1.000.000 violet 7 7 x10.000.000 grey 8 8 - white 9 9 Table 2.3 Colour code for not polarized condenser in wich value are indicated using colored bands; to calculate value it always starts from upper band (the one far from electrodes). 4^ band 5^ band 20 % - 100 V - 250 V - - 400 V - - 630 V - - 10 % -

goldwww.riparazione-notebook.netsilver 29

more easily, for example due to an overvoltage between electrodes. Excessive temperature and time of use can accelerate the degradation, with the result that the capacitors, usually placed in the supply lines in order to filter the analog and digital voltages, they begin to conduct, at times periodically, causing two types of problem: reduce the power supply permanently, preventing the proper functioning of the integrated; leads casually, causing pulses which disturb the operation of the integrated and which are very difficult to identify. In the first case it is easy enough to figure out which capacitor will “leaks”, because just try it with the meter, while in the second it becomes quite difficult. The same is for capacitors whose dielectric “yields”, ie leads, only under voltage, when the tester can not be enough, given that the voltage that it applies to the tips in the tests ohmetric is of the order of a few volts. SMD capacitors used in notebooks are almost all in tantalum and differ from those in common dielectric because while the latter are stubby cylinder with two electrodes placed laterally at the bottom, tantalum are parallelepipeds with the contacts below (Figure 2.13). Coding of capacitors To indicate value of capacitors it uses a variety of systems, ranging from the color code in a numeric expression; are expressed with the color coding of meaning 1^ DIGIT 2^ DIGIT 3^ DIGIT LETTER first significant second significantmultiplier tolerancecypher cypher Table 2.4 Numeric coding for not polarized capacitors; multiplier is corresponding to the number of zeros to add to base value. NUMBER 1^ DIGIT 2^ DIGIT 3^ DIGIT (multiplier) 1 1 1 x1 2 2 2 X10 3 3 3 X100 4 4 4 X1.000 5 5 5 X10.000 6 6 6 7 7 7 -

www.riparazione-notebook.net Table 2.5 Number used in ciphers of numeric coding for capacitors; value is usually 30

LETTER TOLERANCE Table 2.6 Tolerance for capacitors in wich value is expressed by a numeric code. J 5 % K 10 % M 20 % Z -10 % ÷ +80 %

some components in paper, polyester and the like (in this case the code is similar to that used for resistors E12 series). Use the coded numbers ceramic capacitors, multilayer and common, some polyester or mylar and other types yet. Finally, the electrolytic have the value written in clear, normally expressed directly in microfarads ( for example , 10 µF 16 Vl). Table 2.3 illustrates the color coding used for capacitors in polyester and mylar , which provides for the marking of the body with five colored bands. To calculate the value, always starts from the upper band, ie the one furthest from the electrodes . In the color coding, the value is typically expressed in picofarads, so a capacitor that has the first yellow band, the second and the third green purple, worth 4,700,000 picofarads, or 4 , microfarad. Regarding the numerical code, using three digits and a letter: the first and the second defines the base value (are the significant cypher) and the third is the multiplier, ie the number of zeros, but add to get the value; the letter is the tolerance, which is worth 5% if it is J, 10 % if it is K , M, and 20% if it is -20/+80 % if it is Z. The letter of the typically found in some ceramic disc capacitors. The calculated capacity with numeric coding is always in picofarads. For example, 103 K identifies a capacitor from 10,000 pF ( 10 nanofarad ) with a tolerance of 10 %; M is a 104 pF capacitor from 100,000 (0.1 uF) to 20%. In polyester capacitors, especially those of greater value and higher cost, found the letter J, or the tolerance of 5%. But most of the ceramic has the letter Z or K , while with regard to the components in polyester, mylar , and the like there is the M or K. In ceramic capacitors in which the value is expressed with number code, sometimes you will find a colored band on the top , which indicates the temperature coefficient, and this because the ceramic have enough variations relevant capacity as a function of temperature (excluding NPO) then in some applications it may be necessary to notice also the drift. The ratio, expressed as usual in ppm, that is typically 100 if the band is red/purple, 0 if it

SMD electrolitics capacitors:

Figure 2.13

www.riparazione-notebook.net31 is black , if red -75, -150 If it is orange , yellow if -220 , -330 if green , -470 if

blue , purple and if -750 -1.500 if orange with a black stripe. The inductor It is a vital component for notebooks, as it is the base of the power supply operation, starting with the network at all stages that run CPU, RAM, video card etc. It is a coil consisting of a wire wrapped several times on a support diamagnetic (that does not interfere with the electromagnetic fields) ferromagnetic (which, in respect of the magnetic fields, it behaves like iron) or paramagnetic (which interferes, but little, with magnetic fields) that, crossed by electric current, sees manifest the phenomenon of mutual induction. The inductance value of the inductor is called and is expressed in Henry (1 H = 1 ohm per second) although inductors for electronics are typically marked in microhenry (µH) . The inductor has inertial character in respect of the current, because, fed in continuous, initially does not absorb anything, but is opposed to be crossed by the current; shortly after begins to conduct, and got used to a certain regime , try to keep it even if the circuit is interrupted. When powered, the inductor develops an induced voltage equal in value but opposite in the direction to that which generated it. The voltage, directly proportional to the value of the current and the inductance, is inversely proportional to the time in which it is viewed; means, ie, which is initially maximum, then decreases, until it reaches zero, as time that elapses from the time the coil receives power. In continuous regime, the inductor allows the sliding of the current regime (that depends on the sum of the internal resistance of the voltage generator and those of the conductors and the joints) only after a certain time interval, which depends on the total resistance in series and the same inductance value. The inertial behaviour in respect of the current causes the inductance feeding regime in the alternating current is delayed with respect to the voltage, in fact, at every change the inductor adapts slowly and it is left to cross from the current full speed only after a certain time. In a coil which has a resistance in series and working in alternating regime, the amplitude of the potential difference at its terminals decreases in a manner inversely proportional to both the frequency, both the values of inductance and resistance, the voltage moves in advance (up 90° ) with respect to the current. Normally, the value of the inductors is shown in microhenry (1 microhenry=10- 6 henry ) with the numeric code already described for the capacitors, but it is not

32 www.riparazione-notebook.net

Figure 2.15 Two SMD crystals used for example to get clock signal in the computer’s mainboards.

uncommon to find components which adopt a code of spot colors or bands; also in this case, it applies the color code of the capacitors and the value is always in microhenry. For example, if you find an inductor with three colored dots plus one, arranged in this order: red, purple, yellow, silver, means that the component is from 4.700 µH - 10% of tolerance. Note that often the colors are only three, because tolerance is taken for granted at 10%. Regarding the reading order, with the points you part from the larger, while with the bands you start from thicker.

Quartz Also and often named crystals, are electronic components used to stabilize the working frequency of the oscillators, by virtue of their characteristic to resonate mechanically at a frequency which coincides with that of electric resonance . Are used to generate the clock of the CPU’s and the graphics units (GPU’s) of the computer, as well as to stabilize the frequency of operation of the various stages. A quartz is formed by a metal box from which protrude two electrodes and on which is engraved the value of the fundamental frequency of oscillation. Inside the casing (Figure 2.15) is a disk of thin quartz, whose faces are coated with a thin layer of silver, are connected, through two small springs, which act as well as support elements, with the terminals. The thickness of the quartz determines the working frequency. Quartz is a piezoelectric material, and then subjected to a tension expands or contracts by following the trend, In contrast, if mechanically stressed produces tension. The crystals are used in the first mode: connecting them in an oscillator circuit, the voltage applied to them causes vibrations on the surface of the crystal. If the applied frequency is equal to the mechanical resonance , the deformations become macroscopic and a signal of small magnitude is sufficient to maintain the oscillations triggered. Then, the quartz has a high voltage to their bosses only in the presence of frequency equal to that of its resonance , while causes the oscillator does not produce anything or almost out of the resonance value.

In practice, each crystal is affected by parasitic components (Cp and R), which extend the range of frequencies within which it oscillates. The goodness of a crystal, understood as its ability to mantain the more precise and stable as possible the frequency of the oscillator in which it is inserted, depends on the factor of merit, that is Q=fo/Bw, where fo is the resonant fre Table 2.7 Dimensions of SMD passive code dimensions (mm) components related to series number.01005 0,4x0,2 0201 0,6x0,3 0402 1x0,5

quency, and Bw the difference between0603 1,6x0,8 the oscillation frequencies of maximum0805 2x1,25and minimum which actually character1206 3,2x1,6ize the quartz. In practice, the more wide the field of frequencies at which 1812 4,6x3 the quartz resonates with respect to the1913

4,8x3,3 resonance frequency fo, the smaller the 2010 5x2,5merit factor. Typically a quartz has a Q 2512 6,3x30of 80,000÷1,000,000.

In oscillators of microprocessors in 2615 6,6x3,2 general and in those used for the clock of the digital circuits, the quartz is connected to pi with two capacitors ( each of which has a head to ground) that initiate the oscillation . The range of values of the quartz is remarkable, however, is not always the desired frequency, in which case you can “fix” the frequency of a quartz oscillator by adding a capacitor (or even a compensator, that is, a variable capacitor) or an inductance. More precisely, it is added to lower the frequency inductance, while raising it fits a capacitor. Connecting in series with the quartz reactor and a capacity is realized a variable oscillator. What’s clock circuits of microprocessors and microcontrollers, the exact frequency value is obtained from quartz crystals of much higher frequency and dividing by counters. To achieve frequencies greater than that of quartz, the computers are used PLL-based frequency multipliers and counters, and the use of the PLL is the technique prince in computers, where quartz is the basis for a frequency multiplier that draws the clock CPU and chipset .

Figure 2.16 SMD resistor.

Ceramic resonators For several years are realized by components similar behaviour to that of quartz, but having as a piezoelectric element of a synthetic material, ceramic, in certain applications are preferred for the best resistance to mechanical stresses, temperature and humidity, but especially for the cost-sensitive application, due both to the fact that the sintered material in factory costs less quartz, both because it is easier to adjust the thickness with automated processes. The ceramic resonators are used as the quartz and are used in TV remotes in RF circuits and digital ones. Figure 2.17 - An optocoupler in SMD execution: it can be found in feedback network of galvanically insulated switching

power supplies, like the AC/DC of notebooks and desktop PC’s.

SMD passive components On computers and especially in the latest notebooks, resistors (including many power resistors) capacitors and inductors, but also the active components, they are almost always and almost everyone in the version for surface mount (SMD= Surface Mount Devices): no leads, or pins to be passed through the holes of the printed circuit board, but are mounted in direct contact of the slopes, thanks to contacts placed inferiorly or laterally in the lower part of the body, which can be of various kinds: a lamina, a plate etc. The SMD or SMT (acronym for Surface Mounting Technology), if you prefer, are used because they allow you to reduce the size of the circuits , as required by notebook manufacturers always want higher performance at the same weight and dimensions. Typically the contacts are positioned in correspondence of the short sides, but sometimes are found on the long sides, as in the case of some power resistors from a few ohms or ohm’s fraction. Compared to traditional components (THT, ie Trough Hole Technology ) those for surface mounting are distinct in series, each of which has specific dimensions. The format of the passive components such as SMD resistors and capacitors is defined by a number that indicates the size, designed by looking at the component mounted on the printed board , the width and length, expressed in inches, more exactly, the identification code is composed of two pairs of numbers, which are the decimal inch size or if you prefer, the size in inches without the comma in front. In other words, the pairs of numbers indicate the size of components in hundredths of an inch. For example, 0805 means that the dimensions of length and width are respectively 0.08x0.05 inches, or about 0.2x0.125 cm. Table 2.7 shows the correspondence between the code and the

Figure 2.18 On the right, green arrow indicates a not-polarized

Chapter 2

Figure 2.19 - Various kinds of SMD fuses used in Personal Computers and notebooks.

size of surface mount components. As for the values of the passive elements, the identification does not occur as the resistors common to mix or film, or on some polyester capacitors; here we use the numerical code already seen for ceramic capacitors and polyester without color code and what both also applies to resistors and inductors. For example, a resistor that has printed 102 K means that it is from 1.000 ohms, 10% of tolerance, a 473 J is from 47,000 ohms to 5 % tolerance. But often is the only value of resistance, capacitance, inductance, without tolerance, because that is defined by the specifications of the series to which the component belongs; therefore will more easily written the type 103, 473, 394 etc. It is clear that the resistance is the value indicated in ohms, while for the capacitors is in picofarads; for electrolytic, usually is printed the value in microfarads, so if we read 10 means 10 microfarad. However, it is not uncommon to see the electrolytic marking , especially those in small box (tantalum ) in picofarads, and 10 microfarads correspond to 107, ie 10 followed by seven zeros. Regarding the resistive networks, which are groups of resistors of equal value (collected in a single case) of which one terminal is shared or the terminals are all free, the value is stamped as for individual resistors; sometimes are indicated abbreviations which also identify the type (that is, the common terminal or independent). Special attention deserve the fuses in SMD, which is often present as thin plates with two electrodes on either side, but sometimes are rectangular in vertical section square (Figure 2.19). These components can sometimes be mistaken for resistors or capacitors, but usually show distinctive and still on the mainboard of the handsets are labeled by F (Fuse), the abbreviations are typically numbers that indicate the maximum current before the jump, then 1 , 4, etc. indicate currents of 1, 4 amps etc. Sometimes, in place of the fuses of the power resistors are used, however, metal film, and these are used as limiting the maximum current from a certain stage and are calculated to present , in normal conditions, a voltage drop that does not disturb the operation of the stages that follow and that are protected by the resistor. The SMD components should be treated and manipulated with care and must be removed using the hot air jet machine possibly combined with a heater that warms the printed circuit board, a good deal of flux will facilitate the dissolution of the solder allowing you to unsolder the component at relatively low and are not critical for his safety. You can also desolder and solder the SMD soldering iron with a fine tip, but it works only if the component does not have electrodes below, or if the majority of the surface of the electrodes is to the side.

CHAPTER 3 ACTIVE ELECTRONIC COMPONENTS In addition to the passive components, for the study of the notebook we are interested in those assets, which are the basis of operation of the main stages. The “active” are those components that today are based on semiconductor material or, better, of joints or special pairs of semiconductor material (in the past were vacuum tubes). They are so called because they do not just suffer the electric current but have an active role, in that they can decide how to behave in relation to its passage, or significantly change the parameters of electric power. They are active diode and transistor (bipolar junction, unijunction, JFET, MOSFET, IGBT) thyristors (SCR and TRIAC), so are the chips, which also include active elements. In this chapter we discuss the assets of “discrete” meaning discrete components that are found in a single case or, more precisely, will be explained diodes and transistors and bipolar field effect.

The diode It is the most simple active electronic component, today built by a semiconductor junction capable of being cross from the current only in one direction, at least in theory, because in practice also leads in the opposite direction, leaving, however, pass a current negligible. The diode is a component to two terminals that polarized with the anode positive with respect to cathode does not conduct until the voltage applied to it not exceed the threshold value; overcome this, the diode begins to conduct, first gradually and then abruptly, leaving cross from strong currents with minimum voltage variations to their terminals. The value of the threshold voltage depends strictly on the type of diode; existing types of what are PN junction diode, PIN, the junction diode metal/semiconductor and that a contact tip. The first is the basis of components widely used in consumer electronics and industrial , and the second is used almost exclusively in the switching converter and the third as amplitude modulation detector in radio receivers. The common diode (also said rectifier) is used where essentially serve to allow the passage of current in one direction, then in the power supply of the computer, such as current rectifier (where it serves to ensure that the alternating current taken from the network or from the secondary of a transformer loads of capacitors to obtain a DC component) or to dampen reverse voltages generated by the coils of the switching of the notebook. The junction diode is made by joining two semiconductor materials or metal: in the first case is of the type PN or PIN, while the second is a Schottky; the PN junction is actually a block of silicon or germanium (tetravalent materials that chemical ranking as semiconductors) the end of which are introduced impurities, ie atoms of trivalent or pentavalent elements; input operation is called doping and serves to create excess electric charge carriers (electrons) from one side and shortage of them other. The area doped with atoms to five valence is called N region and constitutes the cathode, while the one with trivalent doping is the region P, or cathode. To conduct the PN junction diode must apply to it a potential difference of opposite value to that (potential barrier) created at the extremes of the depletion region. The voltage must be positive on the anode (area P) with respect to the cathode ( area N) so as to push the

excess electrons in the N region to move in P, its value must exceed that threshold, corresponding to the electrical potential necessary to take away the electrons went to fill the gaps in the proximity of the depletion region from the same shortcomings. The voltage required to run (threshold voltage) is 0.6 V for the junctions composed of silicon and 0.2 V for germanium ones, there are also synthetic semiconductors, used mainly in the production of light emitting diodes (LED) in which the voltage threshold may be higher (up to 4 volts). Inversely biasing the diode, ie with the anode (area P) negative with respect to

Figure 3.1 - Characteristics 40 www.riparazione-notebook.net dia gram of a PN junction diode and graphic simbols (used in schematic diagram) of this component.

Figure 3.2 Sample building of a PN junction wich is the base of silicon and germanium PN diodes.

the cathode (N) the component does not conduct, if not the weak reverse saturation current until, exceeded the breakdown voltage, the junction does not yield and leads to the snowball effect . The threshold voltage, as the maximum reverse bearable by a diode, and all other parameters characteristic of the diodes, are supplied by manufacturers. Of the PN junctions of diodes and transistors, the current in reverse bias (Io) doubles every 10 °C of temperature increase, while the threshold voltage Vs is lowered to 2.5 mV per °C of temperature increase. PIN diode The PIN diode is a special variant of the PN: always consists of a junction, but the region between the N and P shows an area of intrinsic (undoped) semiconductor insulator, which widens the depletion region. The enlargement allows to obtain high reverse breakdown voltages, and then to use the PIN diodes as rectifiers in high voltage circuits. The PIN structure also allows recovery time (transition from conduction interdiction) smaller than those of the traditional region PN, which makes it suitable for the diode to operate as a rectifier in switch mode power supplies and in any case in the event of switching circuits where high frequency and where a common diode would also lead to the first moments of the reverse bias. The threshold voltage of the PIN diode is higher than that of the common PN junction diode. Schottky diode It is a special diode where the junction is formed by the fusion of a metal on an N-doped semiconductor, where the metal is the part P, more exactly, the metal is aluminum and having valence +3 acts as a dopant trivalent. In the area concerned to the contact metal/semiconductor is formed the usual depletion zone , devoid of free charges and then insulating , at least until the semiconductor between N and the aluminum electrode is not applied a voltage higher than the potential barrier. As for the PN junction diodes and PIN, even for the Schottky direct polarization consists in applying the positive polarity to the region P and the negative to N,;the threshold voltage, however, is very low: just 0.3 volts . This makes it ideal Schottky diode for low voltage circuits . Another important characteristic of the Schottky diode is the high switching frequency from conductive state

to interdiction state, which makes it very suitable for the realization of switching power supplies and electronics for the drive pulse; the diode rectifier is usually used as much of DC/DC converter laptops, but also of external power supplies AC/DC.

Figure 3.3 - Aspect of a generic diode: the colored ring indicates cathode electrode (K) that is terminal it must to bias directly if diode are used like a rectifier and inversely if diode is a photodiode or Zener

Zener diode It is a diode that allows to stabilize the voltage. To understand the operation must resume that of PN junction diodes, of which it is seen that in reverse bias carry no current, if not that negligeble value called “leakage current” or “reverse saturation current”. Beyond a certain voltage value, however, the junction breaks down and the current increases dramatically, becoming almost independent from voltage. It is in this area of the feature (3rd quadrant ) working those particular called Zener diodes , which are designed to run indefinitely, with certain values of current, without damage; in other words, a Zener diode, when it reaches its threshold voltage reverse (named Zener voltage) takes to conduct and the current is practically limited by a resistance that wants in series (ballast resistor). The voltage across it remains practically constant for any value of current, at least in theory. This feature makes it ideal for making circuits Zener voltage stabilizers, power supplies and in any case where a servant constant reference voltage. In direct polarization, it behaves like any Zener diode. In the following chapters you will see how it takes to stabilize the voltage in the power supply, but for now, be content to know the typical bias circuit, reverse course. The adjustment of the tension arises from the fact that, within certain margins, any variation of the current in the diode resulting from a change in the value of the supply voltage of the Zener bipole/ballast resistor or by a variation of load absorption, leaves practically unchanged the Vz. In fact, the voltage drop of the Zener diode, after the rated voltage, remained almost constant.

www.riparazione-notebook.net Figure 3.4 - Biasing circuit of the Zener diode. 42

The light emitting diode (LED) Each PN junction diode, when it is polarized directly, emits radiation; in the germanium diodes and silicon diodes the emission occurs in the infrared region (over 750 nanometers). But there are diodes in which the light is emitted in the visible range: they are called LED (Light Emitting Diode) and are made with synthetic semiconductors, capable of emissions in the range of wavelength from 450 to 700 nm. Like all diodes, even the LED conduct current (and light) only when the direct voltage applied to their bosses exceeds the threshold, this is not equal for all the LED but depends on the color, or better, grows going from red to blue, because red is the lowest extraction potential (about 1.8 V) while the blue LED , which give the light radiation to higher energy (shorter-wavelength) to extract the electrons serves a potential that can reach 4 volts. The semiconductors are artificial compounds from different elements to achieve various energy levels, and then various wavelengths and colors. The materials used for the LED are typically: gallium arsenide (GaAs ); allows to obtain mainly red light emitting diodes, with wavelengths ranging from 640 to 700 nanometers; gallium arsenide and aluminum (GaAl-As); manufactures light emitting diode lightemitting red darker than that of gallium arsenide (650÷720 nm); arsenide and gallium phosphide ( Ga-AsP), with it you realize that the LED color of the light depends on the percentage of phosphorus with the phosphide and gallium arsenide diodes are built in red light from 640 nm down, but also orange (around 600 nm) and yellow (550 nm); gallium phosphide (GaP); with this semiconductor are built light-emitting diodes that emit green light (up to 500 nm) but also blue and yellow; gallium phosphide doped with zinc and oxygen, allows to realize LED issuers on the border between red and infrared; indium arsenide, gallium and aluminum (InGaAlAs) allows to obtain emitting diodes in various parts of the spectrum, namely red, orange , green, but also in the infrared; checking the percentages of the components of the semiconductor, they can range between 550 and 800 nm; phosphide, gallium , aluminum and indium, with it you realize joints capable of emitting mainly red and yellow light (550 to 700); indium and gallium nitrate (InGaN) LEDs produces light emitting dark green,

www.riparazione-notebook.net Graphic symbol used in schematic diagram to indicate the LED. 43

Figure 3.6 Internal view and connections of a LED in classic dome case.

blue and, especially, white, with color temperature of the order even higher than 4,500 ° K. The LEDs are born to replace the lamp filament bulbs and neon in the panels of machinery and electrical and electronic equipment; in notebooks are used as indicators of ignition, battery or mains is present ( power supply unit AC/DC) activity hard disks or CD/DVD players etc., but also as backlighting of LCD display , keyboard, and the area in front of the webcam built into notebook possible. The photodiode Exposing the PN junction in a light, but also infrared or ultraviolet, in the semiconductor frees a number of electrons proportional to the intensity of illumination. If the diode is reverse biased, its reverse saturation current Io increases accordingly. The diode, in this case operates in the photoconductive dial. The PN junction diode constructed so as to leave exposed to light is called the junction photodiode; in it the seam is made so as to look out outside the side doped P, which, for the purpose, is made the most extensive and thin as possible (the N is instead made very thin, to let the light pass trough it. The photodiode is used as a light sensor but also to receive signals transmitted in the form of light from the infrared LED, and then in the remotes, in wireless headsets and receivers for optical data link, is also the base of the optocouplers. In the notebook is used both in the infrared ports (IRDA) is in the readers of CR- ROM and DVD as a receiver of the light reflected from the surface of the CD. Laser diode It is a semiconductor-based component used in CD-ROM and DVD, but also in recorders, to generate infrared light required to read or write data; the laser is preferred to the traditional LED (although this is also a generator of light) because it produces a very focused and collimated beam of light at short distance, but also because the light produced is coherent, that is concentrated in an extremely narrow spectrum which theoretically coincides with a single wave

44 www.riparazione-notebook.net Figure 3.8 A BPW34B photodiode: it is one of the most used photodetectors and is capable to detect light both visible and infrared. It is epmployed in IR remote controls and in a whole applications where it need to detect infrared.

length (the light emitted by the LED is instead the set of multiple wavelengths). The laser diode is based on a junction, typically gallium arsenide and aluminum, which produces a light radiation reflected from a reflective surface and that is able to exit, after being reflected several times, from a second surface, semireflective, the latter let the photons light components only when their wavelength is consistent with a certain value. The many reflections cause the light is very concentrated. The laser diodes used in CD and DVD burners and have very limited powers of the order of maximum 1 or 2 mW; must, however, be very careful not to look at when they are on, because the light they produce can damage your eyes. So if you open a player from a CD or DVD you have to do when it is off.

The bipolar transistor Also called simply transistor , has been the cornerstone of logic, memory and microprocessors TTL. It is actually only one of the existing types of transistors, but it is the oldest. It is an active component, meaning by this transistor is able to act on a current controlled by another, and is formed by two PN junctions juxtaposed according to two schemes: NPN; finger of semiconductor is doped to the extreme N and P type in the center; PNP; finger of semiconductor is doped to the extreme P and N type in the center. Since that consists of PN junctions oriented in either towards, is also said BJT, acronym of Bipolar Junction Transistor (ie bipolar junction transistor ); bipolar

www.riparazione-notebook.net Cutaway of a laser diode; this component is normally used to read and write optical disc in CD-ROM and DVD. 45

means that it works affecting the two types of electric charge that “move” in the PN junction, ie electrons (negatively charged) and holes (which are not charged but lack of electric charge and then determine, despite them, the exposure of positive charge in the area doped P). The outside areas of the transistor are called the collector and emitter. To make it work properly , you have to do in order to bias the base-collector junction and the inverse baseemitter directly . To understand how the transistor, we refer to the test circuit shown in Figure 3.11, which shows an NPN transistor, and imagine to forward-bias the baseemitter junction and inversely the collector-base. Exceeded the threshold voltage (Vbe, equal to the threshold voltage of the PN junction, and then 0.6 V for silicon transistors, and 0.2 V for those in germanium) from the area of the emitter electrons (electric charge carriers) is moving toward the base. Meanwhile, the base-collector junction is forbidden and it does not flow more than the weak inverse current already described for the diodes; elevating beyond a certain threshold the collector-emitter bias voltage, the electric field becomes such as to extend the zone of emptying and at some point it strips away the electrons occupying the base and who have not been placed in the holes of the P structure. The transistor is therefore within the two currents: one is basic and the other is determined by the flow of electrons which, coming from the emitter, in large part are sucked from the collector after a short transit in the base, the first is a current that is intense because of the junction directly polarized. The second, although due to the reverse bias of the basecollector junction is particularly intense: there is thus a phenomenon that is defined in electronic transfer of resistance, as occurs in the transistor of the transfer bias current of the direct circuit at low resistance of the emitter-base junction in the base-collector junction, which, being inversely polarized, is characterized by a high resistance. The name transistor was born out of this phenomenon and the composition of the words transfer and resistor. The characteristic of a current to flow particularly intense in a region of high resistance, or to slide in the base-collector junction virtually the same current flowing in the base-emitter, causes the transistor amplifies: in fact, if it maintains the same current a circuit with low resistance in a high resistance, the voltage drop Vbe determine a voltage between the collector and base (Vcb) proportionally higher. Regardless to the bias voltages , ie for both the NPN and the PNP, in a transistor emitter current (Ie) applies:

www.riparazione-notebook.net Graphic symbols used to indicate tran 46

Ie = Ic + IB Figura 3.11 Bias circuit of NPN transistor mounted in common emitter layout; these configuration is the same used when transistor have to work like a solid state switch, like in DC/DC converters of notebooks and in power switching.

The base current is very small compared to the other two and is more so the greater the gain of the component , ie its tendency to raise the current in the base-collector junction at the same current in the base. The relationship between collector current and base current is called the gain of the transistor and is: hfe = Ic/IB There is talk of gain or amplification coefficient because it is assumed that Ic is determined and modulated by the current that bias the base. This shows how both the base current to modulate the one that flows between collector and emitter, and how, therefore, the BJT is a current-controlled electronic device. The examples given so far taken into consideration NPN transistor, for which the base and collector currents entering the component, to get out, as the sum, the emitter (Ie ), but there is also the PNP type, for which the direction of the currents are down, as well as bias voltages. The rules are, however, the same. The bipolar transistor is used as a current amplifier and can work in a linear mode (the output component linearly follows the trend of the input voltage) or switched mode; works when it is linearly polarized so that the collector current and collector-emitter voltage are to a value that is half of the excursion of the linear zone (is defined as that part of the output characteristics in which the relationship between collector current and base remains almost uniform). The

www.riparazione-notebook.net Bias of NPN transis 47

Figura 3.13 real bias of a PNP transistor.

BJT works, however, in switched mode when working interdict or saturated, ie as static switch, in which case it is polarized because it gives the minimum voltage drop between the collector and emitter, without regard to the linearity. What distinguishes the linear operation from that as a switch is the fact that in the first case the transistor is polarized even at rest (when it should not treat any signal) while the second requires polarization only when BJT must to conduct current. Parameters of the BJT In addition to earning numerous manufacturers specify the technical characteristics necessary for correct sizing of the stages that are based on transistors. The most important parameters related to the common emitter configuration, are: V BE = voltage drop in forward bias between the base and emitter; VEB = bearable by the base-emitter junction voltage when reverse biased; VCEO = maximum voltage (reverse) applicable between collector and base to avoid damage, it is defined for IB=0, ie, when the base-emitter junction is interdict; V( BR)CEO = reverse voltage that causes the breakdown of the base-collector junction and the corresponding short circuit; if reached, the transistor becomes unusable; V CEsat = maximum voltage drop in saturation conditions; Maximum collector current IC = bearable continuously; base current IB = maximum tolerable continuously; ICEO = current flowing through the base-collector junction (in reverse bias) when the base-emitter junction is not polarized (I B=0); IEBO = current in the base-emitter junction in reverse bias; hFE = current gain (Ic/Ib) in continuous; the constructor specifies in correspondence of which the value of the collector-emitter voltage was measured; h FE = current gain dynamic, ie when the transistor is biased in the base with a variable current, typically at a frequency of 1 kHz; PTOT = maximum power dissipated by the component at the temperature of work defined by the manufacturer (usually referred to a case temperature of 25° C);

TJMAX = maximum working temperature of the joints; ja = thermal resistance between the semiconductor and the environment jc = thermal resistance between semiconductor container; when the transistor is encapsulated in a container that has a metal part, is the measured resistance between the semiconductor and the metal surface. knowing the parameters of the transistors is important when it must make a repair and maybe not in the house has a component of the same abbreviation, in which case one can consider the adoption of another transistor chosen from among those with similar characteristics. Configurations of the BJT The BJT can operate in three different layouts, each defined whichever is the terminal pooled (Figure 3.14): common emitter, common collector and common base. The first is the one used most frequently and is characterized by the fact that the transistor amplifies in power, ie both the current, as the voltage; presents high input resistance (base-emitter) and low output resistance (collector-emitter). The second amplifies only in current and is also called emitter-follower (emitter follower ) because the output voltage follows, perfectly in phase, than the input is the one normally used in the output stages of the voltage regulators and linear amplifiers power and has very high input resistance and output resistance is very low. The last (common base) is used in particular in the early stages audio amplifiers and antenna of radio receivers; has low resistance input and output voltage and amplifies only. Polarization of the BJT The transistor may be biased to operate as a linear amplifier as much as possible or by circuit in the first case is used for amplifying analog signals such as audio intended to speakers or the microphone incorporated in the computer, while the second serves to activate motors (for example those of floppy drives and CD) or electromagnets (to open the tray of the CD player) or to pulse on the internal chokes in switching power supplies or the network adapter. In operation as an amplifier, the transistor must have applied between base and collector (or between the base and emitter) a voltage greater than that present between the base and emitter: typically more than 4 to 5 volts. Feeding the baseemitter junction, it flows in a direct current whose trend is that already seen for the semiconductor diode, the current in the collector instead has a clearly different pattern, not linear: starting from zero volts and increasing VCE, initially there is a substantial increase of the current for slight variations of the collector-emitter voltage. At some point the growth of the IC is drastically reduced and it is said that the transistor saturates; further increasing VCE, beyond the point VCEsat, the current continues to grow but little and becomes less sensitive to voltage variations. When the transistor is used as an amplifier is necessary to exploit it in the linear region, ie in the section of the output characteristics in which there are slight variations of the IC for large variations in the VCE, and this is even more true as more needs to be accurate and distortion-free amplifier. The BJT can also be used as a static switch, to actuate users or to switch the power supply on the transformers (for example in switching power supplies and inverters): in this case works in saturation, ie with VCE less than or equal to that of saturation. Note that for saturation is defined as the operation of the transistor in a condition in which the VCE VBE can become comparable to or smaller than it, in such case, namely in the area of the

characteristics to the left of the point of saturation, the current gain of the transistor collapses. Well, so far we have seen how a transistor bias, neglecting the thermal drift and maximum power dissipated by the BJT. Regarding the thermal drift, it must be said that the transistor does not maintain a constant working point chosen in the design stage, but its polarization varies according to the temperature of the environment in which it is located; this because the VBE is lowered to 2,5 mV per °C increase in temperature and the reverse current ICBO collector doubles every 10 °C rise in temperature. As to the power dissipation, we must say that the working point is chosen respecting a simple condition: the transistor must not, in any case, disposing an electric power that is out of the SOA ( Safe Operating Area ) area that is defined by the manufacturer by means of a curve drawn on the output characteristics. In short, the power dissipation of the BJT, and may be considered to be essentially that of the collector-emitter circuit, can be calculated as:

Figure 3.14 - Circuit layout of bipolar transistor: on the left common emitter (A) , at the center common collector (B) and at the right common base (C).

Pd = VCE X IC neglecting the power dissipation of the base-emitter circuit. Each transistor can be disposed of only by a power that the manufacturer spec

50 www.riparazione-notebook.netFigure 3.15 - Various kind of SMD type transistors.

ifies a certain room temperature and note that you can easily calculate the total thermal resistance of the component; beyond that power, should be helped with devices that dissipate the heat produced, otherwise the joints are damaged. The power dissipation is a fundamental parameter to consider carefully before replacing a transistor with another during a repair.

The field effect transistor That of the field effect transistor, generically said FET (English acronym of Field Effect Transistor) is a broad family of components is very important in the computer world, because it has very quickly supplanted the common bipolar transistors in the control of motors and electromagnets , but also and especially in the power supply. Of this family are part of the JFETs and MOSFETs. JFET Also said Junction FET , the jFET (acronym for Junction Field Effect Transistor) is, as the BJT, a semiconductor amplifier component, but it works with only one type of electric charges and is driven in voltage rather than current. Also has an output circuit, the resistance of which is modulated by the potential difference applied to the circuit input or command, if you prefer. As the BJT, the FET is widely used in oscillators and in the transmitters (but also in common amplifiers and BF and RF); has the usual three terminals, called, however, gate, drain and source. The gate is the control electrode and can be coupled through a PN junction, and in this case the transistor is called jFET (Junction Field Effect Transistor), but can also be separated by an insulator, in which case one speaks of structure MOS (Metal Oxide Semiconductor) or MOSFET. The typical structure of the jFET (Figure 3.16) is a bar of doped silicon N (call channel) to the sides with a junction, that revolves around it, made spreading impurities P; the gate is headed to the junction and in this case one speaks of FET N-channel. Alternatively, the finger is doped P and the gate is in the area doped N: is the case of the Pchannel FET. The birth of the junction creates the usual depletion region, devoid of fillers, which penetrates into the channel. To find out how the jFET, suppose to biasing one Nchannel as shown on the right in Figure 3.16; the Vgs must be negative in the components on the gate of N-channel and P-channel positive in those. In resting conditions, ie with nothing Vgs, the channel between drain and source presents its typical resistance; polarizing the drain positively with respect to the source, the channel current is always flowing. Making gate negative, the depletion region widens and narrows the channel; in practice this causes an increase in the channel resistance and a decrease in the intensity of the drain-source current. Beyond a certain level of Vgs, the regions of emptying of the two sides are touching and the channel is interrupted and with it the current in the drain, and the value that causes what is called the pinch

Figure 3.16 Structure and test circuit of a Nchannel jFET.

off voltage. Instead, making the voltage Vgs positive, but always less than the threshold of the junction (0.6V) the channel widens slightly from the nominal condition and its resistance becomes a little lower than that at rest. However, the Vgs must always be negative or zero, otherwise the jFET absorbs on the gate, a condition not suited to his operation. The jFET is essentially a variable resistor (between drain and source) modulated by adjusting the voltage applied between gate and source. The source and drain terminals are theoretically interchangeable, because places at an equal distance from the gate. As for the BJT, JFET also can be used in three circuital configurations, which are common source, common gate and common drain. The exemplificative schematic in Figure 3.16 depicts the first configuration; the negative bias of the gate is obtained through the voltage drop on Rs, exploiting the fact that the gate does not absorb current and, therefore, despite the resistor Rg, it is as if it were connected to the source. In order to elevate as much as possible the input impedance of the amplifier, Rg can be chosen high value (for instance, 1 Mohm). The MOSFET It is an insulated-gate FET and consists of a bar of semiconductor in which two zones are made in opposite doping (P if the finger is N or N if the finger is P) between which is located an electrode isolated from it by means of oxidation. The MOS exists in two variants: in the Depletion Mode, that works like the jFET, normally finger ago by channel and presents some resistance between the

www.riparazione-notebook.net Figure 3.17 - Structure, graphic symbol and bias circuit for a N-channel MOSFET enhancement mode. 52

extremes, resistance modulated by intervening with an electric field on the gate (Vgs negative impact on the gate); what empties in whole or in part of free charges and the resistance increases. The current flow stops when it reaches the pinch-off voltage, or when the negative Vgs reaches a value such that the field of gate away all the electrons from the channel. Then there is the type Enhancement Mode (Figure 3.17) in which no current flows at rest between the extremes, because the channel does not exist; it is created by applying an appropriate electric field (positive Vgs on the gate) that attracts electrons under the gate, starting the run. In the latter type the driving starts just past exceeded the potential difference which is the threshold (Vgs threshold). In both, drain and source can be exchanged between them, because, although the channel does not have polarity, the source is internally connected to the substrate of the finger, so as to create the electric field of the command. To make a repair involving replacement of one of the MOS transistor of the power supply is necessary to know the main features of the failed component to replace, in particular it is necessary that the power of the MOSFET which will replace the faulty one is greater than that of the latter. The same applies to the voltage Vds. The resistance in the ON state (Rdson) must be less than or equal instead. MOSFET manufacturers usually specify: Vgsth = gate-source voltage that initiates the conduction between drain and source (that is only for the MOS filling) ; Vgsoff = pinch-off voltage , is defined for the MOS Depletion Mode and corresponds to the gate-source voltage which causes the interruption of drain current ; Vgsmax = maximum applicable voltage between gate and source ; Vdsmax = maximum applicable voltage between drain and source when the Id is nothing; Idmax = maximum continuous drain current; Rdson = resistance between drain and source them fully (to Vgsmax); Idss = leakage current between drain and source with Vgs=0; Igss = leakage current between gate and source or substrate with Vgs=Vgsmax; Ton = time taken from when voltage is applied between gate and source, to reach the corresponding Id; Gfs = transconductance (relationship between drain current and Vgs required to obtain it); Ciss = gate-source parasitic capacitance (defined because the gate circuit behaves like a capacitor); Ptot = maximum power dissipated by the component at the operating temperature defined by the manufacturer (usually referred to a case temperature of

25° C); www.riparazione-notebook.net53 Timax = maximum working temperature of the semiconductor ; jA and jC; have the same meaning as for the bipolar transistor. When replacing a MOSFET with an equivalent, if the repair relates to a switching power supply check that he has the same power and the same Vgs and Vds, but also that Ton is less than or equal; in fact Ton determines the frequency at which the MOSFET can switch if it is too long, the component has rising edges angled down, which in practice result in an increase of the power dissipation also decided (if the MOSFET pass instantly from conducting interdiction and vice versa theoretically consume only the minimum power given by the product of the Rdson for the drain current) and therefore the overheating of the transistor and the loss of efficiency of the switching in which it is mounted. As many transistors or Darlington, power MOSFETs are also internally provided with a protection diode, connected so as to conduct when the drain and source are polarized on the contrary: in practice, the diode has the cathode and the anode on the drain on the source in the Nchannel MOSFET and the source on the cathode and the anode on the drain in those Pchannel. In MOSFET products lately the protection diode between drain and source is replaced by a Zener, which in addition to protecting against reverse polarity, for its characteristic of conducting even in reverse bias than its Zener voltage, allows to limit the maximum Vds direct at rest (for example, when the transistor is blocked) of the MOSFET. For the ease with which one pilot, the absorption of almost zero gate and the very low resistance in the conducting state, but also by virtue of the switching speed of the power (always greater than that of the power BJT) the MOSFET is from favorite time of the transistor in the switching and the use of static switch, then in switching power supplies and switches that control the main power in notebooks. It is no coincidence, in fact, that in the switching present in the motherboard notebook transistors that switch the current to the coils are always and only MOSFET, N-channel or P, the same goes for the transistors used as static switches (task that the MOSFET performs better than the BJT due to the very low on-resistance on the channel that drainsource) placed along the main

Figure 3.18 - P-Channel 1.8V

www.riparazione-notebook.net specified MOSFET Fairchild FDS4465 in PowerTrench process. It has been optimized for power management applications with a wide range of gate drive voltage (1.8V÷8V). 54

power of the mainboard, used to turn on the power supply/battery charger or other switching blocks.

CHAPTER 4 INTEGRATED CIRCUITS In addiction to discrete components, Personal Computer are made using integrated circuits; rather, we will say that without them PC, and especially notebooks, would be great hundredfold. Integrated Circuit, is an electronic circuit made more smaller than equal made using convenctional discrete components (discretes) mounted on a classic PCB. To all the effects of an integrated circuit (or integrated, as we name commonly, or IC, an acronym for Integrated Circuit) is nothing else of a complete electronic circuit made in a single chip or electronic component package, to which it need to add some discrete components that owner had choice to place externally to avoid a variety of mistakes, from heatsinking to electromagnetic and/or electrostatic interferences. Integrated circuits can be found in two kinds: monolithics, if they are made on a single semiconductor chip; hybrids, when they are made employng either discretes or monolithics on a sublayer or support insulated such aluminium dioxide. The real revolution in IC was represented by monolithic, because on a single chip are not only diodes and transistors, but also passive elements such as resistors and capacitors. A monolithic integrated comes to be as small as a transistor, so that it is not uncommon to find components in a TO-92 case, such as voltage regulators of the 78Lxx series or thermal probes such as the DS18S20, which contains a digitizer and a one-wire communication interface, or the ZN414, which is a complete radio receiver. The advent of SMD components has resulted in the case which is much smaller and therefore takes up very little space. The monolithic occur in various shapes, the most common of which is rectangular, with the pins in two rows located on the long sides; this type of configuration takes the name of DIP (Dual Inline Pin). This is a standard which is characterized by a case provide of pinto-pin distance (pitch) and distance between the two rows of pins standardized; the pitch is 2.54 mm, while the lateral distance is 7.5 mm for the DIP smaller and 15 mm for the largest. Usually, DIP starts with cases having 3 pins on each side (used by optocouplers) up to even those 40 pins on the side; the IC’s from 3+3 to 10+10 are usually case-pitch 2.54x7.5 mm and beyond, in the case of 2.54 x 15 mm. But it is not uncommon to find exceptions, such as Microchip, which often use the side step of 7.5 mm, while it had 14 pins per side (e.g. PIC16F876 microcontroller). In addition to those described, there are cases of other shapes such as square with legs on all four sides or under, or without feet but with simple contacts (QFN); then, many others, often patent of some manufacturers and are named also from the houses using patented names. The monolithic integrated circuits are manufactured exclusively by producers who have designed and patented until the expiry of patents, then, the companies that designed them must publish the films used in the etching process and the patterns of their products so that other homes (second sources) can produce the ICs compatible. That is why, for example, an LM324 is produced, for example, by Texas Instruments, by ST or by National Semiconductors. ICs that are equivalent or compatible, have often part number similar to each other and rarely different, but in any case manufacturers publish tables of equivalence between their integrated and those of other major producers, or those

standards. Worldwide, an integrated product that comes from other manufacturer have a code base that is always the one, what changes can be letters or numbers that form a prefix or suffix: for example, are integrated as the LM723 or equivalent signed µA723 MC1723. Furthermore, the 4000 logic family is called, depending on who produces it, HCF/HEF4000 (ST or former SGS) TC4000 (Toshiba) MM4000 (National) MC144000 (Motorola). As for hybrids, have a limited and almost always standardized, saying with these words that each manufacturer produces its own, with its own peculiarities, have various shapes and usually appear as thin plates, possibly covered with resin, which are often seen on the components (all strictly surface-mount-devices) or

www.riparazione-notebook.net Tipical IC encapsulated in DIP case; DIP can be either plastic (civil-use components) or in ceramic material (for components of military or industrial degree). 58

directly as a template in the coating. The hybrids have the pins over one or more sides and can sometimes resemble the monolithic. There are also hybrid modules power, encapsulated in an epoxy resin black as that of the monolithic.

Scale of integration Since their birth, integrated circuits are been classified by their level of integration, it means by their complexity; starting from simplest, with few active devices, the technology has arrived today, proposing components that contain millions of transistors. To get an idea of the complexity of a chip, we list the classification complexity: SSI (Small Scale of Integration); is the simplest class, as they belong to the integrated operational and generally linear ICs, but also the elementary logic, and has some tens of components or logic gates per chip; MSI (Medium Scale of Integration); belong to the complex logic devices (counters, shift registers, arithmetic-logic unit) and has several hundred electronic components per chip; LSI (Large Scale of Integration); in this class we found microprocessors, microcontrollers and memories; devices which they belong has thousands of components per chip; VLSI (Very Large Scale of Integration); includes chips containing more than one hundred thousand members and is used in manufacturing memory of modern high-capacity and higher performance microprocessors and microcontrollers. Currently, in the notebook makes extensive use of various components: the processor and chipset are undoubtedly of VLSI, and LSI can be the bridge controller and USB, ethernet etc. The common logic is made with SSI technology.

Gender of integrated circuits Due to its nature as a microcircuit, the integrated may contain different structures, that can be more or less complete electronic circuits or independent, which realize individual blocks or entire autonomous systems, and, as any circuit, can be either analog or digital, low or high frequency, small or high power etc. The integrated split, like all electronic devices, into two kinds: analog and digital. Within each, then there are various categories, each of which is in turn divided into types. In computers it makes use mainly of integrated digital logic gates from simple to complex chipsets, microprocessors, or CPUs. Is not the purpose of this book explain the individual kinds and types of integrated, but rather to make a quick overview on them.

Operational Amplifier

In the whole analog integrated gender, the more interesting, for its characteristics and use that if it can do, is operational. It is an amplifier, ie a device that raises the voltage and current returning output as compared to present themselves at the entrance, whose particularity is that it has an input of the differential type, or two inputs which act opposite to each of the other: the voltage applied to the said inverting (-) is subtracted to the one applied to the noninverting (+). The operational amplifier amplifies the algebraic sum of voltages at two inputs, which is why he is named “operational”. The operational amplifier is used in audio circuits of the computer, but also as a voltage comparator in the power supply and temperature control of the CPU or the main power supply.

Linear voltage regulators Among the most frequently used in integrated electronic circuits are the linear regulators, which are used to obtain stabilized voltages starting from the main power supply; are typically three-terminal, encapsulated in a TO-92 and TO-220 case. Using them is simple: apply the input (E) starting voltage and the output (U) is taken that you want to get stabilized, the two are related to the common terminal (M). Oftentimes, in order to filter the voltages from disorders that may compromise the stability of the regulators, are connected between the inlet and outlet and mass and mass of the capacitors. The threeterminal regulators are typically those signed and 78xx and 78Lxx, according to the manufacturer that produces them, may be called µA78xx, LM78xx, etc. L78xx. The two x are meaning that to 78 must follows two ciphers which indicate the regulated voltage provided by the component: for example, 7812 regulator provides 12 volts. Moreover, the 78xx are in TO-220 and can deliver up to 1.5 amps (an enhanced in power version, named 78Sxx, provides up to 2 A), those in TO-92 are 78Lxx, which deliver 500 mA. The regulators of this kind have complementary, which serve to stabilize the negative voltages; connect to the same manner, but clearly negative on the branches. Among ICs linear voltage regulators, we can observe new series LDO (Low Voltage Dropout) the first feature of is low difference between output and input voltage; this regulator perform a low voltage loss across regulator, so is designed for battery-powered devices. LDO voltage regulator are, for example, Microchip MCP1725 and MCP1726, or LT1962 by Linear Technology.

Digital ICs A large family of integrated circuits, important equal to the analog, is comprised of the digital IC, this term all the chips that work with digital signals or containing blocks of Boolean logic (binary). They also belong to the microcontrollers Now, attention should be focused on the most simple ICs, which are the socalled “logic gates”: in a few words, integrated circuits containing components that perform the elementary logical functions, i.e. OR, NOR, AND, NAND, NOT, exclusive OR and exclusive NOR. These functions may be performed by electronic integrated circuits based on different technologies, i.e. families of transistor BJT (something, in this case, TTL logic, CML, or I²L) or MOSFET (CMOS, NMOS, HCMOS).

At first, that over thirty years ago, the logic gates and integrated with other simple functions such as flip-flops and counters, were made with circuits based on transistors and diodes or transistors only: the related categories of logic were called, respectively, DTL and TTL, TTL were developed many variations, including TTL-L (low) TTL-F or S (high speed) and TTL-LS (a mixture of speed and low power consumption). The TTL logic has been the first to be developed for two reasons: the high-speed in switching of bipolar transistors, compared to that of integrated MOSFET produced in these years, “held back” by the large parasitic capacitance due to the fact that transistors could not be much smaller; the relatively small size of the chips; the low voltage operation, needed to make circuits operating at only 4 to 5 volts. But the technology TTL had a defect: the large current consumption of the transistors and the input impedance of not quite negligible, since the BJT elements are current-controlled; also to increase the consumption of the TTL and slow down the switching, there was the fact that in bipolar transistor the transition from saturation to cut-off (interdiction) is rather slow. To speed up the switching was then developed technology Schottky (TTL-S) which provides a Schottky diode (precisely) between collector and emitter of the output transistor of the logic gate; the low voltage-drop of the diode causes the saturation voltage of the transistor remains at a value such as to allow a rapid recombination when switching interdiction. Despite to the introduction of the Schottky, the devices TTL consumed, however, too much current, and was then made of the series TTL-LS, e.g. gate based on Schottky TTL technology but with low consumption, that combines the properties of speed of the Schottky and low power consumption of the circuitry TTL-L. In addition to the TTL logic, bipolar transistors were realized in integrated CML (Current Mode Logic) and I²L, but, given the high cost and consumption especially significant, were only used in minicomputers, large servers etc. About for the MOS logic element, up to twenty years ago was a restricted part of digital electronics; was made with only MOSFET, typically enhancement mode N-channel, instead of the NPN BJT. This logic was later realized that in CMOS, in each logic gate which was composed of a complementary pair of MOS transistors: an N-channel and a P-channel. This allowed to obtain logic gates with very high input impedance and low output impedance (in the MOS, the output impedance is low only when the current is carried from the transistor, while when the same must pass from the load resistance is high enough). Apart from the reduced switching speed (due to non-negligible parasitic capacitance of the gate) and the size is not negligible, the main defect in the voltage of the MOS was necessary to send them to run, not compatible with the TTL because of the insulating oxide sandwiched between gate and channel is not allowed to obtain the threshold voltages of less than 5 to 6 volts. The same problem affect the CMOS. Over the years, technology has improved so much integrated MOSFETs, mainly due to the aging of photolithographic techniques, now make it possible to affect large areas even a few tens of nanometers and this is the possibility of using thinner gate insulating oxides, have allowed operate the MOS and CMOS logic voltages as 2 to 3 volts, then fit the TTL circuits and batteries and battery powered.

Since then, manufacturers have pushed hard to developing CMOS technology, the only one that could allow the realization of logic gates small and low power that enabled the birth of modern microprocessors and microcontrollers for portable devices and Personal Computers, but also memory chips that are in devices like MP3 players and digital cameras cards. Currently in production is that memory processors with 32 nm technology, where, i.e., a transistor measuring just 32 nm (0.032 milliohms of a meter). Coming soon see the light of processors and memories made with transistors the size of 28 nm. Discrete Logic The integrated more commonly found in electronic circuits, which are the basis of binary logic, are logic gates, counters, flip-flops, shift-register etc.. Briefly, the so-called discrete logic. Regarding to the TTL logic family, there is a 74xxx or the corresponding 54xxx, for military use or industrial use; the first work in environments where the temperature is between 0 and 70 ° C, while the second is due to harsh conditions (by - 55 to +125 ° C). For example, the integrated 7400 contains four NAND gates, the logic 7404 six inverters (NOT) and the 7474 is composed with two flip-flop. As for the CMOS, at least for the discrete logic ICs are those of the 4000 series: for example the quadruple OR 4001, 4081 four AND gates, the quadruple NAND Schmitttrigger 4093, the sextuple NOT 40106, the double flip-flop 4013. In the standard CMOS, as well as typical TTL logic are functions such as arrays and CMOS switches, which exploit the possibility of conducting MOS circuits such as switches when driven under tension. Then there is the series of CMOS TTL-compatible, which are the HS-CMOS, in short, the 74HCxxx: perform the same functions as corresponding 74xxx (for example, the 74HC00 is equivalent to the TTL 7400). Are fully compatible with respect to the voltage levels at input, while as regards the output fit, although not always to work at 5 volts; full compatibility with the TTL level input/output the damage the 74HCTxxx. On computers it uses a lot of the 74HCT373 and latch 374 and a buffer as the 74HCT244, 74HCT245 or transceivers such.

Audio amplifiers An important category of analog IC is the one that includes the integrated audio amplifiers, which consists of many devices, some of which are not always linear only, but mixed; includes components from a few hundreds of milliwatts to tens of watts, usually operating in AB class. In sound amplifiers family are located many types of integrated: the final power amplifier, headphone amplifiers, but also simple driver, that are components designed to drive power transistors which is given the task of giving to the load (loudspeaker) current they need. There are also complexes integrated circuits working in D or H class. Apart from the low power components, such as TDA2822, LM380, LM386N, TBA820 (which are supplied in DIP case) integrated amplifiers are encapsulated in cases that have a metal plate on a side to be supported to a radiator that allows dissipating the heat produced during operation. The audio amplifiers can make signals preamplification or drive speakers; in notebooks are used for both types: those that amplify weak signals are connected to the microphone

input (or to that of the line) and to the possible microphone integrated in the screen, while the final power driving the speakers located on either side of the case to spread the sounds, but also, through the appropriate jack on the headset. The integrated audio is always associated with the sound card (audio device) that are part of it.

Transistor arrays In the notebook, it make a wide use of integrated MOSFET, that is available in TSSOP case dual-in-line pin: widespread are the complementary pairs of Nchannel MOS and P, used to make the switch stage of switching power supply. Individual MOSFETs are used, in addition to switching, or even to switch power on and off the various stages of the notebook. Often these integrated SMD very small, which use the base or a metal plate on the bottom (to solder on special tracks of the printed in such a way that conveys the heat and achieve the electrical connection of one of the terminals of the drain or source) to dissipate the heat produced during operation. This is possible thanks to the fact that the MOSFETs have very low resistance Rdson, so even in strong currents dissipate little power: resistance of 0.001 ohms to 10, determine a power of only 0.01 watts! The MOSFETs are also found in array, that is integrated which also contain more than two connected with the source in common.

Figure 4.2 TSSOP case with 20 pins: is pratically a DIP case built to permit surface mount.

FPGA and PAL Sometime, in the computer makes use of programmable logic (PAL and FPGA): it is also very complex integrated circuits, programmable to perform specific functions instead of microcontrollers and microprocessors, or as a video unit, for example FPGAs can be used to image processing and then as a real GPU. The FPGA can be found practically only in square case BGA, QFN and similar. Main FPGA manufacturers are Altera and Xilinx FPGAs. The PAL array of logic, simpler and cheaper but equally useful for FPGA.

Cases for ICs The chips are encapsulated in cases each distinguished by a form and by a certain arrangement of the contacts (pins, pads); the most common is the dip (Dual In-line Pin) showing the pins laterally and can be of plastic resin or ceramic material, with possible carryovers or glassy metal. The DIP was created to mount the terminal loop, its development in SMD version, widely used in notebooks, the TSSOP. Are also widely used formats QFN (square or chip-carrier, if you prefer) TQFN etc., Which have a square case

surrounded by pins to be welded, which can be stretched or bent under the body. The case is most interesting large notebook chips, meaning that the northbridge chipset and southbridge, but also some CPU and GPU (graphics chip) is the BGA: in this kind of case the contacts are gold-plated copper disks that are joined to the pads of the circuit printed where the chips are mounted via solder joints or solder RoHS compliant, the welds are made by applying heat small balls of solder on the contacts of the chips, which are positioned very precisely, thanks to special steel jigs on which the alloy can’t join. Once applied to the balls, the chip can be supported by matching the balls to print them with the pads of the PCB and warming everything to get melting of solder alloy.

Figure 4.3 - Chip in carrier package: on the left, the VQFN with 20 pins (upper and bottom view) and

www.riparazione-notebook.net on the right the TQFP case (upper and bottom view) with 64 pins; as you can see, those cases have a metal plate on the bottom, that it have to solder to a pad on the PCB to function like an heatsink. 64

Figure 4.4 QFP case: is like a TQFP, but on the bottom side haven’t the metal plate heatsink.

Optocouplers An important category of integrated circuits is that of photocouplers, also called optocouplers or optocouplers; a photocoupler is a circuit, even very simple, which provides for the transfer of an electrical signal in the form of light, typically infrared, and consists of a sealed case, which prevents the entry and exit of the light, in which an LED is located directly on a photodiode or a phototransistor on the basis of, usually NPN. The LED is the input element, i.e. the one that receives the signal to be transferred, while the photodiode or phototransistor is the output element, i.e. the one which converts the optical signal into electrical signal. To understand the operating mode of optocouplers, must first know what they are and how they work photodiode and phototransistor. In Chapter 3 has already been explained the operation of the photodiode, and now you can describe what the phototransistor. The phototransistor is a BJT (Chapter 3) in which the base is facing outside through a window in order to be invested by the light or, better, by infrared. When the base receives light, the energy that the latter gives the free electrons from the bonds of the dopant atoms, electrons which, if the collector is positively polarized with respect to the emitter, and with a voltage of sufficient value, are sucked into the circuit-based manifold giving rise to a substantial collector current. Therefore, a phototransistor connected in common emitter mode, having the collector electrode biased as you normally would, with the base not connected to anything, when exposed to the light it makes to record an IC, like that recorded in normal biasing; if in series to collector we place a resistor, across this there is a voltage drop. Since the electrons makes free from light take time to recombine themselves, even after it is suspended the illuminance of the base, the phototransistor is a little slow to recover, and shut-down, or when switching from conduction to interdiction; for this, sometimes agrees connect the base to the emitter via a

www.riparazione-notebook.net Two kind of BGA integrated circuit: note the solder alloy balls on the bottom side. 65

resistor, which is intended to close the circuit of the junction. In applications where the transistor must pass abruptly flow from the conduction and vice versa, the resistance accelerates the transition, but has the effect of reducing the base current and thus the Ic recorded at constant light intensity, because part of the charges is anneals due to the closure of the base circuit and in any case does not remain on the basis but circulates in the resistance. Therefore, the latter should be chosen considering that the more high-value, the lower the switching speed but the higher is the Ic, while, conversely, low values speed, yes, the switching, but reduce the Ic. Operation of the photocoupler Directly biasing the LED, the light which it emits invests the photodiode or phototransistor, which goes into conduction; inserting the output component (i.e. a photodiode or phototransistor) in a special circuit, the current flowing in it represents the signal transferred optically. The optocoupler is not a linear circuit, because the LED has a characteristic of the first degree of proportionality between the voltage that is applied and the current running through it but also because there is no linear relationship between current and light emission, also , is not linear even the photodiode or phototransistor output. For photocouplers is used to define a parameter that represent the efficiency, i.e. the ratio between the current that must slide in the LED to have a certain current in the output component; the parameter is the CTR (Current Transfer Ratio, i.e. transfer ratio current) and that is: CTR = Iu/Ii where Iu is the current in the output device (for example, the Ic of the phototransistor) and Ii in the LED. Typically, a photocoupler consisting of an LED and a phototransistor (e.g. 4N35 or 4N25) has a CTR of 100% (1); one that has at its output a phototransistor and a common transistor connected in Darlington, also has a CTR of 200÷ 300% (2÷3). Therefore, the phototransistor is connected to a common emitter and the collector biased as you would normally not connected with the base, if invested by

www.riparazione-notebook.net Graphic symbol for optocoupler; this component is built from a phototransistor (on the top of symbol) and an infrared LED (on the bottom). 66

Figure 4.7 - Block diagram and pinout of a clock multiplier CY2300 manufactured by Cypress.

the light is used to record the Ic; entering the collector resistor, on it there is a voltage drop. Since the free electrons take time to recombine, even after it is suspended the illuminance of the base, the phototransistor is a little to recover, and cut-off current, or when switching from conduction to interdiction; for this, sometimes agrees connect the base to the emitter with a resistor. In applications where the transistor must pass abruptly flow from the conduction and vice versa, the resistance accelerates the transition, but has the effect of reducing the base current and thus the Ic recorded at constant light intensity, because part of the charges is anneals due to the closure of the base circuit and in any case does not remain on the basis but circulates in the resistance.

Crystal oscillator and clock multipliers One category of integrated very interesting as regards the computer, and then also the notebook, is that which groups together the clock generators: they are components that produce the signal base and multipliers (clock multiplier) able to raise the frequency, when necessary to do so. The generators are complete based on a quartz oscillators, which are available in integrated form and usually have four pins; externally appear as quartz, which contain only a crystal and an electronic circuit capable of oscillating at the frequency of the latter. These hybrid microcircuits are extensively used in various stages of the computers, which can serve not only to provide the clock of the CPU and video cards, converters but also of sound devices, communication devices (buses of various types) and many others device types. The clock multipliers, however, are specific logic circuits which are put in cascade to the generators of quartz and are able to multiply the output frequency of up to hundreds of MHz, starting from the standard value of 32,768 kHz universally adopted by the

generators of clock. The multipliers derive clock signals for the processor (at least the basic clock, because then the CPU multiplies internally of a certain factor) and the GPU, but also for the communication interfaces, the internal buses (for example, the I²C-Bus used in the dialogue between the main power supply and chipset) and memories; multipliers generally operate on the basis of the PLL (Phase Locked

Figure 4.8 Block diagram of NB3N502 clock multiplier, manufactured by ON Semiconductors.

Loop, i.e. phase-locked loop) that are devices able to synchronize with a frequency and generate a multiple. May also be composed by counters or discrete logic suitably configured to produce two, three, four or more output pulses for each clock pulse received at input, but the main technique is that based on the PLL. The mainboard laptops and computers in general, the clock multipliers can be recognized because they are close to the crystals or the crystal oscillator and are almost always produced by Cypress or ICS, are examples of the Cypress CY2300, CY2308 on, but also the CY22800. Figure 4.7 shows the block diagram of the integrated internal and pinouts CY2300. Figure 4.8 illustrates, instead, the block diagram of another integrated clock multiplier: it is the NB3N502 by ON Semiconductors.

CHAPTER 5 PC MONITORS In notebooks PCs, where images and text are visualized through digital displays in which the image is built polarizing one by one the points of a matrix composed of cells containing liquid crystal; the same monitors, but less thin and placed in cases it can be placed on the table, are those that are now combined with all desktop computers, as far as the CRT screens have been banned. The monitor (LCD stands for Liquid Crystal Display, or liquid crystal display) consists of the following parts: the synchronism discriminator; the video component digitizer; the pixel positioner circuit; the liquid crystal panel. The discriminator is a circuit that extracts from the video signal RGB sync signals; sends pulses of line and the logic of the framework that provides for the placement of dots on the screen. This logic is very complex and makes use of a microcontroller, microprocessor, or a device for DSP (through digital Signal Processing) because it must, synchronizing with the horizontal pulses, put in their place all the points corresponding to the portions of the video component contained in each row. Engaging with the pulses of the framework, the same logic must separate the signals corresponding to a half frame from those of following half-frame. The digitizer is a video component of the analog/through digital converter which, by means of special circuits separators, come the individual portions of the composite containing the information on the brightness and the possible chromatic hue of individual points. The reading and conversion in numerical value of the video signal occur with extreme rapidity (the sampling frequency is at least 10 times that of the composite). Each time a conversion is performed, the corresponding numerical values are placed in a memory of the RAM type, from which they are then taken to be sent to the positioner circuit of the points, or to manage the screen. This circuit, substantially controls the dot matrix contained in the liquid crystal panel, activating for each pixel row and column corresponding, in practice it will be scanned, before activating the first row and in sequence, one at a time, the columns from the first to last, then the second row, repeating the sequential activation of the columns and so forth. It thus proceeds until the last of the lines, when the sequence resumes from head; such a sequence of reconstruction is performed a number of times per second equal to Hz refresh rate, then 50 if we talk about 50 Hz, 60 if the refresh is at 60 Hz and so on. Since the image on the LCD screen is not built in real time, that is directly on command of the video signal (as in the CRT) it is possible to reassemble without interlacing; this means that before composing a complete picture of the logic waits and analyzes the signals constituting the two fields that comprise it, then stores them and reworks them, then puts the various lines in the exact sequence and sends them to the LCD screen to reconstruct the image. Interlacing (or interlace, if you prefer…) corresponds to compose the image with a rapid sequence of two halves of the image, constructed by activating a sun even rows (and columns in the usual rapid succession) and the other activating only the odd lines; making this task more than 25 times per second, the eye does not detect the

interlacing and always sees pictures integers. The vision interlaced in fact allows to reduce the switching speed of the individual pixels of the matrix LCD, which is very useful because the liquid crystals are relatively slow; interlacing also reduces the bandwidth required by the video signal and thus facilitates the task of the circuits that generate video signals (those of VGA) and amplifiers who treat him. In the case of vision interlaced, refresh rate refers to the half frames tracked, while if the image is not interlaced, it corresponds to the complete frames drawn in a second. Note that the timing discriminator and the digitizer component video only serve in the LCD monitor desktops that have VGA input, or in the notebook which does not have the video chip outputs in through digital format, but has the only VGA output, sorted by a switch to the 15-pin connector or to the display. For PCs have the video device equipped with a through digital output, the two blocks out above will not necessary: the through digital outputs directly control the logic of the screen. The same applies to the PC monitor fixed to HDMI or DVI through digital.

The liquid crystals displays The viewer of the LCD monitor of the laptop is formed by many small cells

Figure 5.1 Composition of a tipical liquid crystal display and it behaviour in idle state and when is under polarization voltage.

that, in elemental form, are composed of a certain amount of liquid crystal between two glass plates; the set is laterally delimited by sealed glass or epoxy adhesive sealant. The liquid crystal is a chemical with a crystalline structure which at room temperature is presented in liquid form. The liquid crystal display LCD is used in the type of cholesteric or nematic, but currently the most widely used is the nematic. In the inner side of the glass surfaces, are made the electrodes obtained by the deposition of conductive material (carbon, for example), not to hinder the vision, the material is quite transparent, so although see, does not disturb too much. The most interesting feature is that the liquid crystal, which is subjected to an electric field, it becomes opaque and does not pass the light from the glass on the back to the front; thus, shaping the electrodes so that they have to draw the shape of the figure, an appropriate polarization allows you to see the dark parts you want to form the image.

The liquid crystal has the crystal structure of helical form, is composed of many overlapping thin strips, which normally all have the same orientation. Subjecting the structure to an electric field parallel to the vertical axis, the strips revolve, from the base to the vertex, 180 degrees; effect of this, the crystal from transparent becomes opaque because the light is no longer able to cross it. Normally, the polarization is given in the form of alternating voltage, the frequency of some tens of kHz. More exactly, the liquid crystal is characterized by having molecules oriented so that when light passes through it follows the orientation. Normally, passing through the liquid crystal, the light is rotated by 90°. When the same crystal undergoes the effects of an electric field, its molecules are arranged vertically , and then the light passes without undergoing rotation. Outside of the two surfaces, there are two further layers of filter, arranged at 90° to each other, that polarize light. In resting conditions, the light coming from behind passes through the first filter and is polarized, passes through the liquid crystal (where it undergoes a 90° rotation) and finally through the second filter and exits from the front glass. Instead, if the crystal is subjected to an electrical voltage, the light polarized by the first filter passes unchanged to the liquid crystal and is blocked by the second filter, and then does not come out from the display. The first LCD graphics were passive matrix and were formed from a glass substrate with surface metal oxide very transparent, equipped with a grid of electrodes needed to activate the individual elements of the screen on the substrate was deposited a film of a polymer with a series of parallel grooves made to align the liquid crystal molecules. A second layer, analogous, formed from glass, complete polymer film of alignment, was overlaid ( and with spacers to maintain a uniform distance from the bottom layer). The two were welded with an epoxy resin to the sides so as not to leak the liquid crystal. Outside of the two plates were finally apply layers light polarizers. In the LCD graphics orientation of the alignment layers varies from 90 ° to 270°, in function of the total rotation of the liquid crystal between them. The LCD displays are made in three structures, which are the transmissive, the reflective and transflective. The first requires that the light reaches the observer that the design formed by the liquid crystal leaves pass from the back; in the second the back is leaning on a white sheet or mirror, so as to reflect the light in areas not polarized and therefore clear. The third combines both techniques, ie the bottom of the display is leaning on a white sheet illuminated posteriorly; thereby reaches the observer is the reflected light, both the incoming from the back. In the liquid crystal monitor the preferred solution is the transmissive: the display is supported posteriorly to a plate of plexiglass, which rests on a silver sheet; foil plexiglass is illuminated from the side or above and below by neon tubes that, thanks to the horizontal propagation of light along its structure, make it appear evenly lit. The image, already visible (although dark) in the daylight, is made evident and clear from lighting produced by plexiglass. Developed initially to dial digits and letters (used in quartz watches and displays of modern measuring instruments and control, as well as in many consumer devices), LCDs were then made using the dot matrix for displaying images. Just the realization of the LCD dot matrix allowed us to have the monitor of the notebook. Until about twenty years ago and monochrome LCDs were low resolution, the field of personal computing and the TV’s have pushed the industry to study high-resolution color display. The problem of the resolution has been solved honing construction technologies in order to reduce the size of the points while that of the color has been solved preparing

matrices, in which each point is formed by three sub-pixels, ie three elements placed each in correspondence of a color filter. Substantially, in the color display each point has a red filter, one green and the other blue, in line with a portion of the liquid crystal, because the point becomes red polarize the areas of green and blue, so that the corresponding light does not pass, and that the observer is reached only by the red com

Figure 5.2 Structure of a color LCD cell: it can see three optical filters for a single pixel, each one of this manage a subpixel.

ponent. To see the blue light are polarized green and red and green are polarized to get the red and blue. To obtain the other colors making appropriate combinations (for example, purple is obtained obscuring only the green and leaving free the pixels of red and blue, so that they can be traversed by the light). The white point is obtained by letting the light from all three sub-pixels that compose it. To increase the contrast, worsened by the fact that the image has no light of its own but is backlit, the glass plates which delimit the liquid crystal are transparent yes, but dark and unclear. This reduces the brightness but gives greater prominence, especially to color images. The traditional LCD display is relatively slow in switch from consecutive images, because the time of rotation of the liquid crystals due to the polarization and the return to rest when the same polarization is removed, it is not negligible, the effect is seen on the display when displaying an object in rapid movement, which is followed by a shadow. The response speed of LCD is defined by the response time, or by the following two times: rise time , namely that used by the crystal to rotate from the time in which the crystal receives the bias voltage; fall time, ie that employed by a helical structure to return to rest after the interruption of the bias voltage. Typically, the times are of the order of a few tens of milliseconds (although in the panels of the most recent production is also drops below 5 ms), then a quick calculation done considering the number of points constituting an entire television image already gives an idea the slowness of the display. As a workaround, draw a whole picture at a time and fly together all the points of a line, giving the corresponding data columns. However, generally, a pixel must be able to turn on and off within 1/60 second (so much is the typical refresh period of the LCD screen) so as to maximize the fluidity of moving images; considering what has been said earlier, ie that all points of the screen are turned

on together, the response time should not exceed 16 ms. In the LCD display recently produced such a requirement is fully satisfied, so that moving pictures aftermath damage only if they are very fast. The response of the LCD with the driving system of a passive matrix just described is very slow and not able to follow fast changes of the content of image represented. Best response times were obtained by organizing the screen into two parts and performing the refresh independently for each of them, these screens are denominated DSTN (Dual Scan Twisted Nematic ). The luminance level of each pixel is obtained by varying the voltage applied to the liquid crystal, so as to modulate the angle of rotation and consequently the amount of light that passes; this allows to obtain about 64 levels for each color. To obtain a greater number of shades of color, techniques have been developed according to which the levels are changed in the course of three or four consecutive refresh image. In this way are obtained accuracies next to 256 levels (8 bits) for each of the primary colors, similar to those TrueColour (24 bit, 16 million colors) provided by the CRT.

The TFT display The first LCD had a limited view about 90°, while the extension of the horizontal and vertical viewing angles permitted by the monitors of modern laptops was obtained by the technique TFT (TFT means Thin Film Transistor) which consists in a set of three in each pixel transistors, which control each sub-pixel, which is why the TFT display is also called “active matrix”. The structure thus realized allows to control at each point of the screen, obtaining a thickness smaller than the display (due to the fact that there are fewer lines of activation) and thus a better view (because the light comes from an area less deep); also allows a higher switching speed of the liquid crystal from the position of darkening to that of passage of light ( the response times are also of the order of 5 ms). TFTs are lighter and faster in the transition from transparent pixel (light passes) to opaque (light is blocked) but much more complex (requires a VGA 921,000 transistors, while an XGA 1024x768 employs 2,359,000 points transistor). The quality of the TFT were initially diminished by a defective display due to the imperfection of the construction technique, the complexity of which is not allowed to create matrices with 100% of the pixels working: in practice, some points of the matrix appeared white or colored because the transistor correspondents were not working and did not allow the blackout . The pixel or subpixel therefore always remained transparent and let light pass through, appearing as bright dots that disturbed vision. To overcome this drawback , some 10 years ago, it was developed a TFT which used a new type of liquid crystal in which the molecules are vertically aligned (VA, vertically -aligned ), in this way, when there is no applied voltage, the image is black, while applying the polarization of the molecules are arranged horizontally and the light passes through the crystal. This improves the quality of the black and the viewing angle, which reaches 140 ° in all directions, but also the contrast. So, today it can have on the market zero-pixel defective displays; otherwise, some traders sell some TFT displays having some defective pixel, proposed like a second choice computer parts. Furthermore, technology continue to product displays having defective pixel, but improvement in industrial processes allow to obtain more zero-pixel defective displays than in the past.

The evolution of the VA LCD technology is the one called MVA (Multi-domain Vertical Alignment), which determines the rotation of the liquid crystal molecules in multiple directions for each cell instead of only in one direction as in the basic technology. So, looking at the screen from various angles, the vision is relatively uniform, while in the standard screens varies between light and dark based on the alignment of the observer relative to the orientation of the molecules. The MVA technology has led to an even wider viewing angles (160°). The matrix is composed of many cells (pixels) each controlled by a field effect transistor (MOSFET) of which the gate is connected to the driving circuit of the lines and the source to that of the columns. To activate a subpixel , will provide the appropriate signals (logic levels) to the row (gate) and the column (source) of the corresponding transistor , to control a pixel activates a row and three columns (RGB signals) of the same pixel. The amplitude values of the bias voltages supplied to the transistors of the cells determine the percentage of light transmission through the panel and the backlight filters red, green , blue, and then the hue of the corresponding point . Basically, the circuit which drives each subpixel is formed by a transistor and a capacitor (Cs) as the output load of the TFT. The circuit is also part of the virtual capacity of the liquid crystal (Clc). Applying a pulse of about +20 V to the gate line, the TFT is turned on, the Cs and Clc are charged and the voltage on

Figure 5.3 - On the left, electric diagram of TFT cells (note parassite capacitance Cs and

Figure 5.4 Building of a modern LCD panel, equipped with backlight based on CCFL lamp.

the specific subpixel (indicated as electrode pixels in the Figure 5.3) rises to the level of the signal applied to the data line. The TFT turns off when the gate voltage drops to -5 V. The capacitor Cs has the function of maintaining the voltage on the pixel until the next scan. Since the liquid crystal must be driven with alternating current , and this is usually achieved by reversing the polarity of the voltage applied to the pixels at each change of the framework, in order to avoid flickering of the image. The gate and source electrodes of each sub-pixel are used in sharing lines (gate lines) and columns (data lines) of the matrix, but each sub-pixel can be addressed individually without interfering with those neighbors. The operation of a LCD is based on the progressive scanning of the gate lines by applying, for each row of the image, the appropriate signals to the data lines. In the majority of TFT display, light is generated by cold cathode fluorescent lamps placed behind or to the side of the screen. The filters red, green and blue for each pixel are so small that the eye perceives light that passes through them according to a single color tone resulting from the sum of the three primary components, namely the sum of the light intensities resulting from the passage of light through the subpixel. In a display with 16 million colors, each subpixel can be driven by a signal that has 256 possible values. Each of them corresponds to a value of the intensity of light passing through the sub-pixel, the almost total opacity of the liquid crystal to its maximum transparency, filtered through the screen of colored subpixels.

A complete LCD panel, viewed from the back: you can see the control circuitry and the connector LVDS for the flat cable that leads it to the mainboard. It is clearly visible the wire fluorescent lamp backlight.

OLED displays OLED (Organic Light Emitting Diode) is a brand new type of display that can generate their own light like the plasma display, but running at low voltage and with a consumption comparable to that of LCD. Its introduction in the field of laptops dating back about a year ago and even today there are few notebooks equipped with OLED, currently still too expensive. The definition of organic LED comes from the fact that the system is based on small cells made with organic semiconductors that emit colored light. OLEDs have a wide viewing angle and are very light and thin as LCDs. The OLED is very recent, in fact, have been proposed in 1998 the first color products, although characterized by limited performance (800 x 600 pixels, 300 cd/m² luminance, contrast ratio of 300:1) in little more than 10 years, we have gone from first small display to the modern active-matrix displays. The elementary cell of an OLED consists of a stack of layers of electrically conductive organic material comprised between two electrodes: an anode (positive) and a transparent cathode (negative) metallic, or, in the structure with the emission from the upper zone, by a semitransparent cathode and a metal anode. There are also display active matrix OLED (AM OLED) whose cell is the set of a metallic cathode and an anode organic or inorganic, all supported on a substrate that contains the circuits of activation of the individual pixels . As in the common LED , current flows because free electrons and easily moved by a weak electric field can go to fill gaps in the structure of the material with a lower value . When a cell OLED is applied a voltage of a few volts , negative on the substrate and remain on the lower layer (cathode), electrons depart from this and go to fill the gaps in the organic layer connected to the anode, yielding the energy supplied to them by the electric field to move them, and this energy is released in the form of electromagnetic radiation with visible length (electroluminescence) . In the graphical version, OLEDs all have a matrix of points and each pixel in the matrix component is activated by a pair of pins arranged in rows and columns: just like in the LCD. OLEDs are candidates to become the displays of the future, at least for applications where you need to have bright, high-contrast images, the ability to produce them in a transparent version, will generate combined image display systems and

lighting, in practice, the same display can show images of the television or be solid with all points of the same

Figure 5.6 Building of a typical OLED display cell.

color, thus forming a real lamp or a light furniture that can provide any solid color. But it does not end here: as the emission of light occurs on the front, there is no reason to apply a transparent OLED in a window or a glass wall that divides the two environments: in this case, the light will be directed into the room which is facing towards the front of the viewer. Another important feature of modern AM OLED display is the ability to enable and disable the pixels more quickly than possible with the TFT , for this reason , the OLED technology is able to provide the best results in terms of quality of vision of moving objects. The performance of OLEDs are now at the level of those of the best LCD on the floor of the contrast (even 100,000:1) with regard to the brightness (also 600 candles/m²). The shims can fall below the inch and the resolution also comes at 1920 × 1080 pixels, more than suitable in the case of movies in HDTV ( high definition TV ). Similarly to the LCD, there are a passive matrix OLED display and an active matrix; in a passive matrix display , a thin layer of polymer is applied to a substrate, typically glass covered by a structure of lines (forming the anodes) obtained from a layer conductor deposited on the glass. The cathode lines are applied in a direction perpendicular to those of the anode, with a similar method. A recent innovation is represented by LTPS technology (Low-Temperature PolySilicon) which provides a substrate in polycrystalline silicon is capable of spreading the current in a more uniform way. The structure of the organic layers and anode and cathode is designed in order to optimize the process of recombination in the emitting layer, and then the luminous flux. By suitably choosing the materials constituting the various layers, the entire structure can have the thickness of only a tenth of a millimeter. To activate a point or a sub-pixel (in color systems) applies a suitable voltage to an anode line and, as long as the same remains powered, are polarized (connected to the negative power) in sequence and one at a time all the lines corresponding to the cathodes. Then comes the line is activated anodic next, and

once again you make a scan of the cathode, then it repeats the last line of the first anodic and then start over. In the case of active matrix OLED display, a transistor structure is integrated on the substrate of the display, there is usually a pair of transistors for each pixel. These transistors are connected in sequence to the lines perpendicular anodic and cathodic and are able to “hold” the active period of each pixel until the next scan. The active matrix OLED displays are more complex and therefore more expensive, but offer sharper and brighter images than those achievable by passive OLED.

E-ink screens It is of special viewers that have made their debut with the e- book reader. The e-ink technology, or electronic ink or e-paper (electronic paper); such displays were invented in 1996 by Joe Jacobson, founder of E-Ink (www.eink.com) and are so thin and flexible and are similar, in appearance, to a printed sheet. The e-ink reflects light like an ordinary sheet of white paper absorbs the inkblack. The display is composed of two plates (one of which is transparent), closed laterally, and between which is located a liquid substance containing tiny spheres electrically charged; in each of the microspheres, and positive half is colored in black, while the other half is negatively charged and is white in color. Applying an electric field to special electrodes on the surface of the plates, it can guide the balls so that they appear white or black; in other words, by applying the positive polarity on the outer pane (the one from which the observer looks at ) the balls are oriented with the negative half that way , and since the negative hemispheres are white, the points positively polarized the display is blank . If you apply the positive polarity on the inner pane and negative on the outside, from the outside looks half black (positive). The e-ink technology allows to realize thin, flexible media, since the structure ball is not altered by twisting or bending, so it is ideal for devices to carry, for example, in the school folder. But what really makes it unique e-ink technology are two characteristics: the first is that by placing the balls perfectly possible to represent a printed sheet, because the image (photo or text) is made up of points, just as with a printing ink-jet, laser or in typography; in e-ink display, similarly to what is done in printing machines, an area is much darker than the more dense are the points blacks and vice versa. No less important is the fact that the e-ink display is the only virtually zeropower: being based on microspheres that sit idle once oriented, requires electricity only when you need to polarize the plates to guide the spheres themselves and then only for change the contents of the screen. The contrast of a typical e-ink display is 7:1, while the viewing angle is 180 degrees; the response time (ie the rotation of the sphere from the black to

Figure 5.7 Grey-scale e-ink display: Panel is quiet flexible and requires a few of electrical power.

white) is around 700 ms (in mode to grayscale) and about 250 ms in black and white. Since they are not backlight, the e-ink display can not be used for TVs and monitors, but they are ideal for reading books, newspapers and other documents in the light of the day, and indeed, the very absence of proper light assimilates them to print and allows you to watch them for hours without straining your eyes.

LCD backlighting The liquid crystal display is passive and that used in notebook type is transparent, so it requires a backlight, which can be obtained in various ways , ie with a sheet electroluminescent applied behind, with a CCFL (cold cathode) lamp which diffuses the rear light through a sheet of plexiglass, or with LEDs that light always sheet of plexiglass. The electroluminescent sheet works such as neon and compared to this has the advantage of being able to be positioned directly behind the LCD, and then to illuminate with uniformity occupying very little space; instead when backlit with fluorescent tubes, these must be placed along one or both sides LCD and their light must be distributed through a plexiglass plate 3 to 5 mm thick, in practice it exploits the fact that this plate laterally illuminating the light spreads evenly (unless there is no distortion in the material) or more less in the entire surface, which then appears lit. The electroluminescent foil technique was soon abandoned because the leaves were limited compared to that of fluorescent tubes. The tube or neon lamp, is a discharge lamp, but the cold cathode type: consists of a thin glass tube filled with inert gas (neon or mixtures of neon and xenon) whose inner walls are coated with phosphors; inside the tube, at one end or the two opposite ends there are two electrodes. Applying a sufficiently high voltage , an electric discharge between these shell,

due to the ionization of the gas contained in the tube, the phenomenon propagates rapidly to the rest of the gas and causes the production of photons (particles of light) in the ultraviolet, that investing the phosphors do they produce white light. For the initiation of the download using the inverters, which produce voltages even 200 volts. Nowadays, manufacturers have experimented widely based alternative lightemitting diodes, in practice it uses a method similar to that of fluorescent lamps, except that in place, to illuminate the side of the sheet of plexiglass, is a row of LEDs. The LED control is realized with low-voltage current regulators, but consume a fair power. The main advantage is that the adoption of LED backlighting system lasts much longer than the others just described, being able to work for 50 to 70.000 hours corresponding to 15 to 20 years, of course, as long as you do not failures before the regulator circuit. In addition, LEDs do not involve problems related to the disposal of electronic waste fluorescent bulbs, which contain dangerous pollutants two elements: the phosphors (in the inner lining of the tubes) and mercury (the latter in the cathodes). With LEDs can also create displays in which the pixels are working in sync with the backlight, consisting of light-emitting diodes red, green and blue: when the pixel must appear red light only red LEDs, blue when it should be just the blues and when the red light should appear to control only the red diodes. This can be achieved thanks to the high switching speed of which they are capable LEDs and allows to obtain color display without dividing the pixels into three subpixels, but simply using a single cell point, which simplifies the matrix (although complicate the backlight control) and allows to considerably raise the resolution of the image, since each pixel should not necessarily be composed of three subpixels and therefore may have dimensions smaller than those of a single-pixel LCD. On the opposite side, this technique slows the representation of images in motion, as for composing each color point takes three steps in sequence, then the response time is tripled. Backlight control In the old notebook backlight was turned on with the computer , but then, for the sake of saving energy and thus to increase the life of the battery, the power supply or inverter control was handled by the chipset, in order to moderate it or turn it off when the PC is not being used. The backlight control with power-saving function by the chipset is carried out in two ways: suspending the synchronization signal, in this case the DC/AC inverter works in dependence of the chipset, in the sense that it does not generate the clock signal (oscillator has not) but is activated from the one sent by the chipset; by means of a logical level (/EN, ie Enable) which activates or deactivates the oscillator inverter. The control module of the display for notebook includes a DC/DC converter that provides the various levels of DC voltage to control the liquid crystal , the control circuit and those piloting of columns and rows, a DC/AC inverters that provides the high voltage to power the cold cathode fluorescent lamps (CCFL) that provide the backlighting. In the case of the LCD display with LED backlight, there is also the DC/DC converter (you can see on the inductor core that appears on the electronic board ) to power the LED.

In notebooks with LED backlight or CCFL, typically the motherboard sends, via the internal monitor connector, data signals to the display itself and those for controlling the backlight, as well as, of course, to the feeds, which usually are two: 5 Vdc for logic (controller of the array, the power supply for LCD etc.) and from 12 to 20 V for the power supply of the backlight. In some notebook of the past, the connectors were two distinct, one for data and one for the backlight control. Regarding the data, for some time now it adopts the standard LVDS (Low Voltage Differential Signal) that is based on the sending of the information to the display using various channels (also 6) TTL serial 0/3, 3V or 0/5V (each with data and clock signals) which travels along portions of data, this form of transmission mixed serial/parallel allows you to restrict the conductors but ensures a high data-rate, since each data channel carries a portion of the overall data constituting the image to represent. The speed is set by the high resolutions and high refresh rates (refresh rate or frame rate: this is the equivalent frame rate of CRT monitors) that characterize modern monitors, where high definition has taken over. A characteristic of the data channels are differential LVDS is that, in the sense that each carries signals on two wires referring to the common ground, but the signals on the two wires are opposite phase: when one is positive, the other is negative; this allows to obtain voltages amplitude equal to twice that obtainable from a data channel unbalanced (ie constituted by a signal referred to ground) and thus a greater immunity to noise and a higher signal/noise ratio. The raising of the signal/noise ratio can reach very high speed communication lines can not be obtained from data unbalanced due to the level of electrical noise that is superimposed on the data signal. Regarding the backlight control, the relative connection shows these contacts: positive power supply (12÷20 Vdc) backlight (CCFL inverter or DC/DC LEDs); common ground and power signals; Enable, ie logic level that enables the backlight; clock to govern the final stage of the inverter; PWM, ie the pulse width modulated signal, which allows you to modulate the power of the lamps or LED backlight and then, as well as to vary the brightness, allows you to lower it in standby or when requested by way of energy saving. In laptops a decade ago it was easy to find different solutions, each taken from one or more brands, but today we tend to standardize, so that in the modern notebook computers, as a rule, the contacts that come to the inverter DC/AC or to the control circuit of LED backlighting, there are only four, namely positive power, common ground, Enable and PWM. The Enable signal controls the switching on or off, while the PWM determines the variation of brightness. The inverter or the control circuit of the LED is always powered , but with the Enable off (usually it is active high logic level ) remains in standby mode, turning off the backlight and consuming very little power. Figure 5.8 shows the portion of the circuit diagram of a modern motherboard notebook, where you can see the lines from the connector to the monitor reaching the flat cable that leads to the monitor itself.

LCD touch-screen It is that viewers are a complete user interface, in the sense that also act as monitor, keyboard and pointing device, are used mainly in the Tablet PC, handhelds and PDAs. To be possible that a screen can detect when and where it is touched, above the LCD panel structure it applies a coating that can works with two techniques: resistive (the first setup) or capacitive. The touch-screen resistive type bases its operation on the fact that pressing on the screen you create a contact between two electrically conductive layers, layers located on a transparent film that is in front of the LCD itself. The device detects the contact point by processing the data on the resistance measured between a vertical side and a horizontal. The capacitive touch-screen instead relies on the transfer of electrical charge from one plate , which is an electric contact in a film that covers the screen, and the earth: When you touch the screen, there is a flow of electrons is detected

Figure 5.8 - Circuit portion referred to signals that comes from LCD connector of a notebook PC: it can see LVDS data channels, power supply lines for LCD circuits and backlight circuits, and also power-on and control signals for backlight.

Figure 5.9 - Cross section of a resistive sensor used in touchscreen displays: under superficial protective layer, a pair of electrodes are joined in different amount depending on insert deformation, that brings that closer in more o less extensive area. The base is rigid to sustain structur under the compression.

by means of sensors positioned in each corner of the display, so as to estimate the coordinates of the point of contact. On the level of visibility is preferable to the capacitive system, given that the film of resistive reflects a little the light; as to sensitivity, in resistive pressure is essential to interact with the screen and it is possible to use fingers (even wearing gloves), nails, pens etc. The ability to use the nib is very important when you have to compose letters or written using the screen keyboard, as in PDAs or Tablet PC. The capacitive system has however the disadvantage of requiring the touch with a conductive object and then with the fingertips (nude), which limits the minimum size of objects or buttons on the screen that can be activated (as opposed to the resistive system, accurate least as much as the pixel resolution of the LCD display). It should also be said that the resistive system operates in a temperature range of more extensive and better withstands the moisture, while the capacitive requires a minimum of moisture in the air to facilitate the transfer of electrical charge; also when the environment is too cold damp or condensation prevents a clear position of the touch and sometimes arbitrarily moves the pointer.

CHAPTER 6 DC/DC POWER SUPPLIES In PC and Mac laptops, the voltages required are obtained by now practically only by switching power supplies, which are an AC/DC to transform the alternated voltage network (typically to 110÷240 Vac) in continuous low voltage, and some DC/DC circuits necessary to convert the latter low voltage into the various stages of computer; AC/DC power supply is usually external (albeit in some old Compaq notebooks AC/DC was internal) while the DC/DC are all within the notebook, on the mainboard and in additional cards. In this chapter we have referred to the structure and operation of the switching power (also called “switching”). The switching converters they are preferred to linear power supplies because with the same output power suffer of less energy losses in transistors that have task of supplying current to the load; power losses causes overheating and large consumption, and agrees to increase power supply circuit dimensions. Excessive consumption stems from the fact that the active components used to stabilize the output voltage hold “on their backs” the weight of the voltage drop, which is the difference between the voltage to be given to the load and that of departure; fact the transistor operating the adjustment variables dynamically behave as resistors, which increase its value when required little current and the decrease in the opposite situation, namely when it increases the current demand by the user. In applications such as power supplies in output voltage, the problem can assume dimensions are not negligible.

Switching power supplies In the PC, to switch from alterned current by network to direct current, but also from a DC voltage to another, is used for switching power supplies, otherwise simply named switching (or DC/DC converter). In them, the active elements that must supply the user does not conduct in a continuous way, but pulsed, and the value of the output voltage then depends on the average value, over time, of the pulses themselves. The same applies to the current. The resulting advantage lies in the fact that the power dissipated by each transistor is practically the only one to supplied to the user; dissipation, or the loss of the switching device, is minimal, and corresponds to the product of VCE saturation for the current that crosses transistor, and the whole compared to the duration of the pulses in each switching cycle. First you need to explain why switching have a negligible loss; defined yield of a generic circuit that must make a power conversion ratio: Pe = —— Pc where Pe is the power output and Pc that consumed. While in linear power supplies the power loss (the difference between Pc and Pe) is directly proportional to the output current and the potential difference between input and output, in those switching it operates by varying the parameters of the power. In other words, a switching functions as the transformer: to obtain a high voltage from a lower, transfers the power by varying the characteristic parameters, which transports the electricity itself, unlike what makes the linear regulator, which is limited to retain the power that must not go to the load.

In linear circuits, especially in those with variable output voltage , you can get to lose the transistor up to 100%; also considered that in operation in common collector, a BJT can amplify in current until the VCE drop remains higher than 2 to 3 volts, the efficiency can never reach the maximum, so even with the lightest load, is always below 90%. In switching, however, performance exceed 90% in any load condition, that is, the loss is virtually constant from the minimum to the maximum output voltage. In short, if the feeder linear yield is inversely proportional to the output current and directly proportional to the output voltage, in the switching voltage is independent from and linked exclusively to the current supplied. To ensure the minimum loss, switching power supply makes use of transformers or inductive elements, at least, switching in a broad sense. This clarification is unavoidable because the switching devices are part of the family of DC/DC converter, which brings together all the circuits which convert a DC voltage into another of different value or polarity, using the technique to switching. A switching power supply is a DC/DC converter, but a DC/DC is not always a switching. switching power supplies; take the input voltage from another power supply, linear or switching; when they have to work with the electricity distribution network are preceded by an AC/DC adapter, or a rectifier with capacitive filter; switching regulators, are similar to the previous but provide a stabilized output voltage, if the value of variable at will; inverters and voltage doublers. Generic switching power supplies and switching regulators play on the parameters of the electrical power to optimize the yield, while inverters and voltage doublers are united only by the fact of turning the tension in converting the continuous pulse and pulse DC component. A parameter applicant in the study of switching converters is the duty-cycle, that is the relationship that exists during the period of the waveform which determines the switching of the transistors of the converter, between the pulse duration (d) and the same period (T) length: DC = d/T When the pulse lasts half of the period, the wave in question has a 50% dutycycle; in the case of periodic voltages with pulses in step (rectangular) wave takes the name of “square”, because each pulse, drawn on paper has a square shape. The duty-cycle allows to evaluate the average value of a variable component in the entire period in the case of switching devices allows to understand how much energy, of the total outlet from the generator, transfer to the user.

Unregulated DC/DC converter It is those that are commonly said switching, even if the term DC/DC converter defines not a type but a family of circuits that includes the converter transformer and the winding inductance. The two types, while being structurally different, are joined by a common feature: in both played on impulses in order to transfer more or less power to the load; in other words, the power supply uses devices that do not limit current produces on the, but give pulses whose width is proportional to the power to be delivered. Here because they

allow a considerable saving of energy and thus a high efficiency. Transformer converter In its simplest form, consists of a pulse generator capable of obtaining starting from the DC supply voltage, a transistor and a transformer (more or less complex) that transfers the pulses to the user. The transformer is used: to elevate the voltage, when the switching has to feed the users that require more of the input voltage, or lower it, in the opposite case; to galvanically isolate the input power from the circuit in which the user is located. The galvanic isolation is not always required, so often the transformer serves only to change the desired voltage. The transistor works in on/off mode, then dissipates very little, because when it leads the lost power on it is equal to the product P=VCEsat x IC. The principle diagram is shown in Figure 6.1: the circuit used to generate rectangular pulses with which drive the transformer is an astable multivibrator based on the popular NE555, but instead of this can be any of a pulse generator also fed back to adjust the dutycycle the load conditions. The output of the integrated circuit drive a NPN transistor type BDW51A, which functions as a solid-state switch: in correspondence of the pulse goes into saturation state and let the primary winding of the transformer is crossed by the supply current; due to this condition, to the ends of the secondary is induced a new pulse, in the opposite direction, the amplitude of which is proportional to the turns ratio. At the breaks, the transistor back interdict and leaves isolated the primary of the transformer. Each pulse passes through the rectifier diode D2 and goes to charge the filter capacitor C4, to the heads of which is to find the DC output voltage. For this to work, the windings must be carried out in the same direction, but then on the other hand are connected to each other: the blacks dots in the proximity of the transformer indicate the start of each winding. If you miss a connection, the capacitor is not loaded, because D2 blocks the impulses, which would come with negative polarity; in fact, imagining watching the transformer as shown in the drawing, if the windings are made in the same relation to the voltage induced in the secondary has positive polarity down. Only by reversing the connection, the pulses become positive on the anode. The capacitor C3 is used to filter the power supply of NE555 from ripple that the absorption of the primary during current pulses causes to the positive line of Vin; instead, the diode D1 protects the transistor from overvoltage that the primary produces at each current break. This is because each winding inductance and the inductance has inertial character against the current: powered continuously, initially does not absorb anything, but is opposed to being crossed by the current and soon after begins to conduct and; when adapted to a certain current regime, try to keep it even if the circuit is interrupted. The inductance is like a mass: if a force is applied, initially it is hard to move ,

www.riparazione-notebook.net Figure 6.1 A simple DC/DC converter schematic diagram with transformer. 90

Figure 6.2 Waveforms (you can see in an oscilloscope) detected at primary (Vp) and secondary (Vs) of the transformer, and furterly at both ends of the filter capacitor C4.

but then picks up speed and, in the absence of friction, tends to flow without stopping and without requiring additional boost. This behaviour is explained by the Lenz’s law, according to which an electric winding subjected to a certain voltage, in the instant in which it is fed develops an induced voltage equal in value but opposite in the direction to that which generated it. In continuous voltage, the inductance allows the sliding of the current regime , which depends on the sum of the internal resistance of the voltage generator and that of copper which forms the thread with which it is built, only after a certain time interval determined by the total resistance and from the same inductance value. Therefore, the primary winding accumulates a certain energy and, removing current, it reacts by generating a reverse voltage of even very high value, which depends very much on the secondary absorption (higher is the latter, the lower the energy remained in the inductance relative to the primary, and vice versa), the reverse voltage will damage the base-collector junction of the transistor, and is therefore that connects the diode D1. It, when T1 leads is forbidden, because reverse-biased; at interdiction of the transistor, the reverse voltage generated across the primary sends the diode conduction, so that it will absorb the current and the residual energy. Switching on the power supply transformer you can make some considerations that apply to all its variants: in parallel to the primary winding is always a diode, dimensioned considering that the maximum current that must endure can be estimated at about 1/3 of that of the collector of the transistor responsible for switching on the primary; the diode must be chosen of the fast type, ie with a transition time from the conduction to

interdiction state (TRR) of less than 1/20 of the period of the rectangular voltage which drives the transistor and, however, that both the lowest possible; you can avoid using the diode transistor specific for the switching of inductive loads (for example, the BU508D) incorporating a diode connected between the emitter and collector, and that can then short circuit the reverse overvoltage produced by the transformer; the rectifier diode (D4 ) must be chosen with T RR less than 1/20 of the period of the rectangular voltage which drives the transistor and, however, that both the lowest possible; must endure an If (forward current) 20% higher than that from deliver to the user and a repetitive reverse voltage at least equal to the width of the pulses in the secondary, and this because of the peaks also occur at the interdiction of the transistor and these peaks are negative; the transistor must be fast enough, or have a switching time of less than 1/20 of the period of the rectangular signal that drive its base; otherwise continues to conduct even when it should not, and increases the power loss, which in it and in the diode rectifier are essentially linked to the working frequency; the transistor should be chosen with a V CEO of 20% greater than the supply voltage of the switching circuit (transistor/primary) and must withstand a continuous IC greater than the maximum current which is expected to give the transformer, the latter is determined as Iu=Vi x Ii/Vu. DC/DC push-pull stage The converter just described works by driving the transformer with unidirectional pulses, then the rectifier used which can not be of the single half-wave, the filter capacitor is therefore loaded only once during the period. To obtain a component which is better leveled is possible to make use of a circuit in which the primary of the transformer is fed during the whole period; thereby the rectifier can be of the double half-wave: more specifically, it uses the same configuration already view for the full-wave rectifier coupled to the transformer with center-tapped secondary. On this architecture, are two possible variants: the first (Figure 6.3) uses a single transformer primary driven with alternating voltage through the adoption of a bridge (bridge); the latter circuit is a four- transistor, two NPN and many PNP, mounted in a way that will lead, alternatively, the NPN and PNP of a side of the other. Because it functions properly, the bridge should be driven giving the transistor of each side of the same signal, in turn, one side always receives a control voltage in phase opposition with respect to that received from the opposite side. When the bases of T1 and T2 receive positive pulse leads the only T2 (T1 PNP to conduct needs and that its base is negative with respect to the emitter) at the same time, the bases of T3 and T4 are set to zero volts and goes to run T3 (T4 is an NPN and conducts only when the pulse arrives). In this condition the primary winding is traversed by a current that flows in from the extreme lowest to When the situation is reversed, the bases of T1 and T2 receive zero volts and the positive pulse of the T3/T4 and now leads T1 and T4, so the current flows into the emitter of the first, out of its collector, through the primary winding entering from the head up and out of the bottom one, then enters T4 escape from the emitter to the collector. Note that the

control voltages should have the same amplitude as that of power supply (+VIN ) otherwise the PNP transistors are always conducting. The bridge control circuit is often used in many DC/AC modules designated to control the backlight of the display of the notebook; see, for example, the schematic diagrams in Chapter 10. In the second version of the DC/DC converter with bidirectional control (Figure 6.4) is adopted a center tap primary winding powered from a stage named push-pull: the power is fed to the positive input line (+VIN ) and the ends are closed on the negative, one by one and alternately, by T1 and T2. This circuit also has it that the transistors are biased with two square wave voltages opposite in phase. The operation is as follows: when T1 receives the impulse goes into saturation, and in the upper section of the primary current flows coming from the positive supply; closes the current in the collector and from it, through the emitter. Simultaneously, the other section is isolated, because T2, receiving zero volts in the base, is interdicted. In the second half of the period the situation is reversed, and T1 base are placed to zero volts, then goes interdict and leaves isolated the top of the primary. T2, instead, let the current flows, since its base is now receiving the positive pulse, and its collector allows current to flow from the positive power in the lower section of the primary current from the collector emitter closes and then on the negative. Here, too, you can make some considerations: the first concerns the size of the primary, which, in the first case, must be calculated considering what you’re getting in one half of the secondary; for example, if the output voltage and therefore to half the secondary must be equal to the input supply (VIN), the primary must be composed by the same number of turns of the half secondary. Instead, in the case of the switching with a center tap primary, each half primary must be calculated on the basis of half secondary; therefore, wanting that the output voltage of the circuit is equal to that input, an half primary must have the same turns of the half secondary.

Figure 6.3 - DC/DC converter with bridge driver: this kind of stage allows to use a single primary transformer and to obtain equally an alterned voltage, it can be rectified by a double half-wave rectifi

The electric transformer Figure 6.4 Switching and output stage of a tipically DO/DO pushpull circuit: here, the transformer have a center tap primary winding.

At this point, to better understand the operation of the power supplies should spend a few paragraphs on the transformer: it is a particular static electric machine, which does not generate current but transfers an electric power between two circuits changing its parameters, ie current and voltage. The transformer is very useful in electronics: it is used to get the low voltage starting from the network to 220 Vac, but also to raise low voltage in order to drive sirens or get electric shock or ionize the air; also serves to transfer a signal between two circuits that must be kept isolated from each other and therefore also in telephony. The transformer works by exploiting the principle of electromagnetic induction, and is composed, in its basic form, by two windings of copper wire suitably isolated called primary and secondary (Figure 6.5). By standard, the primary is the one that receives the power supply and the secondary one in which the voltage is induced to reach the load. Usually the two windings are separated, ie they are electrically separate circuits (galvanically isolated), which shelters it from a lot of problems that would occur by taking power from the electricity grid and, in many situations, enables the operation of circuits that would otherwise not never would work . But there are special transformers, named autotransformers, in which the secondary winding is an extension of the primary or is an integral part of it. The windings of the transformer are made on a core of ferromagnetic material, that in the AC/DC power supplies, the large part of the inverter and switch

www.riparazione-notebook.net Graphic symbol of transformer (step-down on the left and step-up on the right). Primary is winding placed on Vi side, while secondary ar the one placed on Vu side. 94

ing to low-frequency (up to tenth of kHz) is a stack of laminations of silicon iron or simple grain oriented E+I or double C shaped. In some cases, especially for small transformers, for cores are used other shapes, like spool, 8 ecc. For the high frequency transformers, it uses cores compounds from a mixture of ferrite. The windings are made of a spool of insulating material. In power electronic devices for home and work, the transformer provides galvanic isolation of the electronics from the mains, which preserves from “electric shock” when you touch the wire feeder that would be in contact with the phase wire of the network. The transformers used in AC/DC adapters notebooks have always, for safety reasons, galvanically isolated; the DC/DC on their motherboards, however, can also make use of the auto-transformers, since all stages of the computer are referred to a common ground. Operation of the transformer The transformer is a component that works only if there is change in magnetic flux, which occurs only if the primary is powered by a variable current, whether pulsed or alternating. Moreover, the voltage induced in the secondary is in phase opposition with respect to that which feeds the primary: when these is positive, the other is negative and vice versa. The phase must be considered assuming wrap primary and secondary in the same direction; calling B the end of the primary winding and D that of the secondary, supplyng current is seen that the voltage VCD has polarity opposite to VAB ( Figure 6.6 ). If the two windings were made from the same number of turns, the following relationship applies: Vcd = -Vab A characteristic parameter of the transformer is the transformation ratio and represents the ratio between the secondary voltage and that the primary (r=Vi/Vu). Is usually expressed as the ratio, then 1:1 is to indicate that the transformer presents to the secondary a voltage value equal to that which feeds the primary, while 1:10 means that the transformer is on the secondary elevator and

www.riparazione-notebook.net Secondary voltage of a transformer is always in opposite phase respect primary voltage. 95

gives a difference of potential 10 times greater than that which feeds the primary. Admitted not having any power loss, you can write that: Vi/Ii = Vu/Iu Vi and Vu are, respectively, the voltages across the primary and the secondary, while Ii and Iu, respectively, are the current that flows, respectively, in primary and secondary windings. Appears as the output current from the secondary is directly proportional to the ratio of transformation: Iu = r x Ii or, if you prefer: Iu = Vi x Ii/Vu Being (neglect power loss) the power available to the secondary of the transformer equal to that taken from the primary: the higher the voltage of the secondary, the smaller the output current, and vice versa.

Inductance charge DC/DC converter In addition to the transformer-based, switching converter exists in another version, whose principle of operation is based on the release of the energy stored by an inductor or, more exactly, a transistor feeding a coil, and then cuts off the current and let the energy stored in it spills over the load. The level of the output voltage is decided, not using the transformer but playing on the width or the pulse frequency with which it is loaded on the inductor and inductance value. The structure varies depending on the circuit layout of the transistor, which can work on common collector (Figure 6.8) or a common emitter (Figure 6.7). In the first case we speak of buck converter, while in the second of the boost converter; in the latter, the coil receives power from the collector each time the transistor is brought into saturation while in interdiction, the inductor attempts to maintain the conditions of the run and generates an overvoltage that force the flowing of the current in the transistor. In order for the base-collector junction is not damaged, in circuit is added the DC (clamping diode) diode, whose function is to lead current and let, when transistor is blocked, current flows from the head of the coil connected to the collector to the diode Ds (is a Schottky diode) and from the anode of the latter to the positive electrode of the capacitor, then, from the negative edge of this capacitor to anode of DC diode. When the transistor starts to conduct, provides a new current pulse to the coil L, which, in the subsequent pause, deliver its energy to the load and to the fil About the common collector layout, the operation is as follows: when the base of BJT is polarized forward, the emitter current flowing in the inductor L and from it in the capacitor; at the interdiction of the transistor, the coil tries to maintain the same current but, since it can not pass into the emitter, find an alternative route through the capacitor and then in the Schottky diode Ds. In the next conduction phase of the transistor, inductor

receives a new amount of energy, which then download, through Ds, in the capacitor in the following break of interdiction. Figure 6.7

DC/DC with voltage feedback The inductance charge based DC/DC converter can be provided of a feedback system, so as to stabilize the output voltage to a predetermined value; this is achieved mainly with two adjustment techniques: varying the frequency of the rectangular signal which drives the switching transistor, in order to vary the duration of the charging pulses of the filter capacitor, or keeping constant the frequency and playing on the duty-cycle, then to the transferred energy. An example of a regulated inductance charge DC/DC circuit based on variable frequency is shown in Figure 6.9; the Figure 6.10 shows, instead, a DC/DC regulated winding inductance with variation of the PWM. Transformer-based DC/DC PWM-regulated The same techniques of modulation of the working frequency or the duty-cycle rectangular wave at a constant frequency can also be applied to the DC/DC circuit based on transformer, in which case, the voltage which gives an indication on the level of Vu is obtained by a divider resistive in the DC / DC where it is not required galvanic isolation between the control stage and output , or with a second transformer or a photocoupler, when, instead, the control circuit and the load should not have connections in common. In practice it is only used in the configuration variable duty-cycle, the variable frequency is inconvenient because, growing along with the frequency of input current, the higher the load, the higher the frequency,

Figure 6.8

Figure 6.9 Inductance charge DC/DC with adjust network and working at variable frequency.

while undermining the transistor and diode rectifiers and clamping. Furthermore, since the losses are proportional to the frequency, the yield decreases with increasing load, more than what happens in the DC/DC that are working at fixed frequency. These considerations apply to all switching: transformer-based and inductance charge type. Therefore, we examine only the circuit variable duty-cycle, which can have the structure shown in Figure 6.11. The operation of the driver stage is similar to that of the variable duty-cycle inductance charge converter: the comparator compares the triangular voltage produced by the generator with the continuous component reported from the exit, by means of the resistive divider; the latter serves for adapt the level of the component applied to the inverting input of the comparator to the width of the triangular. The sizing is conducted, making sure that the triangular wave has an amplitude less than or equal to that of the voltage drop across RB. The frequency can be decided according to the characteristics of the transformer and the directions given on the subject of DC/DC transformer is not regulated. As usual, the secondary winding of the transformer is connected to the opposite. To achieve a double half-wave circuit, an operational amplifier must be mounted to the comparator, which

inverts the signal to send to the second transistor of the push-pull, or a logic that creates the necessary signals to the bridge stage.

www.riparazione-notebook.net Figure 6.10 Inductance charge DC/DC working at variable dutycycle. 98

Figure 6.11 Transformerbased DC/DC converter, provided of a feedback circuit and working at fixed frequency and variable duty-cycle.

Compared to the inductance charge converter DC/DC, the transformer-based DC/DC (regulated or not) does not suffer of the power losses in the inductor, but must deal with the performance of the processor, which means that, at the end, with the transformer (because of losses in the core) you lose something more than what is lost in a inductance charge circuit made with an inductance that have high quality factor. For the rest, there are the usual losses in the diodes and transistors. Thus, the transformer-based DC/DC converter has an upper power loss than the inductance charge, but it is safest to use it (in the version with input and output referenced to a single mass too) when you need a negative output voltage respect to input voltage, or it need more protection of the user obtained via ground separation and galvanic insulation. In fact, if in the inductance charge circuit a transistor is broken (short-circuited in buck layout or interrupted in boost configuration) the output receives a voltage close to that of input; with the transformer, instead, the output goes to zero. DC/DC galvanically isolated When a transformer-based configuration is used to power a circuit that is to be electrically decoupled from the starting voltage, the feedback signal can not be brought to the control circuit refers to the common ground (negative power supply); it must be done to get through a second transformer connected with

www.riparazione-notebook.net DC/DC converter with variable duty-cycle carried by a feedback network based on a electrical transformer. 99

Figure 6.13 DC/DC with feedback carried via a galvanic isolated network: in this case, feedback signal is obtained from an optocoupler.

the primary to the secondary of the main one (Figure 6.12). The transformation ratio of the transformer must be chosen according to the width of the output component. In the diagram, the voltage obtained with the auxiliary transformer, rectified and smoothed, is applied to a potentiometer: what the purpose of allowing accurate adjustment of the DC component given to the comparator. Note that more closely resembles the cursor of the potentiometer to the mass, the more Vu voltage increase, because it decreases the feedback voltage and the comparator gives the base of the transistor pulse wider, ie T leads to a greater portion of the period. Vice versa, approaching the cursor to the cathode of the Ds3, the amplitude of feedback component increase, the triangular wave oscillator exceeds that of the pin 2 of the operational amplifier to a lower portion of the period T and leads to less time, reducing the output voltage. In alternative to the transformer, can be adopted with the feedback optocoupler (optocoupler) type 4N25, 4N35, CNY75 and similar, according to the scheme of Figure 6.13. The LED (light emitting diode is connected to the anode and the cathode to pin 1 to 2) of the optocoupler is polarized through R4 from the power supply output voltage, so that enter into conduction the phototransistor (with the collector connected to pin 5 and emitter to 4), which determines a potential difference across the bipole R5/Dc, proportional to Vu. The usual potentiometer (functioning as already described for the circuit feed- through transformer) allows accurate adjustment of the output voltage.

Converter based on Integrated Circuits In the market there are numerous chips that allow you to make excellent DC/DC, either inductance charge type or transformer type.

A good example, among the most used in the production of DC/DC converter, in power supplies of desktop PCs, and in those of notebooks, is the SG3525, built by numerous manufacturer such as ST, Exar, Signetics. It is a complete switching regulator containing one stage generator of the reference voltage (5.1V), an error amplifier, a saw-tooth waveform generator and a current protection, in addition to a double output stage functioning in counterphase. The SG3525 is therefore designed to drive a transformer stage with two transistors in push-pull, but nothing prevents you to use it with only one exit, driving a single transistor that supplies power to a transformer or inductor. Using both outputs, when a positive pulse gives the other occurs at zero volts . The internal oscillator can work between 100 Hz and 500 kHz; requires, for the operation, a capacitor connected between pins 5 and 12, and a resistor connected between pins 6 and 12. The supply voltage of the component must be between 8 and 35 volts. The circuit of Figure 6.14 is a DC/DC that, depending on how one chooses the transformer, can be elevator or reducer, with the current components is expected to be 24/12 V, from well 10 A output. The fuse F1 to be calculated for the current absorbed by the transformer primary and the same applies to the filter coil L1 (inserted in a pi-greek network used to suppress noise arising from the switching of the MOSFET). The SG3525 here works at a frequency of 50 kHz.

Issues of the filter capacitors The capacitors, especially those of large capacity, are suffering from a parasitic series resistance (E.S.R.) that is felt especially in electrolytic processes, and they also have a conductive component, resulting from the terminals. If in the linear power supplies these components are not perceived, in switching, especially those that operate above 20 kHz, can give many problems. In particular the resistance, which introduces a time constant capable of delaying the charge and thus limit the leveling of the voltage delivered by the converter. But not only determines the resistance power dissipation, the capacitor should not present, it causes overheating and degradation in the long run, the dielectric that separates the plates, resulting in loss of capacity. Moreover, the dissipation on the ESR increases losses, by subtracting the output power and thus reducing

www.riparazione-notebook.net DC/DC converter transformer-based build around an SG3525 integrated circuit. 101

the conversion efficiency. For these reasons, when designing a switching who works at frequencies greater than 20 kHz is preferable to choose low ESR capacitor, which are made explicitly for use in switching devices. The capacitors in polyester, mylar and polypropylene, but also the multilayer ceramic, usually tolerate well the high frequencies and have low parasitic inductance and for this reason, when it is necessary to filter the input power of the DC/DC to turn off the pulses caused by transistor switching on the inductance or on the primary windings of the transformers, it is convenient to put one or more in parallel to the electrolyte used to filter the power line input. One final note about the sizing of the electrolytic filter in the converter transformer: they are much smaller than those used in power supplies, as the frequency with which they are charged is much higher. Without making too many calculations imply that the graphical reconstruction of the cycles of charge and discharge, it can be said that, for a duty cycle of 50 % can be considered 1.000µ F/A from 500 to 5,000 Hz, 500 µF/A from 5 to 20 kHz, 200 µF/A from 20 to 50 kHz, 100 µF/A from 50 to 200 kHz.

CHAPTER 7 NOTEBOOK STRUCTURE In order to repair a laptop or at least hypothesize what failure may have, you have to know the basic structure of this. The purpose of this chapter is to give an overview on the gross composition of a notebook, it being understood that each PC will then have something more or less and that over time may be added to the basic structure of the new elements introduced by technological innovation. In general, a modern laptop (meaning “modern” that was built for ten years) is composed of the following parts: a microprocessor or CPU; a program memory (EEPROM or Flash EPROM); one or more memories RAM; a bus interface; chipset that controls the functions of the bus and power supply; a series of peripheral I/O overlooking the bus; one or more controllers for the disk drives; a graphics adapter (graphics card) with any memories; an audio adapter; a network adapter; any wireless interfaces; any modem; one or more internal power supplies; an external AC/DC power supply; a display;

a keyboard;www.riparazione-notebook.net105 a pointing device (mouse or touch-pad); one or more mass storage devices (hard drives and card readers); a floppy-disk; a reader/writer of optical discs; one or more cooling fans; an accumulator (battery). Below will be analyzed one by one in detail, it being understood that they (except disk drives, fans, keyboard and pointing device) are placed, depending on the type of computer, of: a motherboard; one or more daughter boards . Display and power supply was discussed in detail in Chapters 5 and 6, so we will not dwell on the subject. Motherboard is the name that, rather inappropriately, is assigned to the main board of the notebook, which always hosts the CPU and the RAM sockets, plus the BIOS non volatile memory; often the same motherboard shows the interface connectors (ports I/O) and the external monitor, in addition to audio and power. The term derives from the motherboard desktop computers, where there is actually a main board equipped with standard connectors which are inserted in the various cards (audio, video, I/O units, etc.). The motherboard is also called mainboard. For daughter cards are small circuit boards that contain components or connectors, or peripheral I/O and, at times, the separate video card. It should howev

106 www.riparazione-notebook.netFigure 7.1 - Typical block diagram of a notebook PC.

er be noted that there is often only in the notebook motherboard. The disk drives are external to the motherboard and are supported by the body of the computer, the latter is formed by a lower half and an upper one. The display is also hosted in a shell formed from two halves and is hinged on the base.

CPU Also improperly called “microprocessor”, is an integrated circuit that is at the heart of the notebook, since that makes everything work because it provides data processing. To understand how this works we must first know the ALU (Arithmetic Logic Unit): this is a binary circuit capable of performing operations of addition, subtraction, multiplication, decrease and increase of compound words from a number of bit or compare two words. The ALU then the calculation unit of the CPU and to accomplish a given task makes use of external circuitry such as a series of records where to put the data for the provisional calculations and results and records (memories ) are primarily used to manage complex operations such as division between byte or binary words, which

Figure 7.2 - Parts of a mainboard of notebook, seen from upper (on the left) and lower (center); tabel on the right details each part on the board.

can not be accomplished directly, but must be carried out in multiple steps. The ALU is defined by the number of bits that can draw together, or by the size of the words on which it may carry out operations; may be 4, 8 or more bits. The CPU (Central Processing Unit) is an integrated circuit that incorporates the ALU, registers and amount of RAM needed to perform mathematical operations and even has the control unit, a block that deals with the ALU to work, with which it interacts by ordering them to perform certain operations, and interrogating the status of those under development. The control unit is part of the logic for status signals, also known as bit flag: the flags are used to communicate the status of implementation of operations or the sign of the result of an operation performed by the ALU; are useful, for example, to perform operations such as division, that the ALU alone

could not do. In the CPU, ALU performs calculations according to the instructions, which are binary words that a decoder in the control unit converts operations, and every time the unit is receiving an instruction, work cycles to complete the required task. The time it takes to complete an instruction is called instruction cycle and is defined in the specifications of the CPUs and microcontrollers and microprocessors: the more it is reduced, the device is much more handsome. The instructions are read by a special non-volatile memory (program memory or program memory) outside the reading of which is punctuated by the Program Counter, the latter is a counter that dictates the order of execution, directing , one location at a time, access to a nonvolatile memory in binary form, which is the language directly interpretable by the control unit (machine language). One of the registers in the CPU is the accumulator, which is the register taht contains one of the operands before the operation, and the result of operation after the operation; the control unit includes a counter and a decoder. Externally, the CPU requests a memory that contains the program, the clock signal which marks the operations and interface logic, the latter serves to direct the external RAM, the devices which are directed data, but also to make travel the data both to the devices, both by them to the CPU. The set of address lines is the Address Bus or Bus addresses, one of the data lines, the Data Bus or Bus Data. Note that while the first sends out signals only, the second is bi-directional, because he sees the data go CPU on the outside and vice versa. The data come from the CPU, for example, when it needs to write in a memory or give information to a

www.riparazione-notebook.net A microprocessor used in notebook computers: is an AMD Sempron Mobile CPU, encapsulated in a socket 754 case. 108

D/A converter that must reconstruct an analog signal; entering the CPU when, instead, it is reading from an external memory or acquiring data sampled by an A/D converter. Note that the amplitude of the data bus depends on the size of the binary words that the CPU can process; the larger is, more powerful is the device for the same instruction cycle. The size of the bus defines the architecture of the CPU, which is 8 bits if the data bus is 8 bits, 16 bits if the data bus is 16-bit and so forth. To assess what has been the progress in the field, know that the first CPUs were based on only 4-bit ALU, while modern ones, now used in the simple IBMcompatible personal computer, they are also 64-bit. The CPU can exist as a stand-alone integrated circuit (containing an ALU and control unit plus a little of external registers) but in the last twenty years, thanks to the possibility of achieving an acceptable cost integrated LSI and VLSI, it is preferred to shoot in a single chip the power set of a CPU. Thus was born the microprocessor. Microprocessors are the old 8088, 8086, 80286, 80386, 80486, and the latest Pentium, Pentium II, III and 4, AMD K6, Athlon, Sempron, Turion, Opteron etc. Typically, in a microprocessor are integrated a CPU, the I/O registers, a RAM and a register stack. The processing capacity of the data depends on the features of a microprocessor CPU which contains and, more precisely, by the number of bits of ALU and the frequency of the clock signal, but also by the number of executable instructions per clock cycle. Not always microprocessors operate with bytes, but newer ones treat word of 16, 32 or 64 bits, so in the technical specifications are defined both the data bus, and working memory, in word. Moreover, what makes the difference is also the size of the instructions, which may be 4, 8 bits, but also more: for example the units operate with Microchip RISC instructions in PICBasic formed by word of 14 bits. The registers of I/O processors are the Input and Output (hence the term I/O) which lets you copy out the data bus, bi-directional drivers are normally able to change course of the data resulting from a calculation and send them out to the data bus, or to direct incoming data on the bus to the internal registers of the CPU, because that provide to accomplish the necessary tasks. Typically, the input and output registers have many lines as there are bits of the data bus and of an address -bus , although there are exceptions in which, in order to limit the external dimensions of the chip, and then the number of pins, a portion of a bus becomes, if necessary, part of another. An example is a microprocessor which has 16 bit data bus and 16-bit address, but does not have enough pins; in this case it can be done so that 8 bits of an address bus now become addresses, time data. The thing is realized using the latch multiple (eg TTL 74373 and 74374) that are groups of flip- flop (usually 8 at a time, to adapt to the data bus of the microprocessor to 8 bit) connected to the latch: each of them, when it receives a pulse on the line of activation (strobe) loads the input data and takes them out, keeping them even if the inputs are changed. The common 8-bit are made to pass by a latch, the outputs of which are facing the address bus; a bidirectional linedriver faces, instead, the bits on the data bus. When should target a device, the micro

(which has a dedicated line for the purpose) gives the strobe signal to latch and makes load addresses, while holding off the line driver that overlooks the corresponding portion of the data bus; when have to read or send data, the microprocessor releases the strobe and lock the latch with outputs in the position previously adopted, while controlling the linedriver in order to manage the flow of data. The mixed use of lines of data and addresses has been done in different microprocessors: such as Intel 8088, 16-bit internal and external 8+8, but also in devices used in the PC of fifteen years ago, such as Intel 80386-SX, which were distinguished from the DX to have an internal data bus 32-bit and 16-bit external. The same was true for 80486SLC, versions of the 80486 -SX mounted in a case compatible with the 80386-SX. Generally, a microprocessor has the following inputs and outputs: data bus; address bus; control of read and write (R/W); strobe of any shared bus. The read/write control line is a line that is used to tell the devices connected to the bus if the data on the data bus during the current operation are sent by the microprocessor or the microprocessor must read them in the case of the memories controls the read/write and allows you to read or memorize. The same line controls the line-driver input to switch the direction of the data bus.

110 www.riparazione-notebook.netFigure 7.4 - Schematic dia gram of the microprocessor’s ALU.

Interrupts and cache memory A special feature of CPU and microprocessors is the ability to temporarily stop the program running in order to perform other tasks. To receive the interrupt requests, the microprocessor has one or more inputs said interrupt, which act in various manners; if interrupts are more than one, may be provided a priority of one over the others (so if they come closer together, the CPU knows which already has to consider first ) or the architecture provides the ability to disguise some, namely to decide, by the running program, which must be ignored when certain working conditions. Sometimes it makes use of a specific interrupt handler. To always find the point where it left off at the time of the CPU contains a register to stack (the already mentioned stack register stack) where each time they are placed one upon the guidelines of the program counter as hand the corresponding instructions are executed; stacker is like a stack of documents that an employee, after completing, puts one over the other. If someone interrupts the work of the employee to ask him to make another one, on his return to the table takes up the row and see what was the last document compiled. So does the stacker of the CPU. Interrupts are also managed by special chip outside the CPU. To speed up the execution of the calculations, the microprocessor often uses an additional RAM memory said Cache, or (Cache Memory) where positioned momentarily instructions executed recently, which has chronologically; in this way, when it should perform a certain calculation already there ready and education saves time, since otherwise it should stop playing and pick her up in the program memory. The cache can be internal to the microprocessor, and in this case is called level 1 cache, or external (in which case it is called level 2 cache); many microprocessors require the use of both internal cache (ie integrated in the chip) and external (mounted on the board where the component works). Intel microprocessors begin to use internal cache with the family of 80486 DX486, which had some kB of 1st level cache; the 80486-SX had not been provided and required apart, mounted on card that host microprocessor. The same applies to the i586 family: the Pentium were aboard the cache, while the Celeron had none and required special mainboard with cache activated using the setup. A separate discussion were the Pentium II, Pentium MMX that were essentially mounted on a base which also contained two caches Level 2, for a total of 512 kB; in which case the level 1 cache was always that of the common Pentium processor. In the Pentium II used in notebook, cache was always on the motherboard. The mainboard of your desktop PCs created to support Celeron or Duron, since the latter have not its own second level cache, had an on-board cache; the problem of this is that while some may identify themselves and disable the processor cache on-board in the case of a Pentium II or III or Athlon, in other activation or deactivation was to be accomplished by the BIOS screens, otherwise they created memory conflicts able to stop the computer activity without cache was deactivated. Almost always, the CPU of the notebook is mounted on a ZIF (Zero Insertion Force) in which it occurs effortlessly, thanks to the fact that it provides a release mechanism to get

to the bottom of the integrated circuit pin and then tighten them through a lever (for example, socket 370) or a screw closure. Math coprocessor To streamline the workload of the CPU , the Intel processors starting from 80486 was introduced to the math coprocessor, which is a computing unit which operates in parallel with the CPU itself and which deals with mathematical calculations; in the series i486, the math coprocessor that powered the 80486 -DX , while the SX , cheaper, had no coprocessor, but the SX processorbased computers could mount it as additional element on a plinth separately (the coprocessor was 80487). Floating point unit Also called FPU, is a kind of ALU that will take care of the floating point calculation for the execution of instructions that require it; operates in parallel with the CPU and is integrated in the microprocessor. In the series Intel, is present from 80386, and the same goes for AMD CPU which 80386, 80486, 80586, K6 etc. Just the K6 seems to have had, in its early versions, problems in the floating point calculations unit. Program memory It is a permanent solid state memory wher is loaded the basic program which allows the CPU to work and load the operating system (eg Windows, Linux, etc.). This program is the BIOS (Basic Instruction Operating System) and in addition to start the computer performs the basic functions and allows you to boot the system. It consists of basic instructions to initialize devices and communication bus, then to access mass storage devices and boot from them (bootstrap ) the operating system. This is an advanced software that allows full use of the computer resources and provides the user with an operating environment where to run the utilities and applications (such as Microsoft Office, Open Office, Adobe Photoshop, AutoCAD, etc.). One can understand this program hierarchy considering the instructions executed by microprocessors are actually binary words whose function is simply to present a logical combination of input ports constituting the ALU so that the data to be processed (operands) subjected to a specific logic operation. The only instructions directly understood by microprocessors and microcontrollers are those in machine language, which is in binary format. Given that each of these corresponds to the execution of an elementary operation, it is evident that to write a program also should be relatively simple fill hundreds of rows and impart many instructions. To simplify the compilation of programs were born level languages, in which instructions is actually the set of most machine language instructions, the simplest of them is the mnemonic code. To make it clear to the microprocessor mnemonics as instructions written in the languages most advanced, you need a compiler, interpreter program that serves as mnemonics and turns in the group corresponding instruction: an example is the assembler (assembler program). The mnemonic language is a cross between a high-level language and machine language, since it is strongly bound to the physical structure of the corresponding CPU. The real evolved languages are the various Basic, unlike the mnemonic code, partially transcend the physical structure of the microprocessor and are therefore suitable for programming various types of CPU. Languages are still the most evolved Cobol, Fortran and C, in its various versions, which have been written but not for use with microprocessors alone but with cards in which architecture microprocessors are provided and a number of I/O

peripheral and memory; these languages almost completely disregard the type of microprocessor but apply enough unconditionally subject to certain architectures, such as those of the Personal Computer. So enough for him that the computer has a CPU with certain characteristics and then the interpreter does the rest. Further evolution is represented by object-oriented programs (Object Oriented Languages), and however by state Visual Basic, Visual C, Delphi, not made to handle the CPU itself but an entire computer, where specific software managing the execution by the microprocessor. The operating systems are written in easily understood (through interpreter) from microprocessors: for example, Microsoft Windows was written in C instead of the programs that run on Windows, are written in languages which are not intended to command the microprocessor, but that activate only certain features of the operating system. Basic programs, or the BIOS, serve instead to allow operating systems to use the computer’s CPU, among the functions of the BIOS is setup, which is a panel setting your computer’s hardware and interaction with the operating system. The memory containing the BIOS is typically an EEPROM or a Flash EPROM, which is faster. If there is a fault in the memory, the computer can not boot.

RAM Memory They are the work memory of the computer, ie those for which the CPU uses to process the data, or in order to pass those to be processed and temporarily store the partial results or maintain information necessary for the execution of a program or video display. The RAM is divided into two basic categories: static (SRAM) and dynamic (DRAM). The first, once acquired data (after their fundamental cell has switched the state imposed) remain as they are, as to the dynamic RAM, need a refresh, ie a continuous updating of the written data that would otherwise be lost. The cell of static RAM is based on a transistor BJT or MOS N-channel, but also on a structure CMOS (complementary two MOSFETs); instead that of a dynamic RAM is a capacitor, that is the section gate-channel (substrate ) of a N-MOS structure. The substantial differences between the two are in power consumption in the circuit complexity and the speed of access: the static memory cell dissipate more power because it consists of several active elements and takes longer to read than that required by the dynamics, on the other hand, is less expensive because its overall structure is simplified by the circuit refresh. Instead, the dynamic RAM has smaller cells and requires less power , since a given store is in a structure that is as a capacitor; however, are usually more complex, because they require refresh circuit which serves to periodically renew the charge in cells at high level (the refresh is performed simultaneously on all the cells), the data access is more rapid than in the dynamic RAM. Regarding access to the data, any memory has a number of bits allocated to addressing and one representing the location of the data to be written or read, a RAM (but this also applies to PROM , EEPROM , etc). Has therefore a data bus (set of lines intended for the same purpose) and an address bus, the first groups the lines on which the data travels and for modern memories has eight wires, while the second brings together the lines used to define, in binary format, from time once in the address where you can read or write. The address bus counts how many lines they serve to compose, in binary forThe address bus

counts how many lines they serve to compose, in binary for bit data bus, and then by 8 Kbytes, has 16 lines, because 2 to 16 is 65,536 , ie 64 kbit. To access the cells of the matrix starting from the address bus using a decoder (see later in this chapter), which, for each binary value set to its inputs (the address lines) comprises a logic that corresponds to a pair row-column. In addition to the lines to direct the location in which to operate and those containing the data to be written or on which you are receiving the read data, a RAM has the following contacts: R/W (Read/Write) is used to communicate to the memory if you want to write or read, the lines can be two distinct, but usually it is one and the action to take is to be forwarded (by the microprocessor or microcontroller) with a logical level; E (Enable) or CE (Chip Enable) enables the operation of the chip and is useful when building a memory bank with more chips when, having all the same RAM data bus and the address bus, it must be from time to time turn on the receiving of the data or the one in which reading, otherwise you read or write simultaneously in all, with the obvious consequences, sometimes called CS (Chip Whenever you have to write to a memory location (one location is a whole byte, then eight cells), the device that uses RAM, sets on the address-bus the address of the desired location, then commands the W/R line get the operation to perform, and then turn on the Enable; done that, if it is to write sends data on the bus, while if it is to read the contents of the location, the active W/R button in the operation of read. Currently you build RAM organized in bytes, then each address concerns a group of eight memory cells read or written simultaneously; capacities are of the order of a few MB. Typically the abbreviations of the memories are based on the total capacity, which means in cells, or in bits: for example, the 62256 is a 256 kbit RAM, but, being structured in byte (8 bits) is a 16 K x 8 bit, or a 16 Kbytes. The RAM used in personal computers and then built into notebooks for about fifteen years now are the DIMM ( Dual In- line Memory Module) and SDRAM; these two terms defined essentially two physical sizes. In turn, the DIMMs were divided into: FPM (Fast Page Mode); were the first not single-chip memories; EDO (Extended Data Output) have represented the evolution of the classic RAM and are no longer in use; they are static memories; The Fast Page were dynamic RAM organized 8-bit, whose speed was defined by the times on the single chip times (identified by reading the digit to the right of the hyphen after the abbreviation) ranging from 60 to 120 nanoseconds, but typically it was chip 8-bit data bus connected with the 4-bit parallel or connected in series-parallel, such as the 44C256 (256 kword) or 44C1000 (1 Mword) with eight chip of which were realized DIMM respectively by 1 and 4 Mbytes. The chips were used stacked in pairs because they were organized in 4 bits, so two were one byte; this explain reason why eight memories 256 kword forms 1 MB, while 8 memories 1 Mword forms 4 MB. The Fast Page were 4-bit, while the new born EDO were built with organization of the data bus 16-bit with Fast Page, a complete bank for 16-bit processors (80286 and 80386SX, characterized , the latter by a data bus 32 bit internal but external to 16) formed with 2 sticks , while processors with 32-bit data bus ( 80386DX , 80486 ) called for a bank 4 memories .

With EDO (adopted by the advent of the last 80486, as well as the Pentium, AMD K-5 and K-6) a bank was formed with only two sticks. All RAM for Personal Computers are composed of printed circuit boards (sticks) on which are mounted from 2 to 18 chip RAM memory, type parallel access; each circuit has, on one long side, of tin-plated or gold-plated contacts that bring direct power supply to the chip, the address lines and those of the data, in addition to control signals. In Fast Page there were 30 contacts, while the EDO, designed to work with 16-bit bus, they were 64 pads. In notebooks, at the time of the Fast Page RAM memories were not standard and each manufacturer provides built to specifications for its portable, which is why it was unthinkable to swap between PC of different brands, but also in the same house . With the advent of EDO, in the world of notebooks was attempted before standardization, realizing the size 64 contacts. EDO are to follow these memories, which are also organized in sticks: SDRAM: RAM are the dynamics used until a few years ago in personal computers (series until the first generation of Pentium IV and AMD Athlon XP); DDR (or DDRAM), it is of SDRAM in which the access time is halved, thanks to the fact that the read cycle occurs at twice the speed of the SDRAM; RIMM (or RAM -Bus) RAM are reserved for certain server, now abandoned and not used in notebooks. All these types of “modern” are characterized, in addition to the capacity and access speed is not more than (as was the case for Fast Page and EDO) but the bus of the computer with which they can operate. In addition, on a printed circuit board have an EEPROM where data is stored from the computer to identify them correctly. In addition, it is already 32-bit memories, so CPU including Intel Pentium, Pentium II, Pentium III and Pentium IV, and Cyrix/IBM 6x86, AMD Athlon, Duron, Athlon XP, Sempron, Athlon 64 and so on. To form a memory bank just one of them. The 168-pin SDRAM memory (84 for each face of the printed matter that creates) and speeds of 66 , 100 and 133 MHz, used with processors having the bus 66, 100 or 133 MHz; the speed of the RAM can also be submultiple of that processor’s bus, so it was possible to use SDRAM with 100 MHz with CPU have bus 200 MHz, or 133 MHz with 266 MHz bus CPU, such as the Pentium IV from 1,4 to 2 GHz. SDRAM were made in two versions distinct from the supply voltage: 3.3 V to 5 V; to avoid to install one in the place of the other (use SDRAM 3.3 V to 5 V in a circuit harmed by it…) the two have the reference mark on the printed circuit positioned differently. As for DDR, they are actually memories such as SDRAM, however organized and managed so that it can be read simultaneously on the two sides, which doubles the speed of data access; this means that using chip at 133 MHz, in reality the speed is 266 MHz.

www.riparazione-notebook.netOn the left, a DDR type RAM designed for desktop PCs (single side type, 4 chip, no parity); on the right, a DDR RAM for notebooks with 4 chip per side. 116

DDR 184 count contacts, equally divided on both sides of the printed matter (92 per side). The DDR have been developed for working speeds of 266, 333 and 400 MHz versions exist today called fast DDR2 and DDR3 memory, capable of working with microprocessors whose bas is at 533, 566, 667, 800 MHz and even beyond 1 GHz. The DDR2 and 3 are not compatible with the common DDR, as also change the operating voltages. In order to avoid that it can be fitted in place of each other, the reference mark is positioned differently. As for RIMM, only work with their dedicated bus and recognize because they have the reference mark at the center, they have very high working speed, ranging from 400 MHz up. In any PC, RAM is managed by a dedicated chip (DMA) that acts as a mediator between the CPU and memory, for some time, it is integrated into the chipset (MCH=Memory Controller Hub). The choice of RAM to be mounted in a Personal Computer memory as initial or for an upgrade, must comply with certain parameters: first, the memories must be of the same type and the same speed (or access time); also, when to form a bank it takes more slats, the RAM used must be identical, otherwise there may be problems such as slowing or blocking of computer operations. In desktop PCs, the RAM controller can support particular configurations of memory as the Dual Channel: this is reserved for DDR and DDR allows you to use two at a time to increase performance in terms of processing speed; the dual-channel configuration requires that the memories of each bank are equal between them. To indicate to the technician where to mount the same memories, sockets typically have different colors, staggered positions or reference tags. The RAM, from the old DDR Fast Page to today, can be either a single or double-sided, meaning that it can have the chips arranged on one side only or on both; making the choice is necessary to verify that the computer where you intend to mount brackets reading the desired RAM, because not all PC correctly read the memoirs double-sided: some read half of the actual capacity (one side only ) and others are blocked completely or work more slowly). RAM parity To check the correct writing of data in memories, given their complexity and the possibility that some cell functions not correctly, it was expected the socalled “parity check”; in other words, the memory controller when he writes a byte or a word makes the binary sum of the individual bits and then stores it in a cell for each word or byte parity bit. This bit is 0 if the sum of the word or byte is even (even parity) or 1 if the above sum is odd (odd parity). When data is read, the memory controller is to read every word or byte, is the sum and compares the result with the corresponding parity bit: if the value is consistent all is well, while in case of inconsistency (sum equal but odd parity) warns the CPU and the computer reports parity error. This control is usually carried out during the Memory Test, a process initiated by the basic program of the moth

Figure 7.6 Block diagram of EEPROM an EPROM: address linea are 20, that is how many it needs to address a 1 Mbit memory.

erboard (BIOS) at boot parity error stops the execution of the instructions and prevents the operating system from starting. However, this speech is a prerequisite to the fact that the parity check can be performed in the slats of memory or from a chip on the motherboard, usually contained in the chipset; in the first case the control is faster (because each memory stick executes it individually and communicates the response to the memory manager), however, requires a further memory chip dedicated. Instead, if the check is done on the motherboard, dedicated chip is on the latter. Therefore, the sticks of RAM with parity check have 9 or 18 chips (respectively for configurations 8-chip single-sided or 16 double-sided ) or 3 or 6 (if there are two or 4 chips, respectively, single and double sided). The sticks with 2, 4 , 8 or 16 chips are not equal and suitable for mainboard capable of carrying out its own parity checking. The memory chip in more serves to store the parity bit of all the word or byte of others.

Interface bus Your computer’s CPU does not directly manage the devices, but you interface with them via a bus, which is a set of links that are used to send and receive data to and from a variety of devices such as the sound card, the video etc. . The purpose of the bus is, therefore, unify the communication lines between the CPU and all the units that it must communicate with units that include hard drives, video card and the audio, communication ports and the pointing device and, in laptops, PCMCIA or CardBus card. The first bus used in personal computers was the ISA (8 or 16 bit) then it was followed by the VESA Local Bus, which is implemented but only to speed the flow of data on the video card and, subsequently, hard disks, because, already with the advent of i486 was felt the limit of the ISA, which formed a “bottleneck” that choked the flow of data to and from the CPU, certainly faster than But the VESA that was not a simple extension of the ISA and was added to it, was therefore introduced the PCI, however, also used in notebooks up to Pentium 233 MMX or AMD K6-2. The PCI bus is a completely different, 32-bit and therefore able to channel a greater

amount of data per unit time, due to its speed that could reach 66 MHz (against the 33 of the VESA) . But it is the intention of the producers and especially Microsoft, dominating the field of operating systems, was to transform the PC from a substitute for the typewriter to a real multimedia computer; because on the one hand those who were increasingly bought a PC to play and on the other there was the research by graphics professionals to find an alternative to expensive Mac, however best of PC, especially in the operating system used (MacOS). Needed to be accelerated audio and video data streams, but especially the latter, which is why it was introduced around 1997 AGP, a private bus to the video card, which has already taken hold in the notebook for over a decade. The AGP was produced in several versions: single speed initially and then accelerated with acceleration coefficient of 2x, 4x , 8x , 16x. The mainboard of the desktop computer there was only one AGP slot, which used the interrupt reserved for the video card on the first PCI slot, so that it was not normally possible to connect two video cards unless you move to a different slot from the PCI first. The innovative feature AGP compared to PCI is that it faces directly on the data bus of the processor and does not change from other chips. The last bus in order of time is the PCI Express, which is basically a remake of AGP, just a little speeded up, even the PCI Express exists in different speeds, up to 16x.

Chipset Under this term pass multifunction integrated circuits that substantially govern the activity of the computer, and group together constitute almost all of the logic and that have evolved over time as each set was designed for a specific CPU. Until a few years ago, it was common practice to equip the mainboard of the desktop and laptop computer with a set of at least two chips, called Northbridge and Southbridge, and the first (also named MCH or Memory Controller Hub ) will interface directly with the CPU bus and the AGP or PCI Express, or with expansion slots and audio devices and mass storage , as well as memory. The Southbridge deals instead of communication devices and other interfaces which require a lower flow speed data interchange: eg ISA and PCI bus. The function of Northbridge and Southbridge includes imagining the computer is structured as shown in Figure 7.7: in practice the Nortbridge communicates directly with the processor, while the Southbridge interfaces with peripheral devices. In architectures with Northbridge and Southbridge distinct, the Northbridge connects the CPU to the RAM, the PCI bus, the 2nd level cache and the video bus (AGP , PCI Express, etc.). Communicates with the CPU via the Front Side Bus (FSB) and the Southbridge. Some Northbridge also contain an integrated video controller , which is also known as Graphic and Memory Controller Hub (GMCH): examples are the Intel 945, 965, 845, but also several Nvidia. The chipsets are not generic, but specific to each family of processors and RAM, for example, the Northbridge NVIDIA nForce2 can only work with CPUs Duron, Athlon and Athlon XP processors combined with DDR RAM. Instead, the Intel i865 chipset only work in the mainboard based on Pentium 4 processors, which have a higher clock speeds to 1.3 GHz, and that make use of DDR RAM. So, knowing what Northbridge type equipped mainboard, it can knows number and speed of the CPU, but also the quantity and speed of RAM that can be mounted on a mainboard.

In the family of 64-bit AMD processors (Athlon 64), the memory controller that connects the CPU and the RAM is built into the processor, again for the AMD 64-bit, using a single chipset NVIDIA (nForce3) that integrates the Southbridge with an AGP port connected directly to the CPU. The evolution of this unique is the nForce4 chipset, also called MCP (Media Communications Processor). The Northbridge plays an important role in establishing the CPU clock, given that its working frequency is that of the bus (FSB) of the processor, which means that it is not possible to set the base CPU clock different from that of the bus that combines the Northbridge to it. Given that today the operating frequencies of the buses are very high, even the Northbridge chipset gets very hot, so it is normal to see inside a PC a heatsink mounted on it; for the Intel family, this happens since the i815 series. In the notebook you mount the heatsink or, for faster chipset (from i865 onwards) to the heat sink is associated with the cooling fan , usually , to avoid too many fans come together to mount the CPU and Northbridge only one heat sink, which is then cooled by a fan. The Northbridge chipset used more in recent years have , for Intel and the AGP bus, the i815, the i845 and i865, the first two support the processor bus (FSB, 120

www.riparazione-notebook.net Table 7.1 Characteristics of bus employed in Personal Computer since their birth.

Figure 7.7 Block diagram of a PC, with highligted Northbridge and Southbridge; rectangle in the center is the chipset ensemble, that in this case is an Intel 815.

FSB) speeds up to 400 MHz and the third goes up to 800 MHz for Northbridge AGP are, however, always for CPU Intel, i915, i945 and i965, capable of supporting FSB also greater than 1 GHz. The i845 was the first to support the RAM type DDR and had a FSB of 266 MHz and up to 4x AGP, it was followed by the i850 and i865 (also known by the name Springdale), which is was made for the Pentium 4 Northwood and Prescott later on socket 478 that would go up to 3 GHz clock speed. In parallelo to i865, Intel also introduced the i875 (Canterwood) which offered slightly higher performance due to lower access latency memory RAM and system bus. The i865 supported the Dual Channel (up to 4 GB) with DDR -333 or DDR00 and the bus Quad Pumped FSB at 533 and 800 MHz , in addition to pushing the AGP 8x. With the introduction of the ICH5 Southbridge , allowed the management of 8 USB 2.0 ports and the interface for hard-disk S-ATA (150 Mbps). The communication between Northbridge and Southbridge happened on the bus at 266 MB/s. The i865 has had two variants, which have been the chipset i848, intended to cheap mainboard, devoid of the support Dual Channel, and the i875 (improved version). As for the Southbridge chipset, is a chip that implements the ability most slow of a motherboard, is linked to the CPU through the Northbridge and its features include the management of: PCI bus;

ISA Bus (still integrated in modern Southbridge even if the PC is no longer used); SPI or I²C Bus (also known as SM) is used to communicate with other devices on the motherboard such as the manager of the temperature and the cool

ing fans;www.riparazione-notebook.net121 Controller (DMA allows a device under the Southbridge to directly access the main memory without using the CPU); interrupt handler , allowing connected devices to stop the execution of the programs of the CPU ; IDE , S- ATA or P- ATA allow a direct connection of the storage devices in the system; LPC Bridge, and provides the date and control path to the Super I/O (SIO); Real Time Clock, is the system clock keeps the time and thanks to a battery, or write it in an EEPROM and there constantly updated; Power Management (APM and ACPI) creates signals to put the computer on standby (in the notebook turns off the backlight of the screen) or turn off to save energy, both at the request software, either when the user acts on special keys; CMOS - helped by the battery, creates a limited area of non-volatile memory for system configurations (BIOS).

In addition, the Southbridge also includes support for ethernet, RAID, USB, Firewire and audio codecs. It may also include, though rarely, support for keyboard, mouse, serial ports, but normally these devices are connected through another device called Super I/O. The Southbridge is responsible for managing the main power switch and turning on and off the notebook PCs; in fact, provides the power supply charger Power Good signal and can also take care of the temperature reading of the

CPU and the drive of the cooling fans. For this reason, a cold welding or a failure of the integrated chipset or Southbridge (in PC with Northbridge distinct from Southbridge) can prevent the power-on of the laptop.

122 www.riparazione-notebook.netFunctional diagram of an Intel 815 chipset.

The management functions include control of the main power supply and power supply of the individual sections, in order to turn off unnecessary ones when your computer should be put in standby or hibernation (in this case only operate the power supplies of the DDR and the processor, in addition to the power supply charger); in notebook shall also control the enable signal or clock inverter or other circuit which controls the backlight and to disable the video card synchronism signals, so as to turn off the monitor . The chipset communicates with the main power supply/battery charger through a serial bus, such as SPI, I²C and SMBus; all three allow connection with various kinds of device, and consist of at least a line on which pass the data and a clock. In these buses, the chipset is the master unit of the communication (which starts the sessions of data exchange) and the power supply or other device is the slave. The SPI bus exists in two or four-wire: the first has a bidirectional data line and a clock, while the second data lines are two-way, one directed by the master to the slave (MOSI) and the other directed vice versa (MISO), the SPI allows the management of multiple devices. How to I²C-bus consists of a data line (SCL) and a clock (SCK), and can connect up to 256 slave to the master unit, which in the case of the computer is the chipset; each device allows you to set (via hardware by pin or firmware) the address on the bus. The address allows the Master to selectively send commands to the various slave. The SMBus (or SMB, ie System Management Bus) is a variant of the I²C developed by Intel specifically for dialogue among chipset devices such as power supplies and DC/DC, temperature sensors and the lid is opened.

I/O peripherals Under this heading pass the communication interfaces of the computer, which are normally the serial port, a parallel, the USB, have to be added in some cases, readers Flash memory (SD and Compact Flash) as well as Firewire (also known as IEEE1394 or iLink). In most laptops there is also the PCMCIA reader. The serial port, which together with the parallel interface is the oldest of communication adopted by the Personal Computer: consists of a device capable of transforming the parallel data arriving from the data bus, in serial format, called USART (Universal Serial Asynchronous Receiver/Transmitter) or UART (Universal Asynchronous Receiver/Transmitter) interfaced with a voltage levels shifter according to standard RS232-C; the translator converts the data format TTL (0/5V) levels in -12/+12V. This increased voltage allows you to connect peripherals such as printers at distances greater than 20 meters, without that communication suffers from particular disorders. The serial interface has two lines: one for transmit (TXD) and one for receive (RXD); the converter turns TTL/RS232 levels 0/5V outgoing from UART in -12/+12V, while pulses received on RXD, which are of the type -12/+12V, converts them into 0/5V. The UART is the device that is responsible for timing and order in the serial data, to ensure that the device which are directed to be able to reconstruct the byte reordering the individual bits in the transmission that it has put in row one by one. At the receiver, in parallel form rearranges the bits received serially.

UARTs are typically used in PCs of the Intel 16550 and speeds of up to allow communication of the order of 115,200 bps (bits per second). The serial was born in Personal Computer to control printers, communicate with terminals and modem communication; today has been replaced by USB. As for the parallel, is a gate that, as the name implies, makes travel data in parallel form: the data bus of the processor contains only eight bits, since she was born CPUs were only 8 bits. If at one time was facing directly to the CPU bus, today is interfaced via the Southbridge chipset. The device consists of a control chip that provides to some timing signals for the transfer of data in and out; among these there is the strobe, essential to inform the device to which the data is sent who must load a byte. The first parallel (also called Centronics because compliant to Centronics standard) were unidirectional, or used only to send data outside the purpose of controlling, for example, printers, and then were born the current parallel, which are bi-directional, meaning they can both transmit and receive. The parallel is the fastest and easiest of the serial and therefore was preferred to it in the printer control, at least until the advent of USB, the higher speed comes from the fact that data travels parallel and not one bit at a time in a row, then the transfer time of a bit in serial format you can transfer an entire byte in parallel form. Today also this port is in disuse and, like the serial, is hardly fitted in laptops. The (USB stands for Universal Serial Bus) is a universal interface that, unlike the two described above, is used in a wide range of devices as it is a serial device very special, because it works as a bus consists of two data lines (D+ and D-) and an equal power (+ and -) carrying a voltage of 5 volts. The USB is a differential bus bidirectional and allows the simultaneous connection of multiple external devices, up to a maximum of 127 devices (the 128° is the integrated USB controller in your computer ), as well as transfer data to transmit and receive, allows the power supply for peripherals connect to it, providing a maximum of 500 milliamps of current. In its first version, the allowed bus communication speed of the order of a few tens of Mbit/s; 1.1 in the speed went up to 60 Mbit/s, while USB 2.0 is brought to 8 times faster, ie 480 Mbps. The current reaches version 3.0 the remarkable speed of 4.8 Gbps and allows you to power external devices with a maximum of 900 milliamps; must be said that there are very few notebooks to have her on board. The USB allows you to manage a wide variety of devices including pen drive, modem for dial-up and ADSL or ISDN, cellular modems GPRS and UMTS/HSDPA, HD drives, CDs, DVDs, external card readers, laboratory The Firewire interface instead, always as the USB bus, but born purely to transfer large amounts of data your video format and initially adopted by the Macintosh computer to download movies from digital cameras or other computer in its first version allowed a transfer rate of 400 Mbps, and version 2 came to 800 Mbps , and it can also provide power to devices connected to it, for a maximum of 2.5 A. The advent of USB 3.0 will probably slowly disappear this communication device. There exists a variant of Firewire, developed by Sony and named i-Link: it differs because it can not power the devices, but only contains the data line.

Disk controller

It is a device manager able to interface with the chipset hard disk drives, optical or floppydisk readers, portable computers built until about five years ago and had had an IDE hard disk as a link to a connector 40 contacts arranged in two rows 2.54 mm for desktop PCs and 2 mm for those laptops. Born from EDI (Enhanced Disk Interface) developed over twenty years ago, the IDE was the controller for hard disks and optical longest running it and many variations have been developed, known as Ultra-ATA (or Ultra-DMA) 33, 66, 100, 133 (capable of transfer-rate respectively of 33, 66, 100 and 133 MHz) targeted to accelerate the speed of access to data in reading and writing. With the advent of Serial ATA (S- ATA) has become common to call P-ATA IDE drives, meaning that it is hard to parallel interface. IDE controllers have a maximum number of address bits equal to 10, which allows you to address 1,024 blocks of memory, and when the hard disk capacity surpassed the 512 MB the question was to target larger disks and the problem was solved translating the disk geometry. This operation allowed in practice to alter the architecture of the disk, ie simulate a different number of heads and cylinders in order to maintain the number of blocks; the operation was carried out by the IDE controller on board the mother board and the BIOS that the predicted were called LBA (Large block Address) because it made it possible to handle larger data blocks. The controller for floppy disks driver, now virtually disappeared from the notebook because the operating systems can be loaded with disks can be booted

www.riparazione-notebook.net125 from CD and DVD drives, are structurally similar to the IDE, just having an interface with less contacts (typically 34). Currently the vast majority of notebook features S-ATA controllers for hard drives and optical drives to IDE, S-ATA controller interface device is substantially complete control signals for the hard drives. Despite both serial , is capable of reaching very high communication speed , even higher than 200 Mbps In addition to these controllers is the SCSI ( Small Computer System Interface) used very rarely in most notebook and desktop PCs and servers in , it is a bus capable of faster transfer of data, due to the greater length of the data -bus and the address, which allows, for a given data rate, to increase the amount of information in writing and reading. Latest Ultra SCSI controller can reach speeds in excess of 320 Mbps.

Video adapter Also known as a video card or graphics card, is an element of the computer which over the years has undergone a rapid evolution; born with the first PC 25 years ago, was succeeded by the video interface text-only and the Hercules, which in a sense was the first graphics card, albeit with its major limitations. The first video card that could be defined as such was essentially an internal device to the computer, able to transform the data in the CPU information of color or gray scale to be sent synchronized with two sync signals (vertical and horizontal) in order to build images and texts on the screen taking a journey ordered by rows, from the first point on the top left of the screen to the bottom right. This type of video adapter, which in the color version was called CGA, was digital and was limited to output to the monitor binary information on the composition of color or gray scale of each point (pixel) screen, each point was made with a maximum of 4 bits, which allowed the 16 colors or shades of gray. The resolution, defined as the number of points making up each image, was very low: it was about 320x200 pixels or less. The connection of this kinf of board consisted of a plug connector D-SUB 9 pin female, of which four were the data, both sync and a reference mass. And there was the video card analog containing a D/A Converter (digital to analog) can transform analog video signal in the digital data sent from the data bus of the CPU; this graphics card was the EGA, VGA evolved into, with all its variations . Unlike the first , the signal it produces is similar to that of television, even if the frequencies are different. The connection of EGA was formed by the usual 9-pin connector , also used in the first VGA , VGA anyway and higher (Super VGA, XGA, etc.). Was soon standardized on a plug connector D-SUB The resolution permitted by the CGA was always 320x200 pixels, while that of the EGA and VGA went up to 640x480 pixels, followed by the Super VGA (evolution of VGA) 800x600 pixels and capable of XGA, 1024x768 pixels The higher performance VGA video cards have been equipped with DSP (Digital Signal Processor) which is a specific chip for processing of signals able to guarantee high performance in terms of definition (or depth) of the color at high working speed, as those required to compose an increasing number of dots on the screen; compose each screen with a higher number of points increases the sharpness of the image, since the smaller the points from which it is made,

unless it is easy for the our eyes perceive the plot. The color definition is, instead, important to compose the largest number of possible color shades. The use of DSP has allowed us to reach video resolutions of 1900x1.600 points and definitions of the color of 16.8 million colors. As long as the video adapter was digital and characterized by the limited performance, data to build the screens could be sent in real time or with a slight delay from the CPU; hand by hand that the performance in terms of resolution and color depth increased, it became impossible for the CPU and the chip containing the video bus transfer the amount of data required. Therefore, in addition to achieving faster and faster bus (VESA, PCI, AGP, PCI-Express) manufacturers thought to endow the video adapter with its own stow memory where the data blocks for the updating of the images on the monitor screen . This memory could be on board video card or, for mainboard with integrated video card (it is the case of most notebook PCs) part of the same RAM of the processor, which was shared for the video: in practice a portion of RAM (sometimes fixed and other defined through the BIOS setup) can be allocated to refresh the image of the video card, or use for the CPU when the video card does not require a lot of memory. This type of video memory is called shared memory, and the use of part of the RAM for the video card, clearly reduces the amount available for applications, then a PC with a video adapter with its own memory is more faster than a video card which is based on the shared memory. In addition, a video card, however good, if it uses the shared memory is slower than one with its own memory, typically because the video memory chips are much faster (ie have lower access times) than those used in the sticks of RAM. The notebooks of better quality have on board separate video cards located in special connectors, with reserved video memory chips, and sometimes the video card is on the same mainboard, however, has its own video memory, while in the cheap laptops the video memory is shared and is part of the RAM. DVI The various EGA, VGA, etc. they need a D/A converter because the CRT monitors, used until a few years ago had to be controlled with analog signals, with the advent of LCD monitors, which are controlled via digital data carrying location of the pixel on the screen, brightness and hue of each color, the converter is no longer needed. Therefore, after the first years of transition from CRT (analog) to the LCD (digital) video cards that converted the digital data into analog signals, it has gone to video cards that work in a way like the first CGA: send to monitor numerical data, which interprets this to properly position the points on the screen component images to display. This along with the LCD is the best solution, because otherwise it passes from a first digital/analog conversion on the video card and a second analog/digital in the monitor, which complicates video card and electronic monitor, not to mention that degrades the quality of image; in fact, the first conversion (in the video adapter) suffers from a certain approximation and the second (in the monitor) as well. Driving the LCD with a digital signal allows, in addition to the improvement of image quality, a lowering of the costs of the computers and monitors, a reduction of power consumption (due to the minor amount of electronics request), and the possibility of transporting the signal video cables with lower quality than those required by analog monitors are more sensitive to disturbance and the ghosting caused by poor impedance

matching between cable, video card and monitor’s input. In the notebook, the solution was entirely digital welcome in that it allowed the reduction also of the size, thanks to the fact that are required less chips. Since laptops have almost always had liquid crystal display, certainly someone comes to ask why until a few years ago they were used in a traditional analog video card, well, this was done in order to have VGA output for a conventional external monitor, which had to be maintained compatibility. In fact, adapters, video of notebooks, have a switch multi-channel solid state (CMOS) integrated or placed on the motherboard, which allows you to carry analog video signals to the VGA connector, while the digital data directly reach the controller mounted on the LCD. The switch is controlled by a key combination (Fn plus something else…) that acts on the chipset. The video adapter without D/A converter or digital output, is called DVI (Digital Video Interface) and has a connector like the one shown in the Figure 7.10. There are two types of DVI connection: the most complete one, called DVI AD carries both the digital signal, both analog and implies that the video card is both a VGA and a DVI , then there is the DVI- D, which is the DVI pure . In the DVI connector, the four contacts on the side of the blade are those that carry the digital signal, while those on the opposite side carry the analog signals, in the case of DVI AD. It should be noted that there are also equipped with the

www.riparazione-notebook.net Figure 7.10 - Connection used for video adapter equipped with DVI, VGA and S-VHS. 128

Figura 7.11 Zone of a notebook mainboard that includes sound card: audio chip that realizes it is AD1886 by Analog Devices, highlighted from yellow arrow in the picture.

VGA video cards only DVI connector: in this case the connection is used only on the analog side.

Sound Card The audio device is used the computer to play sounds, which can be tones or combinations of notes to give warnings of system, or melodies produced by particular applications or music played by codecs such as MP3, which allows you to store music in the form of digital data with a much higher compression to stow approximately one minute of music in a MB of disk space. Another thing is the speech for the CD-ROM, which can reproduce on their own audio and make it available as a switching output, from which a cable leads him directly to the amplifier BF audio device, already in analog format. A sound card, be it of a computer disk or integrated in a notebook , consists of a decoder (ie, a digital/analog converter, as in the video card) and a group of amplification of the analog signal decoded, in addition to a buffer that brings out such a signal . The sound quality depends on the number of decoded bit sound card: the former were 8 or 16-bit (ISA bus) while the most recent were equipped with PCI bus, 32-bit. Typically, an audio device has to the outside, a jack for audio output from the amplifier taken, one for the audio output taken directly from the output of the D/A converter and one or two inputs to record, and these inputs are one highlevel (line) and possibly one for the microphone, which is arranged to accept low-level signals (a few tens of millivolts). If the card can accept input signals, it has an A/D converter that digitizes the incoming audio and converts it into digital data that the CPU processes and stores in the memory mass unit. Therefore, an audio device is based on a relatively complex chip (LSI) that integrates for the reproduction of sounds a digital/analog converter to the output of which is located a buffer (current amplifier) and a filter to suppress the residual noise of the conversion

(sometimes an active anti-aliasing filter), the output buffer is then the audio output of the chip and goes to the amplifier, which is almost always outside. For the signals acquisition, the audio chip has an input buffer and an analog/digital converter; the voltage levels adaption if the notebook has both the mic input to that line, is performed by a power amplifier external signal to the audio chip. The latter chip communicates with the chipset via a data bus and some control signals.

Network adapter Also known as network adapter or network card is a communication device that allows the PC to communicate with external devices or other computers that sit on a local network. Since it is not the purpose of this volume make a discussion of networks between local computers, we will simply say that the network card is a serial interface that stands out from the RS-232C data management, which are organized into packets sorted according to precise rules, established by conventions such as ethernet (the one used by PCs, notebooks included) or Token Ring (founded by IBM and used for years in the large server to its increased accuracy). Currently, despite its limitations (the data packets traveling all together on the line and often must be retransmitted due to “collisions” that make it lose intelligibility) the Ethernet network interface is the most used; born to communication speed up to 1 Mbps, now goes up to 10 gigabits per second. The ethernet adapter consists of a controller and an interface ethernet adapter impedance, consisting of one or more processors; the typical controller is a device that converts data sent to it from bus (ISA , PCI, AGP or PCI Express) through the supervision of the Northbridge chipset, in serial format and manages the timing of the communication.

Wireless interfaces Fall into the category of communication devices and serve to allow communication of data in serial form, without any wire connection, as it is required for the devices described above (except the ethernet optical fiber, which makes travel data by modulating a beam of laser light) are the IR, Wi-Fi and Bluetooth. Regarding the latter two communication protocols, it should be said that are based on the FM modulation of a radio frequency carrier in the ISM band (around 2.4 GHz) and operate to transmit power between a few mW to a few tens of mW. Bluetooth is basically a wireless radio link, which provides for each device a transceiver (RTX) operating at 2.4 GHz, to be exact, in Europe, the United

www.riparazione-notebook.net Figure 7.12 - RJ45 LAN connector of notebook and desktop PC. 130

States of America and much of the world the frequencies of work are between 2400 and 2483.5 MHz (corresponding channels are located between 2402 and 2402+0+78 MHz). This allows you to carry and use their mobile devices on the go Bluetooth. Each radio channel has a width of 1 MHz and, to avoid the crowding of the channels, the power of the transmitters is reduced to about ten milliwatts, so the scope of the system is reduced to a maximum of 100 meters in the absence of obstacles. The communication takes place according to the protocol TCP/IP and each data string is composed of packets shorter than those adopted by the standard apparatus operating in the ISM band, to ensure greater insensitivity to disturbances, then security of the transmission, which is elevated by the adoption frequency Hopping technology. The latter allows the Bluetooth radio interface to move across multiple channels once established a communication, and what to hook the frequency less disturbed. Another feature of the Bluetooth protocol is the adoption of the technique Fast Acknowledgment, that is the quick recognition of the terminals: substantially, each device identifies the proximity of the other, so that when you want to establish a communication to interested identifies if the call is direct or less to it. From the hardware point of view, every Bluetooth interface integrates a smallpower radio transceiver and a baseband processor, ie a control unit that supports the transmission and reception of voice signals and digital data, both in a point-to-point (two devices that communicate exclusively between them) is in multipoint (a device that communicates with more than one). Towards the inside of the apparatus that equips, every Bluetooth interface communicates via a channel in the base band, that is a kind of very fast bus that allows the transport of data at the speed of modern local networks, and therefore also of audiovisual sampled in real-time. The Wi-Fi interface is substantially the same thing, but change is the power used in transmission, whether the communication protocol, which is substantially that of the ethernet. Wireless interfaces of laptops are typically mounted on cards apart and connected to the mainboard via a shielded coaxial connector and two cables for the antenna, which is essential in transmitting the signal to radiate and receive radio to receive the transmitted signal from the access point or another computer that has a similar interface. With regard to the infrared (otherwise known as infrared or simply IRDA) is instead a serial communication device always , but based on the modulation of infrared light transmitted around the emitter (typically an infrared LED ) located on the side PC or in front or behind , a photodiode detects the infrared transmitted from devices or other PCs equipped with the same connection. To avoid the interference of daylight, emitter and photodiode are placed behind a window covered by a sheet of red/violet. This is an interface virtually disappeared from the notebook and thought initial

Figure 7.13 - Location of RAM (on the left) and for Wi-Fi wireless module (on the right) in a notebook PC.

ly to connect to your computer as mobile phones or printers, all without wires. The roof, meaning the distance at which the infrared device can still communicate with the PC, is of the order of 5 to 6 meters. The infrared port is substantially equipped with an adapter for transmitting infrared LED and a photodiode for receiving, all interfaced with a computer’s COM, the connection can be simplex (transmitting or receiving alternately) ie duplex, in which case using two different carrier.

Modem In many notebooks built between 2000 and 2008 and before the massive spread of ADSL and wireless connections, modem unit was mounted on a board placed separately and inserted through a dedicated connector, detachment from the mainboard was necessary from the hazard of electric shock to the notebook propagated along the lines of the telephone during a thunderstorm. The modem (acronym for MODulator DEModulator) is a communication device, internal or external, even the serial type, which is based on the modulation of transmission in a low-frequency sinusoidal carrier and the reception of this modulated carrier demodulation, this method helps move the data on the telephone wires as does the voice during a conversation. The modulation, which was in the early modem depth, to increase the speed of data communication by 300 bps to 56 kbps permitted by the last line modem, has become a set of amplitude modulation, frequency, and phase .

www.riparazione-notebook.net Internal modem module in a 132

The modem can be divided into two main categories: for line (PSTN) or for pure data line (ISDN or ADSL) in the first case is an integrated circuit that serves to dial the phone numbers , since the modem is intended to be used on ordinary telephone lines. In the second part of this is missing , because the line used is almost always open and connected to the distribution centers of the data that they work as a local area network between computers.

Power Supplies If a desktop PC power supply is unique and should be obtained from the voltages of 3.3 V, ±5 V, ±12V and 5V for the circuitry of standby, the notebook, things are a bit more complex, as its mainboard has to do with part of what makes the computer’s power supply fixed and everything that makes the mainboard of a disk. A modern laptop has an AC/DC voltage derived from a DC component whose value ranges from 16 to 20 volts which powers the computer; the input voltage of the power supply depends on that main network in the country where you use the PC and can be between 100 and 240 VAC. In recent years, largely due to lower costs incurred by those manufacturers and those incurred by the customer for accessories, notebooks are equipped with power supplies that are suitable for all voltage values between 100 and 240 VAC, and this is undoubtedly an advantage for those traveling, that to use your PC may simply replace the network cable or the plug of the latter to provide an adapter complies with the sockets of the nation where it goes. In reality, multi-voltage power supplies have been created by producers in order to build a single type of power supply to all over the world, so as to save on production lines. AC/DC has such a circuit input can recognize the value of voltage supply system when you insert the plug into the socket, it analyzes the power supply voltage and turns on only when it is configured to run with the optimum voltage, so as to avoid damage or malfunction. Inside there are numerous portable power supplies DC/DC switch mode (Chapter 6), each of which is responsible for supply power to a single block of the motherboard, and in a first time the power supply was the main one can extract 3.3 volts, 5 volts and ± 12V for the serial, but then with increasing complexity and consumption of the notebook, it was clear decompose the power blocks appropriately decentralized. The decentralization makes it possible to have power supplies made by small parts, thus reducing the dimensions of the notebook in terms of thickness, because each stage must deliver a limited power, certainly less than it should deliver a single power supply that would serve the entire PC. In addition, decentralizing power supplies can reduce losses in the tracks of the printed circuit mainboard, as, for example, generate high currents close to the CPU it is best to request that transport them throughout the printout, for if a DC/DC should be obtained 3.3 V, the current has to pass from the power supply to 19V mainboard it is about 1/6 of what should pass along the slopes if the 3.3 V were generated near the outlet. A

modern notebook has at least two DC/DC power supply for the CPU, one for RAM, one for the video card, one for the chipset , one for disk drives and one for communication devices such as USB. The CPU typically requires two power supplies, because now from the time of the first series of Pentium processors, in order to reduce the power dissipation (equal to the product of the supply voltage of the chip for the current absorbed) the calculation unit real works at very low voltages, even of only 1.5V, while the registers of I/O are fed to 5 or 3.3 volts in order to be compatible with the logic levels of the internal peripherals to a PC, as well as the RAM, the chipset etc. The voltage that supplies the processing unit is called Vcore, while that of the registers of input/output is called Vio. Since the mainboard of the first Pentium, tensions were imposed by the chipset based on the setting of some jumpers on the mainboard, by the technician who assembled or modified the computer, and then came the chipset able to automatically identify the processor and set from their tensions and the optimal clock (self -setting or jumperless). More exactly, the Vio remained fixed at 5V (3.3 V then, as the increased complexity of processors) while the Vcore could be chosen from 3÷5 V. The differentiation of I/O voltage from core voltage still exists today, where there are processors with Vcore also of 1.5V and logic operating at 3 or 3.3V; Vio and Vcore supply are automatically handled by the chipset, which acts on the two power supplies used for the purpose (between the integrated most used are the TPS51124 and TPS51125). The power supply / charger Immediately after the power input connector (plug) the laptop has a main power supply, which is what is always active and allows the battery charge, when present, it is the main power switch on the notebook, which often provides a provide a stabilized voltage and lower than that of the battery to the rest of the computer, or the DC/DC converter stages, that receive voltages for the CPU, RAM , video card, etc. This power supply is easily identifies primarily because it is the only always under tension and then it has links that lead to the battery, in addition, its control chip (a regulator PWM very complex) is located in the area

www.riparazione-notebook.net Figure 7.15 - Main power supply and battery charger block of a notebook PC. 134

close to the battery connector, except exceptions. In modern notebook power supply controller cooperates with the main chipset, in the sense that it is a complex regulator capable of operating either alone or interfaced via serial connections to bus (I²C bus, SPI, SMBus) with the chipset, it is this the reason why a failure in the chipset can be turned off to a laptop even if you can not find any fault on the power supply components. Usually between the power plug and the power supply first stage is interposed a solid state switch which is nothing if not an enhancement-mode MOSFET in series to the positive line and the gate of which is driven by the logic, or by the chipset or simply by a leg of the main power regulator.

The keyboard It is the element with which the user introduces the data or answers to questions which the PC asks you to answer in order to proceed with the calculations in progress, has been and still is an indispensable element to the relationship between user and machine, because it serves to write text, to introduce numerical data and codes when required, not to mention that virtually all programs for Microsoft Windows and MacOS provide keyboard shortcuts, ie those key combinations that give immediate access to commands otherwise be given passing by the opening of one or more menus. The development of the Personal Computer required to grow the keyboard to issue commands directly to some of the most exploited menu; here is that, from the first keyboards XT has passed to the 102-key with numeric keypad (for AT) to to the modern, which functions can be selected directly from the buttons such as Windows, menu, Alt Graph. The first is to open the Start menu (Start) and the other the context menu inherent to the position of the mouse pointer. as the Alt graph, activates certain characters such as @ for e-mail addresses and Internet the Euro symbol. In laptops as in desktop PCs, there are buttons for the direct opening of Internet browser or the activation of the voice in voice- modem, but also for putting into standby (sleep) on the computer and the subsequent resumption of normal activities (Wake Up). The keyboard is handled by a Keyboard Encoder, ie a coder that reads the pressure of the individual keys, arranged in a matrix and each generates a byte, so the key codes and characters are modular keyboard 256. The encoder output is read by the Southbridge chipset, so if more keys do not work you have to first see if it is a problem of a whole row and then go and check the conditions of Southbridge (the encoder does not fail almost never). The keys on the computer keyboard are buttons that can be magnetic or electro. Are of the first type keys with Hall effect, which is used in computer keyboards fixed a few years ago and were very valuable (and unfortunately expensive…) because it is less subject to failure of those traditional electromechanical contact: in fact, the pressure the key in these devices is detected by the passage of the stem of the button in front of a magnetic sensor, since there are parts in contact, the closure of the keys do not depends on the wear.

The electric keyboards instead rely on a contact that is made to touch one below when you press the corresponding button; for this reason, as simple and economical are subject both to the consumption of the electrodes, both the oxidation of the same, which can lead to elevate the contact resistance to the point that no longer recognizes Keyboard Encoder button closure. The keyboards of this kind are essentially composed of many push button switches as there are keys that compose them. A variant of the keyboard is in electrical contact with the membrane, where there are no push button switches but a rubber membrane containing many carbon electrodes, which when you press the corresponding keys are touching the underlying electrodes, the latter are usually made with the tracks of the printed circuit board on which is built the keyboard, so it is tin or gold plated copper tracks. The same plots are connected by trails that make the rows and columns then connected to the Keyboard Encoder. The keyboards used in notebooks are usually membrane type.

Pointing Device Since its inception, the pointing device of the computer mouse was baptized, probably for that its tapered shape ending with a thin electric wire, reminiscent of a “mouse”, and since then no one uses the more technical name, which has almost disappeared from programs. The name “pointing device” comes from the fact that the mouse is born to work in graphical user interfaces, examples of which are the operating environment of Microsoft Windows, MacOS, Workbench of the now extinct Amiga computers. When it was still writing keyboard commands and struggled with the tricky DOS or Unix syntax, somebody thought how it would be easier to order the computer to perform this or that task simply stating that the distinguishing mark of an icon and pressing a key and this invention became the graphical interface, the way to communicate with computers that has made possible the development of programs once preposterous. The mouse of the laptop can be a trackball, but it is almost only touch -pad. In both cases the pointing device is read by the Southbridge chipset. The trackball is basically a mouse down, or, rather, inverted upside down: its base is inserted in a sphere in a hard plastic material under which there are two rollers, rubber coated and perpendicular to each them, which actuate a potentiometer from which each signal is detected for the horizontal or vertical displacement of the pointer. The ball is bound superiorly by a screw ring that pre By sliding it with your hand, the reels spin for the friction and operate the knobs leading to a similar movement of the pointer on the desktop operating system. As the computer mouse, this device also has a couple of buttons, one used for commands and the other to access the shortcut menu. Why is efficient, the pointing device should be kept clean in the motion detection, so you have to periodically rotate with two fingers the retaining ring of the ball in any direction indicated by the arrow, then pull the ball and place it in a where it can not roll, then with a small screwdriver or toothpick covered with cotton dipped in alcohol, clean the rollers inside from dirt. As to the touchpad, it works similarly to the touch-screen described in Chapter 5: consists of a membrane capacitive organized in rows and columns that detects the pressure, namely the subtraction of electrical charge from the finger; the latter type is sensitive to the fact the user to hold the hand resting on the MPlane the handset , when the pointer moves from

diversmente how’s the finger. The touchpad is unfortunately sensitive to moisture in the environment.

Hard- Disk Also known as the hard disk (or, more briefly, HD) is the mass storage unit that can not miss in a laptop; in fact, some laptops have two (for example HP Pavilion DV9000) of those. The hard -disk consists of a magnetizable disc that rotates at high speed (5400 rev/min is the standard, but there are no discs to 7,200 and 10,000 rpm) on which one or more printheads record the data in the form of magnetic field, on the surface that leaves a residual magnetization in the presence of 1 logical and nothing in conjunction with the low logic level, sometimes the component is composed of two disks: those of the fixed PC, with only rare exceptions (eg the Quantum Bigfoot) always have 2 to three overlapping disks that rotate together. The speed of rotation, together with the switching speed of the chips that make up the interface, determines the time of disk access. In reading, the head magnetizes but not limited to detect the unduzione remaining on the disc surface; reading, such as writing, occur in a spiral, doing move the head from the outside towards the inside of the disc, so that the access to individual logical layers constituting the data are processed sequentially. As it is built, the hard drive is very delicate and just a fall from a height too low (less than a meter) to spoil it because it causes the detachment of disks or platters. The HD for notebooks are more durable and designed to endure the inevitable shock of transport, but if you take a sharp blow while running, it is almost certain that indicate damage. Outwardly, the hard disk appears as a box with solid aluminum base and cover in galvanized steel or aluminum, on one of the short sides shows the connection, which can be, at least for modern HD, IDE or S-ATA (in PCs a decade ago some manufacturers, such as McIntosh, also used the SCSI). For IDE refers to the 40-pin connector on two files (which are normally found next to the other four contacts spaced by 40) which serve to set the Cable-Select or Master/Slave function, and this because each IDE controller on the mainboard supports two units, of which a primary (master) and the other secondary

disk. Figure 7.16 S-ATA disk from bottom view.

Figure 7.17 - S-ATA interface connector of a modern hard

(Slave). Typically, the Master is the hard disk and the Slave player or CD/DVD. The IDE interface has a typical transfer rate (ie speed data communications to and from the mainboard) of a dozen Mb per second, it is followed, some fifteen years ago, the E-IDE (IDE Enhancement) or DMA-33, capable of a speed of 33 Mbps and then the Ultra DMA or Ultra ATA-66 (at 66 Mbps). Since then the IDE ATA began to call and that is why with the introduction of Serial ATA manufacturers have begun to coin the term P-ATA, to distinguish them from the latter. The most recent developments of the IDE interface were the UltraATA 100 and the 133, capable of speeds of communication, respectively, 100 and 133 Mbps. The mainboard capable of handling Ultra-ATA disks 100 and 133 are only the most modern, with Southbridge chipset with bus 100 or 133 MHz, then the mainboard with AGP, the Ultra- ATA66 and 33 are content with chipset bus 33 and 66 MHz, which is the classic PCI. As for the disc S-ATA stands both for the connection, both because, while the IDE communicates with a parallel bus (16/32 bits) that carries the read data and the addresses of the locations where

on the disc are written the same data, the serial-ATA has a serial line, not surprisingly uses less contacts. Regardless of the type of interface, the harddisks exist in three formats, although today it is only found in two; sizes are distinguished by the width of the housing in which they

enter,

www.riparazione-notebook.net Inside view of a generic hard-disk. 138

Figure 7.19 - Hard disk 2,5” size designed for notebook PC.

which can be 5.25”“or 3.5” or 2.5” which is used only in notebooks and in some PC integrated into the LCD screen. The format 5.25” was used by the first hard disk of a personal computer up to twenty years ago, with the exception of the Quantum Bigfoot, built a few years ago, and today the HD are 3.5” to desktop PCs and 5.25” for notebooks.

Optical disk drives This category includes all optical media players used in notebooks, namely the CD-ROM and DVD ROM, whether common or rewritable; also covers the writers (writers) always CD-ROM and DVD. All of these devices consist of a mechanical and electronics, more perspective: the mechanical spins the disc and holds it in place and also provides to position the optic in order to read or write; consists of stepper motors and guides, in addition to a carriage and two plates. The optics includes a laser diode and a photodiode: the first projecting a beam of infrared light toward the surface of the disc and the second detects the reflection, the angle with which this reflex invests the photodiode depends on the depth of the individual “drains” dug in writing by the writer device. The depth of the logic state 0 is different from that of 1, which allows the reader to discern the two levels; recognition is owed to the fact that the reflected beam is presented with a different intensity according to the angle with which arrives on the photodiode. This is true in reading. The recorder writes with a similar tecnique: the laser, more powerful than when it is read, depolymerizes a compound located under

www.riparazione-notebook.net Parallel ATA (P-ATA) interface hard disk, in 2,5” size. 139

Figure 7.21 How optical disc driver works: a laser beam is targeted on the disk surface from wich is reflected with an angle depending from depth of grove that meets; tilt with beam is reflected and hit photodiode determines a different voltage recognized as logoc 0 or 1 of a corresponding bit.

the protective layer of the disc, digging the wells corresponding to logical 1, the photodiode detects the reflection to verify the correct writing. The electronics of the CD, DVD and CD burners is the set of circuits that manage, coordinating, optics and mechanics of the apparatus. The readers and writers for laptops are very small and their tray is opened and closed by an electric motor as in those of desktop PCs: an electromagnet releases a spinet that holds the cart, letting the spring that this has the push on the outside, in order to allow the user to eject the disc. The optical disk drive are equipped with IDE interface connector specific and are usually found on the only controller of the laptop, if the notebook has two controllers, the drive to optical disks are on your own and the HD on another. Such eventuality occurs ever in PC equipped with S-ATA hard disk . Was recently introduced DVD Blue Ray, so-called because it uses a blue laser instead of the infrared, the reason for this stems from the need to increase the amount of data in a writable DVD, only feasible thing -the same diameter of the disk and of layers ( 2 ) available- reducing the size of the drains constituting the individual bits. Since the size of the double-layer DVD had reached the wavelength of the laser and more than this could not choose, it was thought of using a blue laser, whose wavelength is about 1/3 of that of infrared, so also the individual drains can be reduced in proportion.

FDD The Floppy-Disk-Drive is a removable disk drive that conceptually works like a hard drive, only that the disc is removable and flexible; the disc is protected by an enclosure with a window to allow the head of the driver to lean the magnetic surface and detect the residual induction from which to read data. The disc is put in rotation by a clutch mechanism which rests in the central hole of the housing . The floppy disk drive that powered the notebook until a few years ago and was used essentially to boot the operating system. The modern BIOS bootstrap contemplate the optical disc from the unit , then even

for the futility of a device whose media is not allowed to store more than 1.44 or 2.88 MB floppy is no longer used. The storage limit derives from the density of magnetic media (floppy even increased in the past made since the first records from 8” capable of just 128 kB) is used by the FAT, known as FAT12, which with its 12-bit did not allow for direct more than 2048 sectors or memory blocks. In notebooks that have it, is managed by its controller, interfaced with the Southbridge.

Cooling Fan In a modern notebook processor, GPU (graphics processor) and the chipset develop a discrete heat, for which reason require a radiator, almost always overlooking one or more cooling fans which remove the heat, with the fans rotate so as to bring air out from the computer and with it the heat produced. GPU, CPU and chipset can be united by a single sink or radiators have distinct and separate fans. The fan draws air axially or tangentially, through grids or sockets on the bottom of the notebook, but sometimes on the side; eject hot air is sideways. The fans used to cool the heat sinks of the CPU push the air outside through the heat exchangers, which are the ends of the finned heat sinks of CPU, GPU, etc.; in this way the air removes the heat from the fins, which is then dissipated more smoothly. The cooling fan is governed by a static switch that turns on and off as necessary, or by a PWM controller which allows the variation of the rotation speed, to manage the fan provides an integrated thermal sensor, which usually has an interface I²C-Bus to communicate with the chipset and inform him of the events thermal of the CPU the chip may use an external temperature sensor placed under the CPU, or, in CPUs that are provided, the internal sensor to them, which is usually a diode placed in the same semiconductor chip and is accessible via the two feet. A typical temperature sensor with I²C bus for communication with the chipset is the MAX6657 from Maxim, ie the MAX6658 or MAX6659, in the same case: it is a sensor capable of both informing the chipset of the stories thermal of the CPU, both of responsible for their own fan control above a temperature considered critical. Another component that performs a similar task is the ADM10342 of ON Semiconductors: it is a manager of temperature with internal sensor but capable of using thermal sensors outside , this also interfaced via I²C bus and has outputs for fan control via the transistor. The fan or fans used for cooling the notebook are typically equipped with a

Figure 7.22 - Application diagram of MAX6657 integrated circuit: this component manage one or more cooling fan and

communicate with Northbridge

Figure 7.23 Cooling fan mounted on a heatsink that cools simultaneosuly CPU, GPU and chipset. On the three components is stand aluminium plate soldered on welded with a copper tube containing refrigerant gas wich movew by convection and transfer heat to heatsink.

speed sensor, which can be seen by looking on the connections: in fact, the connector has three contacts and many are the wires that come out from the body, two of which are positive (red) and the negative (black) of the motor, while the third (yellow) is the output of the circuit or the speed sensor, used to communicate to the integrated thermal sensor or the chipset of the computer the speed of rotation of the fan. In practice this wire comes out from an electrical signal to a rectangular wave whose frequency is directly proportional to the speed of rotation, ie typically matches the number of revolutions per second made by the rotor of the fan. From time using fans with tachometer sensor because they allow the chipset or the integrated operating the cooling test the speed of rotation and then report any issues into the vents with special video alarms or lock your computer (in PCs that provide this function).

Battery The rechargeable battery (battery) is a reversible electrochemical device, whose basic structure consists of two plates of the same metal immersed in a liquid or a jelly said electrolyte; the easiest battery has lead plates and the electrolyte in it is acid dilute sulfuric acid (H2SO4). In resting conditions, the voltage of a battery cell is about 2V; grows during charging and decreases during the discharge (to obtain a battery of 12V must therefore connect six cells in series). To see how the battery works, suppose we pour into it the aqueous solution of sulfuric acid (H2SO4) where there are ion SO4— (sulfate ion) and ion H2++ (hydrogen ion). Immediately the acid attacks the surface of the electrodes forming lead sulfate (PbSO4) and leaving wealth of H+ ions (hydrogen) in solution. Applying a potential difference to the plates, to the negative pole rushes hydrogen, which accumulates making the porous element; positive pole arrives SO4, which loses the negative charges, reacts with water and reform H2SO4 (which is decomposes again into ions) plus oxygen. The dissolved oxygen combines with

). The charge is complete when the plate with lead dioxide (positive) can not oxidize and lead to porous sold all of the material that the solution could accept. The two plates are now a porous lead (with hydrogen) and the other of PbO2 ; the two plates have a potential difference of intrinsic and then, if it disconnects the generator and are connected with a wire, electrons move from one the other: Lead, enriched with hydrogen (negative) sends electrons to PbO2. The discharge would be short lived but becomes positive lead that come negative SO4 ions that are in the solution. These are neutralized, they react with hydrogen and give rise to new H2SO4, and it remains so metallic lead of departure. The lead dioxide, receiving electrons from the solution becomes negative and attracts the H++ which combine with oxygen to form water and leaving the Pb. So the two return electrodes of lead as in the initial conditions, immersed in sulfuric acid solution. If the charging voltage continues to be applied even when the accumulator is now loading, electrolysis of water occurs, which produces hydrogen and oxygen at the positive pole to the negative pole; this gas mixture can be explosive, and therefore the charging must be done in ventilated areas. For accumulators are defined, in addition to the nominal voltage (2 volts to element) the discharge current cold and capacity: the first is the maximum current at low temperature (typically below 20 °C) while the second is the ability of storing electric charge and is expressed in Coulomb (ampere x second) or, more commonly, in Ah (ampere/hour). In this regard, consider that 1A/h is 3.600 Coulomb. The batteries do not exist only to lead but are made with different materials and having considered their weight , the type just examined is relegated automotive application, inverters and UPS (uninterruptible power supplies) and some machinery and equipment fixed. For applications where you need a better ratio of weight (ie footprint) and capacity, were built accumulators in the first instance to nickel-cadmium (NiCd) then abandoned because afflicted by the memory effect (get used to the charging regime usual, then if they are loaded usually at less than full charge lose some charge capacity) in favor of NiMH (nickel-metal-hydride) and the most modern Li-ion (Lithium Ion) Li-Po (lithium Polymer) and LiFe (lithium-iron). The batteries used in modern laptops are lithium-ion or Li-Po, although until a few years ago would use the NiMH batteries. Each cell provides 1.2V NiCd and the same goes for NiMH, lithium-ion batteries (Li-ion then, Li-Po and Li-Fe) each deliver 3.6V, then to form a battery pack it serve less. Lithium-ion batteries are certainly the best in the aspect of storable energy density and discharge current that can be delivered, but is more expensive and should be handled carefully, due to heavy discharge currents (in excess of the maximum allowed) lead to a strong overheating and the fire or explosion, and the same is true if in office are not complied with the required parameters. Therefore, the charger notebook must be designed for the specific type of battery used, though in reality many laptops are equipped with charge controllers called “Multichemistry” because they are able to charge NiMH, Li-Po or Li-Ion Chapter 7

Figure 7.24 Li-ion type battery for notebooks (in the picture, battery is spare part for IBM X200).

simple. The integrated charger that govern their stored charge curves typical of these batteries and know how to detect the end of charge so as not to exceed the permissible current. The NiCd and NiMH batteries are typically formed by several elements (8 to 12) placed between them in series and possibly accompanied by a circuit that indicates the state of charge or has a resettable fuse that limits the current supplied in discharge or that absorbed in office, the Li-Po have often instead of taps which serve to balance the individual cells. In other words, because if you put these batteries in series can not charge all the same, the battery pack you insert a circuit called “load balancer” which divides the charging current of the various elements, partially bypassing those who are already loads in favor of the elements that have a lower voltage and therefore require more current for charging. Thus, the battery packs Li-Ion and Li-Po are more complex because they often integrate the balancer of the elements; sometimes this circuit in the charger on the notebook is off, then the battery has, in addition to the positive and negative contacts three taps (typically a lithium battery pack consists of three cells), each of which gives access to an element and allows to monitor the charge. In addition to the charging circuit and balance , usually in packs with lithium is introduced limiting the output current , which is used to avoid the explosion of the accumulator where a short circuit inside the notebook tended to be absorbing more of the output current, the limiter may be composed of a resettable fuse or by a real electronic circuit to exceeding the maximum permissible current disconnects the output (ie, the positive terminal) for a few seconds or until you press a special release button placed outside the battery. This complexity due to the integration of an electronic search, greatly increases the cost of lithium battery packs, but they are appreciated for the great autonomy granted to the computer.

CHAPTER 8 EQUIP ITSELF TO REPAIR NOTEBOOKS Fix mistakes in notebooks requires the preparation of a minimum of equipment and the availability of a workbench possibly with a bracelet with chain for the mass discharge of static electricity. On the table will need to have a certain amount of tools and equipment that vary according to the laptop to be repaired and which are used primarily to remove and refit the outer and inner parts, as well as to remove certain constituents, they must not miss screwdrivers of various sizes in and cross -cutting, as well as torx keys, allen, wire cutters and pliers for electronics, tweezers such as those for medication and anything specific can be used for computers that from time to time arise. As for the electronic equipment, you need to have on hand at least a welder from 20 to 25 W or less and a desoldering iron or tin suction pump tool, a hot air station and a processing chip BGA; complete the experience a magnifying glass enlargement or a lamp with a built-in lens, necessary because when soldering chip with feet close together it is difficult to see with the eye if there were no short circuits, and a table lamp powerful enough to illuminate the work area well. Instead of the normal welder, it would be better to use a welding station at the pond with electronic temperature regulation; some stations have a desoldering depression, formed by a tool similar to a soldering iron, the tip of which, however, is hollow and communicates with a tube leading to a vacuum pump. Besides that, it must be the solder based on tin and lead, or (now that the RoHS standards require, for the electronic calendar, the adoption of lead-free alloys) a solder alloy of another kind, free of lead; also serves as the flux, preferably in the form of paste. The flux is a chemical that facilitates the melting of solder and facilitates the distribution and adherence to the components to be welded. It also serves the desoldering braid, which is a sort of strip of wire mesh copper imbibed flux of a substance that captures the pond , allowing to remove it very well by the pitches and the welds around the leads and metallized through holes where these pass. Below we will describe the electronic devices mentioned above, you also will mention measuring instruments that should be present in the laboratory of a repair technician: in particular, to the tester and oscilloscope.

The iron welder We start with the soldering iron, which is a simple tip variously shaped (with a grip to prevent there being burned hands) whose purpose is to melt the solder that connects the electronic components to the printed circuit board of the computer or the connecting wires to the connectors; to do this, the tip is in turn heated internally by a resistance, now always “armored” (covered by a stainless steel casing) on which sock. The tip can be coated copper (silver) or stainless steel; the first heats more quickly but lasts less, since it is formed from a softer material and that is consumed to quickly due to the pressure and the rubbing on the areas to weld. The steel tip is more durable, although the thermal inertia of the material makes it a little slower to heat up. The welder for electronic work for brazing and is built to operate at temperatures typically between 230 and 400 °C, as it serves to melt the solder based on tin and lead (or even the

alloys Rohs compliant, that require slightly higher temperatures). The welder has typically a cord terminated with a plug that allows the power supply with the mains voltage (220 Vac) and sometimes has a button to operate at half power, which allows you to choose between two soldering temperatures. The welders for electronics have power, typically ranging from 20 to 50 watts. The classic welder reaches a temperature that is not always the same but is affected by many conditions, not least those environmental (temperature) and the rush of the mains voltage. To perform welding at a temperature stable and known, it is necessary to use a soldering station, which is composed of a welder and a block that controls the power, the control is effected in various ways but

www.riparazione-notebook.net A basic welder for electronic:inside of the of his tip there is a resistance wich can make them reach a temperature high enough to melt tinbased solder alloy. 146

is always based on a sensor placed on the tip, the purpose of which is to inform the control unit of the temperature reached. The system is of type thermostated, so that when the set temperature is reached, the resistance of the welder is deprived of food and back energized as soon as the temperature drops a few degrees below the set value. Soldering stations there are of various types, but all operate according to this principle, some works at a fixed temperature and largely comprises a selector to set two or three temperatures or a knob or a panel buttons to vary the temperature in liking. The most valuable stations have a display (LCD or light emitting diodes) are shown where the operating parameters, namely the set temperature and that of the tip or only the latter. Use of the welder The welding or brazing tin consists in joining two parts (in this specific case the terminals of the electronic components and the wires or tracks of the printed circuit) which are typically of copper, by means of a certain amount of lead or tin alloy Rohs compliant: heated up to the melting point, the tin drip on parts and when it cools the fixed one to the other, establishing the necessary electrical connection; however, since the solder is metallic and therefore very conductive. In order to improve the grip of the tin alloy, normally the terminals of the electronic components are dipped in the factory and is therefore that appear silvery gray color. Because the welding is well requires that the surfaces to be welded are neither wet nor oxidized; also, again to improve the adhesion of the solder within the wire which constitutes it is encapsulated flux, ie a gelatinous substance (more or less dense) that warming liquifies and has the dual effect of improving the fusion of the pond and adhere it and thicken on metal areas, so it ends up on the pitches and the terminals of the components instead of short-circuiting adjacent plots. The welding is conducted by placing the tip of the soldering iron for a few seconds on the copper track where it has been stuck (in the case of mounting leads through hole) or placed (if it comes to mounting surface) terminal of the component to solder and then placing the solder wire on the terminal or on the pad.

Solder of a component on a printed circuit board using a welder for

electronics and a tin Figure 8.3 A welding station equipped with a little sponge to wipe tip of welder.

We must not rest on the tip of the wire or at least not have to do it before you have warmed up the track and terminal, otherwise it is easy to occur the socalled “cold welding”: in practice, the parts appear to be united but are not, and the electrical resistance of the contact is too high to ensure the proper functioning of the circuit. The cold welding is very insidious because hardly visible, because the component seems welded but it is not: it occurs because the melted tin alloy drip on the warm parts (track and component ) that are not hot enough, then comes solid too quickly and does not grip as it should. The aim should be remembered that the pond is well melted recognizes, in addition to its liquid form, for the color, which becomes shiny silver; when cooling and returns solid, tin passes suddenly from glossy to opaque color.

Tin suction pump It is a more or less sophisticated apparatus whose purpose is to suck-in the tin of the welds; is particularly useful when it is necessary to unsolder electronic components in traditional mounting (THT, Through Hole Technique) with many pins of double-sided printed circuit boards with plated through holes, given that the welder here is not enough because the pond remains in the interstices between the terminals and the walls of the holes. In its simplest form, it is a hand pump formed by a hollow cylinder containing a piston which is loaded with a spring and pressing a button returns to rest, sucking the solder through a spout of metal or of teflon communicating with the chamber of the blower. This tin suction pump, which is mechanical, it is used in conjunction with the

www.riparazione-notebook.net How to use desoldering braid to remove tin alloy form a printed circuit board 148

soldering iron: the latter merges the tin to make it removable and tin suction pump sucks him. Since hold two tools is inconvenient, were invented desoldering, which are suction pump provided of a metal (copper or stainless steel) tip heated as in welders. In them, the cylinder communicates with the tip heated by an electric resistance and internally hollow. The tip heats and melts the soldering alloy and the pump sucks him; clearly the thing works if the operator is pressing the release button on the pump when the pond is well melted. Tin suction pump can be a real machine, often integrated in the welding stations: in this case it is a desoldering iron like the one just described, but which lacks the hand pump, because the interior of the hollow tip is connected to a rubber tube that ends at the base station, in which there is a vacuum pump to the service technician activated by simply pressing a button in the handle of the desoldering. The pump is electrically driven and can suck continuously, differently from that of common desoldering, which aspires only once and then be recharged and for this reason the soldering station with desoldering iron is also more effective in removing large amounts of tin. Maintenance of tin suction pump The pond aspirated almost immediately cools and solidifies, forming more or less large masses that have to be stopped before reaching the suction pump; purpose, within the desoldering is a mesh filter or formed by a cotton swab uncompressed, in order to let air pass through but retain the pond. Over time and with a frequency that depends on how you implement, the filter must be removed and replaced with a proper . Moreover, especially if it is made of copper, the tip tends to form scale due to failure of the inner wall due to the heat and with time becomes clogged; therefore should be cleaned using a pin or the thin iron wire , or special cleaners supplied the desoldering iron by the manufacturer.

The hot air station

www.riparazione-notebook.net A soldering station with electrical tin suction pump integrated (JBC); it is designated for professional use. 149

It is a machine that heats the soldering or unsoldering components or their connections by means of a hot-air jet, of which can be adjusted, by controls on the front panel, the intensity (the pressure, in practice .. ) and the temperature . This equipment is necessary when you need to remove SMD components with many pins or very small, or with very thick pins, since in these cases only proceed with the soldering iron can damage components or make impossible in practice the soldering of integrated circuits that have large number of pins and pitch very small. Even the desoldering serve little, as more suitable to unsolder and integrated components to terminals passers; with SMD components, would fail to remove the pond under the pins, so do not allow to detach the components from printed. The hot-air jet station consists of a fan or air pump of the rotary type with low pressure (always controlled by an electric motor), which draws air from the outside (protected by a filter) and blows it into a tube which leads to the head of the dispenser, the latter is a tubular nozzle which can be variously shaped or have a cylindrical shape but be prepared for the application of adapters (deflectors) able to direct the air in various ways. The dispenser has a handle that allows the operator to athermal hold it and direct it where you need it. Modern hot-air stations have the heater in dispenser head: is a resistor that receives power supply from station, which provide also cold air produced by the same pump and carried via the same tube. Normally, in the head are placed a termocouple and a thermostat: the first provide a feedback to control board to ensure stabilised temperature and the second protect from overheating. The desoldering hot air is easily done by placing the card to rework on a metal plane from which loosen the components and directing the stream of hot pin on all sides, passing in sequence from one to another, and when the soldering alloy is to blend becomes shiny and it is then that you can remove the chip. In order to have, with a steady hand, hold it with tweezers such as those for dressings, lifting it with the decision and taking care not to hurt the components that are located next to, because if the item you disconnect is in an area of densely printed circuit board “populated” components, it is easy that even those around

Figure 8.6 - www.riparazione-notebook.netA hot-air station (on the left) and one of it’ air deflector designed to desolder BGA or chip carrier: nozzle is square and direct hot air sidely and on top of chip. 150

are heated enough to melt the solder, which means that you just bump them to tear and make a small disaster, because the drag of a component causes the shedding of the pond and the short circuit of trails and nearby components, then difficult to remove. The desoldering succeeds better if the circuit is placed over a hot plate, in that, while with the only hot air can be heated on one side and then must reach very high temperatures prior to obtaining the dissolution of the solder, heating from below is printed prepares the pond to the merger, which may occur with a lower temperature on the side invested by the jet of hot air. It benefits the life of components and welds, for if one side of the printed matter is heated strongly than the other, the difference in temperature can make buckle and warp or circuit disconnect of welds, while the printed uniformly heated this risk does not exist. As for the welding, hot air machine is also useful in this case for components with many pins or for those too small to be welded with the traditional welder; course the machine lends itself to replacement of the components, in the sense that welds quietly chips provided that the slopes on which their feet should abut are properly tinned. The welding is done very simply by placing the chip on their pads, well centered with respect to them; placed the component, you can warm it up, making sure that this time the hot air must be pretty weak, otherwise if it’s blowing hard can move the chip, especially if this is small. In fact, while when it comes to desolder a component can also increase the power of the jet to increase the temperature rapidly, caution should be observed here. The welding does best if before placing the component is deposited on a thin layer of flux plots: in fact, this material facilitates the fusion and adhesion of solder around the prongs of the chip, thus preventing it from going to shortcircuit neighbouring contacts. Even in the case of welding, the operation succeeds best if the form is first heated by a plate. The hot-air welding can also be done on copper tracks clean, but first we need to stagnate the pitches on which the pins of the components must adhere to; usually the flux will make things easier.

Figure 8.7

Cautions when use of hot -air machine Some hot-air jet machines (eg Velleman) have a system of off-delay that allows the heater to cool down when the user turns off the machine; substantially after manual switch off the fan continues to blow air for a certain time, up after cooling . This means that if you directly supports the dispenser from its nozzle exit for a while hot-air and then if you turned off the machine when he was at very high temperature, it can be dangerous. For this reason, you should never place the dispenser on a table or in front of combustible materials (solvents, alcohol, paper) or deformed by heat (polystyrene and weak plastics), but rather put it on its stand. This precaution also applies to machines off immediately, when we want to temporarily support the dispenser for a moment because we do not need and do not want to turn off the machine (for example because it is one of those where every time you turn you have to reset with the buttons temperature and air pressure) , but in any case make sure that the support behind the dispenser there are no flammable objects or you can dissolve.

BGA rework machine It is more or less complex equipment, which allows the soldering and desoldering BGA chip with connections, which , compared to the classic DIP, TSSOP, chip-machineries and so forth, do not have the contacts laterally, but bring them back under its body and for this reason, a chip BGA is joined by heating after having placed the corresponding pitches well centered and after heating the printed circuit board. In this case the centering is of fundamental importance and is obtained by the references made in the PCB, which must, therefore, be made as accurately as possible, in more complex machines, the BGA is positioned photographing with a digital camera the position of the contacts on the printout, then superimposing the grid that they make to the vision of the chip when it is leaning on the same printed. In any case, usually just place the BGA so that all its sides covering the contacts, namely that they are equidistant from the silk-screen mark; when the spheres of solder melt, the BGA is automatically positioned on the contacts of the circuit. In order to weld the contacts of the BGA are equipped with small balls of solder that the manufacturer at the factory applied hot on every pitch, and the heat of the form and that it is subject to the integrated melt the alloy, which adheres to the pitches it and the corresponding PCB, making attachment and electrical connection. In order to facilitate the adhesion of the pond in the right places, before placing the chip is deposited a thin layer of

flux paste on the related pitches on the printed circuit board; the flux must be specific to the BGA, so it must be thick on average. The welding is normally effected by heating the printed from below and from above, but in this case only in correspondence of the chip to be soldered. It can also be welded more integrated, simply by placing each in their place and then heating initially the lower part of the circuit, then in a second time also the upper one. Normally, the welding of the BGA involves heating the lower side of the printed so that the upper ports is at a temperature of about 140÷150 °C; reached this level, it begins to heat also the upper part with a powerful heater rapid, that the door to a temperature between 200 and 230 °C for a predefined time from the factory on the basis of various parameters. In fact, it is enough to reach 200 to 230 ° C only on the components to be welded. Since the components may move, the majority of manufacturers of notebook fixing the BGA through one or more points of glue resistant to high temperatures or with epoxy resins; this is done before starting the heating cycle. Just these glues are the cause of the difficulty of rewelding of some BGA chips when you have to repair a laptop. The critical assembly of BGA makes it difficult to replace, not always, without the proper equipment, is successful, which is why it is better groped before the reflow. The machine for BGA is used largely for the reflow process, which consists in “wipe” the welds with the help of an adequate amount of specific flux for reflow, which is quite fluid (low density), the machine serves then in repairs, which, however, are the most frequent, notebooks. In fact, more and more components are used BGA (who began to make their appearance in the tabs of the PC with the LX and BX440 chipset mainboard of the Pentium II), especially for chipsets and chipsets are now responsible for the government of a large part of the operation of notebook, the power-on control and power memory access etc.

Figure 8.8 - Machine for soldering and desoldering of BGA’s; the one on the left have lower heater based on a electric resistance, and the upper based on a IR lamp. Machine on the right is a professional type, with electronic control and upper heater based on a hot-air jet; lower heater

uses an infrared plate.www.riparazione-notebook.net153 The simplest machine consists of a horizontal plate metal or ceramic material heated inferiorly by an electrical resistance (isolated from ceramic material): a kind of plate for sandwiches or electric grill, this plate is mounted in a structure that contains two guides on which there are two adjustable supports for supporting the printed circuit board on which to operate the heat treatment. The same base that supports and guides the plate has an arm (which may be of various kinds) that suspends a quartz lamp that emits a powerful light and a large quantity of infrared, it serves to heat the upper side of the printed circuit. To avoid reaching high temperatures or to keep the coldest parts of what is required for the success of the weld, a quality machine must have two probes to be placed on a top surface of a printed circuit board and the component to be heated; each probe must be connected to an electronic thermometer capable of communicating to the operator the temperatures reached, so that these can turn off the heater of the side that has exceeded the optimum temperature range. The best machines are thermostated in the sense that have two thermostats, each of which uses one of the probes to detect the temperature of one side of the printed and keep it within the limits provided; each thermostat is usually of the electronic type (but is not except that you can find electromechanical thermostats bimetal strip) and has buttons and displays to set and display the temperature reached. The thermostat is a device that keeps the temperature set in it, catching it by means of the probes. Also in the machines of good quality, the heater of the lower side is infrared, the upper can be the usual quartz lamp, but also, in models particularly valuable (and expensive) a metal bell that blows hot air directly on the BGA. Some machines also include a suction cup (a vacuum system) capable of sucking the chip BGA and lift it when the tin alloy has melted; this kind of equipment is used, of course, to extract the BGA and replace, but it is not necessary for the reflow. Furtherly, the higher performance machines have three heating systems: a lower infrared or resistance, which heats the machine; one, always lower, blowing hot air under the chip; in these machines can be set separately the temperatures of the three heaters. In machines for welding and rework of chip BGA, the heating of the lower side must be done slowly and still respecting the properties of thermal inertia of the printed circuit: otherwise before the temperature rises to above 140÷160 °C required, under the temperature can reach also to more than 220 °C and begin

www.riparazione-notebook.net Flux paste it used to spread (with a little brush) on the sides of BGA first to start with reflow or removing procedures. 154

to melt the solder, with the result that if there are components may break off, with the result that in groped to repair the machined is damaged beyond repair, unless you have the maps arrangement of the components (that no manufacturer provides), and go back to weld the elements one by one broke away from the board. The heating plate must therefore operate so as to raise the temperature gradually, so that the difference between the lower and the upper side of the printed matter is not excessive; in other words, the lower heater must leave at the time printed on the upper side of heat more or less as it warms up the upper one, otherwise when the latter has reached the temperature at which the heater can be turned off, maybe the bottom side will have already reached the critical temperature.

Laboratory instruments A good technician can not ignore the knowledge of the traditional instruments of measurement and analysis used in an electronics laboratory, and this, in order to analyze what happens in the circuits of the notebook. Below you will make some mention of the measuring equipment, the first of the inevitable tester, multimeter, or if you prefer, the latter is the basic instruments that must not be missed on the bench of an electronics technician, as in the work bag an electrician. The drastic reduction in prices due to massive invasion of the products in the Far East now allows anyone, even to the experimenter more “penniless” to have a multimeter in the house, which now also be bought with a few dollars, of course; the fact remains that there are instruments and instruments: Fluke, Philips, Beckman worth the money they cost, as one of China, very little money, certainly can not be considered the essence of reliability, even if all goes well when not in use a great accuracy. The multimeter It is both a voltmeter, an ammeter, and an ohmmeter can also become a good gauge of inductors and capacitors, transistors and an analyzer. The tester allows measurements between two points and, therefore, mainly two bushes where tuck the wires of two probes, the tips of the electrodes are well coated with insulating material calculated to avoid the shock of who holds them between his fingers, from place in the points between which must perform the measurement. Normally the instrument measures voltages and currents in both continuous or alternating, typically at mains frequency can also measure variable magnitudes at higher frequencies (up to a few kHz) but is designed to read a sinusoidal components. This is because the measurement of the alternate takes place by adjusting the current through a half-wave rectifier, the capacitor which, in the presence of an alternating sinusoidal waveform, is a voltage equal to 1.414 times the RMS value. If you go to measure a voltage of different waveform, such as the

CPU clock, the signals present on the inductances of switching power supply and other parts of a computer, the value obtained may not be the exact one. To make measurements on complex signals must be rectangular and the oscilloscope. The measures also switch the frequency of the voltage or current to be measured has its importance: the tester is optimized to make measurements on relatively low frequencies. Measuring voltages and currents at frequencies substantially higher, do you feel the effect of the capacitor used for the filter, which, albeit small value, attenuates the voltage sent to the microammeter proportion to the frequency, and then with a tester is not expedient to measure voltages and alternating currents over 1 kHz. For DC measurements should be respected polarity, ie the positive lead (red) to the most positive and the negative (black) on the contact less positive or negative of the circuit; for those on the AC test leads can be connected freely (red and black have no meaning). The same goes for resistance measurements. As a tester you can not properly represent all measurable values, each type of measurement is divided into courses, ie measuring ranges, a flow is the excursion between the minimum and maximum voltage read on the graduated scale. It defines the full-scale range of a value that brings the needle at the end of the stroke, so if a range is from 30 V full-scale (fs) means that the tester can measure, placed in it, up to 30 V. As far as the digital multimeter (the only one today on the market) is based on a continuous numerical voltmeter capable of measuring even a few tens of millivolts, equipped with analog/digital converter and driver for liquid crystal display 3 digits sign. To make resistance measurements, the voltmeter is connected internally to a stack and the milliammeter or voltmeter with LCD is placed in a measuring bridge. The display of the instrument provides the numerical value and in some case also shows the full-scale chosen and the unit of measurement which the reading refers. To make good use of the digital tester must first know how to make up the LCD display, which, in the most common form to multimeters (especially those “basic”, ie those of low-cost) is divided as shown in Figure 8.12. The indication on the display is always four digits, although the three are whole right and

the left half is (here is where does the term 3 digits), in other words the first three digits can display any number

Figure 8.11 - Main components of command panel of digital multimeter: 1. FUNCTIONS & RANGES SELECTOR; 2. COMMON PROBE BUSHING; 3. VOLTAGE & RESISTANCE MEASURE BUSHING; 4. LOW CURRENT MEASURE BUSHING; 5. HIGH CURRENT MEASURE BUSHING; 6. TRANSISTOR-TEST SOCKET; 7. CAPACITANCE MEASURE SOCKET.

from 0 to 9 and the fourth only 1 (if the reading is off you can see with the first three digits). To the left is the minus sign, which turns on only when the indicated value is negative, to be clear, it is only in DC measurements if you connect the leads in reverse, ie if the red and black is on the negative to the positive. It may also appear in the ohmetric measurements, if the circuit in which the measurement is made is fed, or if there are capacitors capacity remained significant loads. In addition to three and a half digit and the sign, the display always shows low battery indication: the message LOBAT appears when the battery is low and does not PROVIDE enough voltage to ensure correct measurements. If there is, it means that you have to replace the battery as soon as possible, which is usually 9 volt . This is in the typical equipment; must be said that the high quality instruments reports, on the display, additional information. And not only Autoranging multimeters, not having selectors for measuring ranges, display the measurement, the indication of AC or DC, or resistance. For example, some testers display the type of measurement: if it is resistance, A=(or mA=) if you are measuring a DC current, Arms (or mArms) or something similar (eg A accompanied by the symbol alternating ) if the measure is alternating current, V=(or mV=) if you measure DC voltages and Vrms (or mVrms), or accompanied by the symbol VAC if the measure concerns an alternating voltage. Still, if you are making appears Hz frequency measurements, µF or nF if you are measuring capacity and mH or µH if you are measuring, however, inductances. The tester described so far is manual, because in it we select with a rotary switch or bushes measurement type and scope. The market, however, offer special automatic digital

multimeters that are able to decide for themselves what is the scope that best fits your measurement: those are called “auto-range” because they choose for themselves the scope and sometimes the type of measurement. Typically, these instruments have a selector to choose whether to measure voltage, current or resistance, to the extent of voltages and currents, the tester recognizes itself if it is AC or DC. Like any digital multimeter, this has distinct bushings for different measures. Typically, the auto range function is active for voltage measurements, but does not apply to current measuring ranges with a strong current, for which there is a separate circuit to use manually.

Typical arrange of digital multimeter display: the wording on the top on the left (LOBAT) appear only when battery are near to

Use the multimeter The digital multimeter is turned on by an ON/OFF button, or by moving the rotary switch to the position corresponding to the measurement to be made. Some models switch on and off with a button (but are always powered, even though consumption at rest as well as to make a battery last more than one year) and go off by yourself unless used for a number of minutes. When it makes measures, well remember these simple rules: need to touch parts (tips of probes) metal on the points where you want to read voltages, currents, etc.; avoid touching the metal parts with your fingers, because in the best case the measure distorted and at worst risking your life, your fingers have to be always and only on the handles made of rubber or plastic; always fasten between the thumb and index fingers (keeping behind the average) test leads and place them firmly on the points where do the measurement, making sure that they can not slip off and go short circuit; always replace the probes that presented cracks on the handle or the leads which may expose the wires or metal parts.

Figure 8.13 - Digital auto-range multimeter: rotary switch selector serves just to set kind of measure, while range is selected automatically. The bushings are, in this case, three: common, voltage/resistance, current. For the current measure, input is only one, because current are sensed by a unique shunt resistor. The auto.range multimeter display shows kind of measure, and if value is referred to a contin

Voltage Measurements To measure the voltage, you must use the negative probe to the bush common (COM), or if the instrument has separate sockets for measuring DC and AC, use = in the first case the bushing and the second one with the symbol AC (~). Regarding the positive test lead, you must insert the spinet in the bushing V if the multimeter is of those with the selector (the bush for the measurement of voltages is always the same, both for the measures in that continues for those in alternating, at least in instruments with switch/selector) or in the bush corresponding to the reach if you have a meter as a bit dated, they have a bushing for each course and for each measurement type (AC or DC). Before making a measurement crave to know what can be the maximum voltage in the circuit and make sure that the tester can bear it about you notice that on the instrument or in its manual is always indicated the maximum voltage applied at the voltage measurement or the bushing range coulometric higher. This voltage should not be confused with the maximum showable (full-scale range of the highest) but it is understood as the bearable limit from the meter without damage occurring in his circuit. Measurement of continuous currents When you have to measure a current, such as that supplied by a battery or a power supply, you must have the multimeter on the current measuring ranges. Before you see the details, it is appropriate to make a clarification: while in the voltage measurement the meter leads are connected between two points, however, and in parallel, measure the current meter must be in series. If you have a digital meter, move the switch on the range meter at the level they presume to be the value to be measured, being a little wide. For example, if the circuit can slide up to 500 mA, choose the range rate of 1 or 2 A or directly the 10 A. The plug of the negative probe insert it into the socket of the common (COM) and that of the positive test lead into the storage sleeve that matches the type of measurement to do in that signed A (one of the measures of low current) if you placed the selector on the

measurement of current low value , ie in the marked 10 a (or 20 A, depending on the meter you have) if the selector is on the high current flow. If you have a meter with separate bushings, bushings identified that relate to the common (negative probe) and then the range in the amperometric measurements, which allows to easily measure the current that should presume to flow through the circuit on which you are going to make the measurement. Usually the town is signed or = COM (Figure 8.15). In the measurements in continuous current, the leads must be connected in a precise manner: the positive (red) should go on the wire or terminal from which the current arrives, while the negative (black) to be pointed at the wire or terminal from where the current flows out. Make no mistake, before making the measurement of current, the tester willing to measuring DC voltages go and see what thread positive polarity, or alternatively, if you need to measure the current in an electric motor, in an electronic circuit, a timer, a bell etc., to know what is the terminal to which to connect the positive test lead traced to the positive supply line. Once this is done, unplug the wire that goes on the + and touch it with the red lead of the multimeter, with the black ferrule, tap the + user. So you are sure that the current will enter the red lead from the meter and will be released from the black one. However, if you use a digital multimeter polarity reversal should not worry more than necessary: if you put the tip down, the instrument marks - in front of the displayed value. The correct polarity should matter to you more if you use a multimeter, because in this case the hand moves to the contrary and bumps at the beginning of the scale.

Figure 8.14 Measure of DC voltage using a digital multimeter: the red tip must placed to the positive wire and black on the negative. If you reverse the position of tips, instruments gives a negative value.

Measurements of Ac current The measures alternating current are less problematic, as there being a polarity (because the current alternates its polarity) there is not even the burden of staying identify the positive and the negative of the power line. When you make a measurement in AC, you can place the leads in the case, because one or the other. But apart from this detail, for everything else you need to do as already explained with regard to the measures in DC: in the multimeter without a selector, you must identify bushings common (= or COM ) and appropriate range of measure, or the common and that of the amperometric measurements; then enter the black plug test lead into the socket joint and the red test lead into the socket of the capacity. Instead, if you have a digital multimeter or an analog rotary switch with

measuring ranges, identify the common bush and stick the plug of black lead, then enter the plug red test lead into the socket of the amperometric measurements. Note that here we are talking of black and red only for a matter of order, because, as I said, we could easily swap the plug and the positions of the probes and the measurement would be done correctly anyway. Even in the case of measures of alternating currents, identified before the one that is the range rate that can reasonably understand the value to be measured and set with the selector; clearly evaluated immediately if it is the case of using the range rate at high current (10 A) and the relative bushing. The advice is, when you have no idea what is the current that may flow into the instrument, choose the highest range, and then, if you see that the needle moves little or that the indication of the display is limited to the first digit or first two digits, choose a range with full-scale lower. This applies to the measurement of both direct or alternating . Also, remember that if you have a meter with auto range, you need only set the measurement type with the selector: choose it if the range alone.

Figure 8.15 - Measure of low intensity continuous current: The multimeter must to connected breaking a wire. Ever, positive probe must to be connected on the wire from wich current arrive and negative at the wire that carry cur

Resistance measures In addition to the voltages and currents, the multimeter can also measure the electrical resistances, although with a certain approximation (more than 5%). The measuring range ohmetric is ideal when you need to check the value of a resistor for electronics which are not seen the strips because the outside is smoked by overheating or because the theme song came on, but it is also very useful in lowest range, to ascertain the presence of any short circuits in electronic assembly. Already, the lower one is one of the most commonly used range rates of the multimeter, both because it allows you to check if there is a short circuit between two wires or tracks on a printed circuit board, is to make the evidence of continuity of the cables or to check if a transistor is shorted. In addition, always with the scope to lower the resistance tester is used to identify the wires in multiple cables: for example, if we have a 5-conductor cable all the same color and do not know what the other end, it is enough to combine on the one hand and on the other a pair of wires to touch two at the ends of the conductors to occur when the pointer of the meter or the display shows zero resistance or a few ohms. In the multimeter is usually provided in the ohmetric course, the acoustic warning function, combined with the lower range rate, when the measured resistance is below

twenty ohms and can be considered if there is continuity or short circuit, a buzzer sounds (buzzer) inserted into the instrument. But not only in the ohmetric course usually is also a very useful function dedicated to verification of junction diodes; in other words, with the same measuring circuit of the resistors, with correct polarity, can occur if a diode or the junctions of a bipolar transistor are in place. The ohmetric measures are useful to verify the integrity of the windings of an electric motor and a transformer, the voice coil of a microphone or speaker magnet, the coil of a relay or the tracks of a printed circuit, the correct functionality of switches and buttons. How to measure the resistance Perform resistance measurements is very simple: just insert the tip into the sleeve of a common (COM in digital meters and = COM or analogue) plug and that of the bushing V (DMMs) or the corresponding the desired ohmetric range, which should be chosen always starting from the maximum measurable resistance and descending gradually of lower range rates, unless already have an idea of what may be the resistance of the component to be measured. If you use an analog meter (with a needle) in the ohmetric function, the scale of the instrument is not linear : it is very large ( very spaced values ) at the beginning and it compresses ( values closer and closer together ) towards the end , which is why should always choose the lowest range permitted or that the value is expected to have the strength to try, so read it in the most expanded scale , which is more readable and clear. To measure the resistances simply apply the test leads one to a terminal ; note that the arrangement of the leads does not matter , in the sense that there is positive and negative, unless you want to check the diodes . In making the measurements, remember to never measure the resistance in the circuits where they are: in fact the components mounted in their circuits can be in parallel other components, so that the resulting resistance measured by the

www.riparazione-notebook.net Measure of resistance of a component, or the continuity of it: it makes using ohmetric ranges connecting multimeter as you can see in the picture. 162

instrument and not the result of a resistor but certainly lower. In addition, when you make ohmetric measures you must not touch the pins with your hands as this not because the voltage given by the tester may give you the shock (in this sense you are in a barrel of iron because battery gives 3 to 9 volts and however, the current that escapes the instrument so as not to damage the components under test is a few tens of microamps or some mA depending on the selected range ), but because in the measuring circuit are placed in series with the woodwind instruments (micro-ammeter or voltmeter LCD) resistors that in some loads are also quite high. Our body conducts current and has a resistance that may be worth even a few ohms, then tapping with your fingers the test leads or terminals of the resistance being measured we put our body and its resistance in parallel, thus obstructing the measure, which will be less. For the detection of short circuits and verification of electrical continuity or the identification of wires, using the lower resistance range, than in digital multimeters quality is matched to 200 ohms full scale or on their own. One proceeds exactly as for the measurement of the resistances. The same technique can be used to test a fuse, be it from home or machine by touching the tips it should be noted that resistance is zero or very few ohms if there are several ohms or infinite resistance , the fuse is blown. All the tests described here are made without regard to any order or any polarity: you can exchange the red test lead with the black without any problems. Testing Diodes The ohmetric scope around 2 kohm full-scale allow you to check the status of the diodes, and many testers have on them, the symbol of the diode just remember that possibility. Other instruments have, however, a special dial position dedicated to the diode test. In any case, whatever the range or function choice, remember that you have to control a junction the correct polarity: put the black probe jack into the socket joint or in the common measures of resistance and the red probe jack into the socket given to measures ohmetric or extent corresponding to the diode test. Once this is done, touch the red test lead to the anode of the cathode and the black (you’ll recognize it because it is the terminal that is on the side of the coloured band on the body: the instrument should indicate a resistance in the order of a few hundred ohms, but it depends on the power of diode. If the test leads are reversed (reverse bias) you will see that the resistance becomes infinite (not measurable) in the sense that in the analog meter the needle will go to zero and in the digital indication will be 1. If instrument will continue to give a measurable resistance, it means that the diode will be damaged. The same applies if the measured resistance with the red test lead on the anode is close or equal to zero. With the tester can test all the diodes typically have a threshold voltage up to just over 1 volt: hence the common silicon and germanium rectifiers, PIN, the Varicaps, the Schottky and Zener also, but only in direct polarisation. Unfortunately, with a large amount of multimeter it is not possible to test the LED’s, since their threshold voltage is typically

higher than that of the common diodes ( ranging from 1.8 to 4 volts ). However it can be found multimeters that performs this kind of test; depending on the circuit that equips instruments and depends also from the battery voltage. Test bipolar transistors Before seeing how you take advantage of this feature, it is appropriate to make a useful distinction to avoid misunderstandings, with a digital multimeter you can do two types of evidence on the bipolar transistor, ie, verifying the integrity of the joints and the extent of the gain in current (hFE). What interests us here, is only the first, as in the repair of laptops need to know if a transistor is interdict or shorted, and if not properly amplified, since virtually all of the transistors used in a computer is switched. Verifying the integrity of the junctions is substantially that described when it is spoken of the verification of the diodes; fact, since the bipolar transistors are formed by two PN junctions, each of which individually is a diode, with the multimeter arranged on the measures we can easily ohmetric verify whether the transistor is, at least from the electrical point of view, in good condition, or whether a junction has been shorted to overheating or an excess voltage that caused the breakdown between collector and emitter. To verify the integrity of the junctions is considered a junction at a time using as a reference the terminal remains in common, that is the base. In this type of test is determining the polarity of the leads, then you need to enter in the COM terminal of the spinet, negative (black) and V/ the jack of the positive (red). Figure 8.18 - With ohmetric scope it can test integrity of diodes, but also the junction of the bipolar transistors.

www.riparazione-notebook.net How to verify integrity of a fuse: if all is right, the multimeter detects zero o a few ohms, while if fuse is broken, instrument detects infinite resistance. 164

The range to be selected is the one specifically indicated, namely the one that gives the symbol of the diode. During the tests of integrity of joints , remember not to touch the terminals of the transistor or the metal of the tip with your fingers, otherwise you will get incorrect information. If the component under test is an NPN transistor, place the red test lead on the base and black at the collector, reading the indication of the instrument, the resistance should be a few hundred ohms. If the indication is of infinite resistance (1. in the display of digital multimeter), or near zero, the junction is interrupted or short-circuited, respectively;, in both cases the transistor is to be thrown away . After trying the base-collector junction , leaving the red lead on the basis move the black emitter and check the base-emitter junction , even in this case, the resistance must be of some hundreds of ohms , otherwise (infinite resistance or next to zero) it is bad. So you’ve tried the junctions in forward bias, however, should give it a try in reverse bias, to see if the joints have no particular problems. This is done by repeating the steps above, but reversing the position of the leads, so place the black on the base and the emitter now red, now on the manifold, in both cases, the tester should indicate infinite resistance. If you want to test a PNP, the tests to be done are the same as those described above for the NPN, only you need to reverse the order of leads: to the evidence brought forward bias based on the black and red on the manifold, and if the meter reads infinite resistance (1. in the display of digital multimeter, or left hand in the analog) or almost zero, respectively, the junction is interrupted or short-circuited. After testing the base-collector junction, leaving the red lead on the basis move the black emitter and check the base-emitter junction, even in this case, the resistance must be of some hundreds of ohms, otherwise (infinite resistance or next to zero) it is bad. After performing the test in forward bias to the past in reverse bias, which is the red test lead to having to go on the base; touching with black now the collector, the emitter now, you need to measure an infinite resistance or nearly so. If the resistance value is low (less than a few tens of ohms )

Figure 8.19 If diode is ok, the multimeter shows a low resistance (200÷400 ohm) when positive probe is put on the anode, while infinite resistance if positive probe are placed on the cathode. If diode is short-circuited, resistance results zero o a few ohm regardless of polarity applied in the test. If diode is interrupted, resistance

www.riparazione-notebook.net ) regardless of 165

the joints are damaged. Testing FET Figure 8.20 Test of junction of the bipolar: NPN on the left and PNP on the right; test is applied to base-collector junction and must to be repeated from base and emitter.

In the FET with gate junction can verify both the integrity of the gate, both the resistance of the channel in the first case proceed as with a diode. Let us first examine the analisis of the N-Channel JFET: for the test in forward bias to the gate goes positive and the tip on the drain or source (indifferently) the negative probe; in this case the measured resistance will have to be a few hundred ohms. A value close to zero or tends to infinity means that the junction of the gate is faulty. You can also make a reverse bias test to see if the insulation of the gate holds: reverse the order of the test leads and check that the indication of the resistance of the multimeter is practically endless. As for the P-channel JFET, the tests are similar, but changes the arrangement of the leads: in forward bias, leading the black lead on the gate and the gate or red regardless of source, the measured resistance should be a few hundred ohms values close to zero or infinity indicate that it is bad. As far as the reverse bias, the red test applied to the gate and the gate in either black or source and verify that the indicated resistance is close to infinity. Now we analize the test applied to the MOSFET, where one can verify the presence or absence of the channel without gate bias and the possible interruption or short circuit; to make test, arrange a tip on the drain terminal and one on the source (in this case, the gate does not matter) without heal polarity, unless the MOSFET does not have the protection diode. If this is so, for the N-channel

www.riparazione-notebook.net Test of a gate junction of a N-channel jFET. 166

type put the positive test lead on the drain, or do the opposite to the channel P. In enhancement mode MOSFETs, you should measure resistance (without gate bias) practically infinite; if the measured value is very low or close to zero, it means that the transistor is damaged (the chip is fused to an overload). In the depletion MOSFETs, the measured resistance varies from a few ohms to several hundred ohms: depends on the power that the component can withstand, in the sense that transistor from a few watts have a very high resistance of the channel and instead those for high powers have just a few ohms. If the measured resistance is too high, the MOSFET is damaged. In power MOSFETs, providing that serve to switch inductive loads, manufacturers often fit a protection diode between drain and source; for the tests, we can use the 2 kohm range or otherwise reserved to the diode test. You will notice that when the test leads are connected in a certain way, the tester will indicate a normal resistance of the channel: this is completely normal and should not be read as a failure. Take for example a power MOSFET to fill N-channel (type the Si4812DY, in TSSOP 4+4 pin case): applying the red lead to the source and the black to the drain, there is a resistance of a few hundred ohms, because the diode is conducting. Reverse the test leads: black with red on the source and the drain, the resistance will be infinite or almost would still be too low or zero, the MOSFET would effectively short-circuited and then thrown away. For all the MOSFET needs to consider the capacitive effect of the gate, which could cause false indications as the tester applies a certain voltage: if you touch the test leads with gate and source, the component can remain active between drain and source. To explain what, suppose you want to control a MOSFET Nchannel enhancement-type and touch the positive probe the gate and the source with the negative: under these conditions creates the channel, because the component is biased. If we now move to the positive lead on the drain, we will see the incredibly transistor conduct, even if the gate is not polarized, but in fact it is because the gate has accumulated a certain charge and for a while remains energized. To avoid feeling fault (short circuit between drain and source) a MOSFET, it is therefore important to short-circuit, before the measurement of the resistance of the channel, gate and source with a metal screwdrivers; this applies to the enhancement-mode MOSFET. For those who function in depletion-mode, the accumulation of charge on the gate can interrupt the channel and make it look the transistor interrupted, even in this case it is providential to short-circuit G and S prior to the measurement . The oscilloscope This instrument, of fundamental importance for the electronic technician, is able to read the voltages and display them on a screen sized (divided into squares), in its most basic form consists of a circuit that periodically (the frequency of reading depends on the basis of time you set) reads the voltage amplitude between a pair of test leads (probe) and displays it on a CRT or an LCD screen. Each input of the instrument, which owns a probe, is called “channel” or “track”. The oscilloscope is very important because you can see the waveforms, that is the change of variable voltages and AC, as if it were drawn on paper.

In short, an oscilloscope is a monitor CRT in which the circuit is driven by the vertical sync signal (the drawn point moves up the more so the greater becomes the amplitude of the input voltage) to be displayed and the horizontal is a common sawtooth generator that is made from a network of trigger. To follow the variation of the signal with the right speed (for example, a triangular-wave signal to 100 kHz rises more quickly than one to 10 kHz) must adapt the frequency, ie the slope of growth, of the sawtooth; this is done by adjusting the time base. The latter is defined in µs/div (microseconds per division of the screen) and the more you reduce its value, the higher the frequency generated by the oscillator and vice versa. The correct setting of the time base is essential to obtain a fair view, in fact, the higher, the more the signal is dense, while decreasing the ms/div the displayed waveform extends the width. If the signal to be displayed is periodic and has the same frequency of the oscillator sawtooth, on the screen is exactly one period, if its frequency increases, at constant frequency of the sawtooth horizontal deflection of the screen will contain more than one period, while the frequency decreases if the screen can not display the entire period. If the input signal is applied at any moment, even if the frequency is greater than the sawtooth is not said that it appears neatly on the screen, as can low shifted with respect to the top of the scale. For example, having a signal of the same frequency can be to appear from mid-amplitude until the middle of next period. To make sure that the oscilloscope to display the waveforms from the leftmost side, using a circuit said Trigger: it is a variable threshold comparator (the knob is adjusted precisely with the call trigger) that engages a certain signal level (the lowest setting the threshold, the more in the view to the left is the level of zero volt waveform…) to display and starts the sawtooth precisely the occur

Figure 8.22 - In a Nchannel depletion-mode MOSFET, appling positive probe to source (right) it must detect the presence of protection diode; with the ame probe on the drain (left picture) resistance must to be infinite, otherwise

168 www.riparazione-notebook.netcomponent is bad. rence of that level. The trigger can be coupled to one of the channels of the oscilloscope , or both, or may be synchronised with an external source (EXT ), which serves for particular measures, or to obtain a correct visualization when using a function generator provided with output trigger synchronised with the signal it produces. The other fundamental adjustment of the oscilloscope is the width, measured in V/div (volts per division screen): operates on the gain of an amplifier or attenuator on a place between the probe (input of the corresponding channel ) and the amplifier that controls the vertical sync . The adjustment is one for each of the channels of which the instrument is provided. Choose the oscilloscope In choosing an oscilloscope must first consider their needs and assess what types of signals you want to display or, more exactly, it must be said that the CPU clock , multiplied internally , however , is very high and a few oscilloscopes are able to go to the base frequencies. In principle, a 100 or 200 MHz is fine. Then there is the discourse of memory : it is better to have an oscilloscope with memory because it allows you to stop some images and analyze certain signals. Let’s see the main parameters of an oscilloscope. Number of Channels

Most oscilloscopes with 2 or 4 channels, however, are commercially instruments for mixed-signal (called MSO - Mixed Signal Oscilloscope) where the analog channels are joined by other 8 or 16 channels can acquire digital signals only, but with the ability to set trigger and execute coordinated measures. In essence, it is like to have an oscilloscope and logic analyzer integrated in the same instrument. Screen

While in analog oscilloscopes display quality depends on the characteristics of CRT, digital ones in one of the key factors that influence the quality of vision is the update frequency (refresh rate) which is the speed with which the oscilloscope is capable of acquire and update the display of the waveform. A faster update equates to a higher probability of capture, and then display on the screen, infrequent events such as the “glitch”. In choosing your oscilloscope, you need to pay attention that in some cases the highest refresh rate is only valid when they are not activated special functions, such as advanced triggers or extended memory depth. The first generations of digital oscilloscope were slow in the view, compared to analog oscilloscopes. Today things are better, the more so the greater the available memory.

Figure 8.23 A typical digital oscilloscope and showcased the main commands it can find on the control Bandwidth

The bandwidth, expressed in MHz, is the reference characteristic of each oscilloscope and should be chosen according to the maximum frequency of the signals to be checked, or the steepness of the edges of the signals of which one wants to measure the rise or fall time (short rates require a high frequency). In principle, the bandwidth of the oscilloscope must be 1/2 of the rise time, so if this time is 0.01 ms, the bandwidth must be at least 20 MHz. If the oscilloscope is digital, its sampling frequency must be at least 4 times the bandwidth of the oscilloscope and the highest frequency of the signal to be measured. The sampling frequency is another key feature of the digital oscilloscope and is expressed in samples per second (s/s) or it’s multiple; in evaluating a instrument should be noted that sometimes the manufacturer claims the maximum sampling frequency and in this case is important to check under what conditions is reported. Indeed in many oscilloscopes is exploited to increase the sampling interlaced maximum sampling frequency , and this is at the expense of the number of channels can be used simultaneously. For example, a 4-channel oscilloscope could operate at maximum sample rate with only one or two channels, but if you want to use all channels have to settle for lower sample rates , often referred to only in small or in the notes of the technical specifications of the instrument. To evaluate the sampling frequency ( fc ) of which is needed is to determine the temporal resolution (rt) between the desired points of acquisition, that is: fc=1/rt. For example, the sampling frequency which allows to observe the points in time with a resolution of 1 ns is equal to 1/(1 ns), or 1 Gs/s. Digital oscilloscope, also the memory depth is closely related to the sampling frequency; with slow settings of the time base, the maximum sampling rate is reduced enough that does not end the acquisition memory of the instrument. When the A/D converter converts the analog oscilloscope in numerical form, the results are viavia stored within the memory of high-speed acquisition of the oscilloscope, so the depth of memory required depends both on how long it is the interval of time that you want to observe, both by how frequent you want it sampling. If you want to observe long periods of time with high temporal resolution, then you need an oscilloscope with a large amount of memory. Typically the depth of memory (Pm) required is related to the sampling frequency and the

period of time (t) to be observed, by the relation: Pm=fc x t. In particular , some models when they use all the memory of the acquisition are forced to slow down other operations, for example the display speed. Trigger

The trigger is usually synchronised with the rise or fall edge (edge trigger) of the signal to be displayed, however, to make measurements on systems that use serial buses can be very convenient to have a trigger based on specific conditions that occur on the bus as SPI, CAN, USB, I ² C, FlexRay, LIN or others. For troubleshooting and intermittent faults another useful function is the Glitch trigger, available in various forms in many instruments of the medium-high. Finally, many modern oscilloscopes offer specific functionality trigger for video applications such as TV and HDTV, also useful in the analysis of signals from notebook equipped with HDTV and HDMI output. Probes

The probe (Figura 8.24) determines the overall bandwidth of the measurement system becomes an integral part of the circuit under test by changing the behaviour, for which impedance and bandwidth of the probe should always be taken into account, especially when measuring signals high frequency. In general, the active probes not only have a higher bandwidth to the passive probes, but they are also able to mitigate the effects on the circuit under test. The probes for oscilloscopes can be direct or dividers, with typical division factor of 10 (x10 probe), some instruments provide a selector that allows you to adjust the scale volt/div. to the probe features. The direct probe is no more than a coaxial cable terminating in a tip , while the geared down internally has a resistive divider in parallel with the capacitors, one of which is variable: it is a com

www.riparazione-notebook.net Probe for oscilloscope equpped with springed tip needed to engage to test points or components of the circuits. 171

pensator adjustable with a screwdriver in order to alter the less possible signal; adjustment is accomplished by bringing the tip into the calibration signal of the instrument , and then acting on the compensator up to make the fronts of the rectangular waveform displayed on the screen the more straight as possible. The compensator has the purpose to adapt the impedance of the probe to the oscilloscope input. Interfaces

Most modern oscilloscope has at least one common interfaces used to connect a PC, such as ethernet or USB , which greatly facilitates the exchange of data and any remote or automatic control of the instrument. Some models, such as those compliant to LXI , contain within them a Web Server, which allows you to manage them from your computer with a simple Internet browser via LAN or remotely via the web. Use the oscilloscope Let us now see two notes on using the oscilloscope, with the premise that, as this is not a book dedicated to this instrument, we will limit ourselves to a few cases. To view a signal must first connect a probe to a channel, then the channel selector to choose to display that channel, then connect the clip end of the probe to the circuit ground and where to make the measurement with the tip touching the point in question; if know the voltages in the set volts/div. so that the voltage is in the height of the screen, or from the rest position of the track at the top of the screen in the case of negative voltage or from it to the bottom, in the case of negative magnitude. If the voltage is alternating, to display all necessary to choose an amplitude for division such that the screen contains the waveform. Remember that the volt/div. indicate how many volts corresponds to a picture of the screen using a direct probe (x1), if you use a x10 probe (with divider that divides the voltage by 10) you have to remember that each picture is worth 10 times the value indicated by the selector volt/div. Before making any measurement, regardless of the amplitude make sure that in the point to measure the voltage does not exceed the maximum tolerable by the oscilloscope: in fact, if the amplitude exceeds the displayable nothing happens and to retract the waveform the screen just play it on the knob volt/div. or choose a x10 probe, while if it exceeds the maximum acceptable voltage input, the oscilloscope fails. Using the x10 probe the maximum voltage to be multiplied by 10, in the sense that if the instrument accepts as input a maximum of 50 Vdc, the probe can touch points where you can reach up to 500 Vdc, and this in theory, because in practice the capacitors in the x10 probe could let pass short high voltage pulses. For notebooks the only areas of concern are the inverter output to the LCD and the input stage of the AC/DC external . If you do not know the frequency of the signal is necessary to start from the lowest value of the time base, or set the minimum time per division, then go back until the signal is not displayed correctly, remember that each picture is worth a period equal to the set on the basis of time, then choosing 1 ms/div. if the signal has a period equal to two squares means that it is at a frequency of 500 Hz. With a two-channel oscilloscope or more, you can view multiple signals simultaneously: just set the switch to CH1+CH2 (or CH1+CH2+CH3+CH4 for the

four-channel oscilloscopes), you can also toggle (switch position ALT) tracks, or machinery out its sum. The latter function (ADD) is mainly used when you want to see the result of two mixed signals and in any case in the verification of notebooks typically not needed. To be able to properly display the waveforms, you must assign the trigger generator (using the appropriate selector) to the corresponding channel, or, if you use more than one channel, the first one.

The logic analyzer It is a digital laboratory able to sample and reproduce on their screen logic states detected by a sensor at any point in a circuit, it is very useful because it allows you to monitor the progress of signals such as clock, data, addressing memories, dialogue on buses such as USB and I²C. To choose a logic analyzer is necessary to take into account the system of probes, to capture, display and analysis capabilities. Measurements made with a logic analyzer are as accurate and reliable as it is its system of sensors, the choice of the probe system should not be neglected the opportunity to have some flying probe (flying probe). Let’s look in detail what are the most important features of the logic analyzer probes: a probe low capacitive loading reduces the interference on the circuit under test, which can function in a realistic way and allow the logic analyzer to represent correctly what is going on, and this is particularly true because the higher the frequency of the signals to be monitored. If possible, it is best to use probes that do not require adapters between them and the circuit under test, since each additional adapter and a load becomes another point of potential failure of the measuring chain. If the probe has a bandwidth less than that of the analyzer , limits the useful bandwidth, therefore it is better to choose probes with bandwidth at least equal to that of the acquisition system of the logic analyzer itself. The logic analyzer can operate in two distinct modes of sampling: in the time domain (time analysis) and in the domain of the states (state analysis). The two modes have different purposes and principles of operation and complementary to each other: when you need to monitor the temporal relationships between various signals over long periods of time even using the temporal analysis and visualization using the typical waveforms; instead if you want to control sequences of events, it is useful to the analysis of state, often associated with views of tabular or listing. Some logic analyzers can run simultaneously in the two capture modes, allowing you to see more correlations in the behaviour of the system under test. The number of channels depends on how many signals must be displayed simultaneously: for example, having to monitor a line SPI should have at least three channels, along with the clock to see if the data travels to and from the master unit. It should be noted that for some instruments, only a limited number of channels can operate at the maximum speed of acquisition, while the additional channels can operate at a lower speed. The latest generation of processors already require 100/150 channels if you want to cover all of the I/O devices, however it comes to conditions that rarely make sense in the repair of laptops, because a thorough search of problems on the data bus in communication with a memory or a GPU imposes the times that are not always eligible, given that the repair

would cost an working , almost like the PC. In the acquisition mode in the time domain, the logic analyzer works as an oscilloscope and stores the samples of the acquired signals in its memory asynchronously with respect to the clock signal of the test system; therefore, the higher the sampling frequency, the higher the resolution of the captured measurements. It goes without saying that in a high-speed acquisition, must match a memory capacity equally high to be able to accumulate a significant number of samples in the time domain. The amount of memory in your logic analyzer determines how long you can see the system in question without losing significant information . The minimum amount of memory that must be obtained by multiplying the period of time to monitor for the sampling frequency or the frequency of the external clock. The availability of a large amount of memory increases the probability of being able to capture of rare events or the correlation between cause and effect which are sometimes separated considerably in time. As for the display, it must be said that a wider screen allows you to see , when necessary, multiple channels simultaneously or in an orderly fashion to show the additional information that serve to bring a measure into more intelligible in its context. Another trick to show more information simultaneously available in some logic analyzers is the dual-screen mode, which allows you to connect an extra monitor or other display where channels, or additional information about

www.riparazione-notebook.net A typical logic state 174

the channels displayed in the primary display. Finally, one must not forget the possibility to connect the instrument directly to the PC, where there may be a screen or earpiece with superior characteristics of the instrument.

Disassembly the notebook Well, explained the instruments of the laboratory can analyze the first step regarding the repair of laptops: disassembly. Although it may seem trivial , disassemble a laptop until you get to remove some of its internal components can not be an easy task, since in some cases the screws and joints are deliberately hidden by the designers, partly for aesthetic reasons, but above all to deter technical undertaking and push customers to call technical support of the OEMs. If we talk about dismantling must be distinguished depending on what you intend to remove: optical disk drives and floppy-disk you extract almost always means the release levers or screws accessible from the bottom of the base of the computer, but are sometimes blocked by an internal screw which accessed by removing the keyboard or, worse, by removing the upper part of the base. RAM and wireless modules are almost always accessible doors screw at the bottom of the base of the computer and the same applies to the hard-disk. Instead the rest and the mainboard can be achieved only by removing the upper part of the base or the entire base; for rest means any memory modules internal, separate video machines (even if there are notebook in which the video machined is detached from one door bottom of the base of the computer) modules modem. Even for the monitor is necessary to remove the shell, since the display, the backlight and its controller (typically the inverter that powers the CCFL bulbs) are inside. In these cases, you should identify the screws, remembering that some are under rubber stoppers and sometimes masked by labels, or be placed in the battery compartment, which is then removed. The screws to detach the keyboard are usually denoted by the symbol of the keyboard, while those to disassemble the upper part of the base are all other, or are marked with a triangle. In some notebook, to simplify the replacement are written next to the screws measures (eg M2, 5x15 ) . Almost always, the removal order is as follows: 1. the screws are removed the keyboard and the other on the bottom, then the keyboard is removed, if possible, otherwise you have to remove the plaque in the upper part of the keyboard, which is often stopped by tabs or screws accessible from the bottom of the computer; 2. disassembling the upper part of the body of the computer, if you can do it, or before you remove the elements that block it; 3. disassembling the monitor by turning the screws of its hinges. These are one or two per hinge and can be accessed by plaque above the keyboard, but almost always also have a notebook or two screws on each hinge, screw from the back of the two parts of the basic shell components. To remove the need to disconnect the video cable or the video signal cables and power of the backlight and the LCD panel and in

notebooks equipped with a microphone, web-cam and wireless antenna in the screen, you must also disconnect its cables. Sometimes to pull the base of the housing of the PC you need to free the stud bolts of the connectors of the serial and/or parallel, SCSI, or any of the connectors that have the threaded columns. Often the base cover of the computer is very thin plastic and therefore fragile or easily deformable, then separate it from the base to access the interior needs a lot of forethought, the ideal is , after making sure that you have removed all the screws that bind (beware that in some PCs the lid is kept by the columns that attach the modem or the wireless, so you have to remove the latter and columns) wedge into the seam a sheet of rigid plastic or a screwdriver with a wide blade and thin, then do lever to detach the two components of the base. As you grow a part, you have to move around the perimeter until you open the base. In place of screwdrivers or foil you can use a plastic spatula or, better still, a plectrum hard as those used to play the guitar: it is a solution unorthodox but it works great. Open the notebook, if you have to remove the motherboard, the first thing to do is try to remove the screws, and these usually are marked by triangles screen printed on the surface. Sometimes you may also need to remove the cooling fan (for example as in some HP Pavilion DV9000). Note that in certain notebook the mainboard is screwed on the back of the lower part of the base through the hexagonal columns (or the other shape) of the connector for the external monitor or that of the serial or parallel port, in this case, it is not possible to remove the motherboard before undoing these columns. Before removing any notebook, especially those with polymachinebonate container and then polished, it is good to rest on the work surface sottotovaglia a cloth or rubber, or just one of those sheets of foam material that are used in

www.riparazione-notebook.net Disassembly of notebooks’s base: it starts unscrewing the screws on the bottom that allow you to release the top of the shell. 176

the packaging of monitors, notebooks and motherboards, to avoid scratching the shell of the computer during the various movements required by removing the screws, when the notebook lid to operate rests on the bottom. Release the connectors The modedrni notebooks have connections between the various parts and machineds, but also between tabs and keyboard, media buttons, video modules , made with flat-cable very delicate, made from strips of plastic deposited with the electrolytic copper conductors, for this. Therefore, the cables should be disconnected with a lot of attention and the same goes for the connectors. These can be of various types, but those for the flat are the most delicate and require special machine, so as not to break them. The connectors can be: plug- in pressure; plug with lock; to support with swivel stop . The former have a slot where you can find the electrical contacts and the flat is introduced in them keeping it squarely on the end (which is usually reinforced to not flex ), and pushing hard, the extraction of the flat cables is accomplished by simply pulling, because there is nothing that holds if the pressure of contacts. To know the correct direction of insertion should be remembered as they were when they were extracted, or look inside with a light to see where the contacts , then place the flat with the tracks that way. Plug-in connectors with locking have the flat that slips into a slot and , when it comes to bottom, stops pushing in the same direction of the frame retainer until you hear it click, usually these connectors have the body white or ivory and the latch is black or brown. If you need to extract a flat by this type of connector does not pull, first with two small blade screwdrivers pull the end of the latch until it snaps. Try not to do too much force, otherwise you can rip the latch. To orient the flat compared to the contacts of the connector same as for connecting to pressure. Finally, the connector has to support contacts lying flat on the bottom and you are resting, then pressed by the firm, which this time is rotatable about a fulcrum. To extract and disconnect a cable in this type of connection must lift the latch and rotate in the opposite direction using a small hunting blade screws. To replace the flat, after having supported the side of the tracks on the contacts of the connector, turn lock face down and then push it to the bottom by snapping and locking it. This type of connector has the body white or ivory and the still black or brown. Spray for laboratory Repairs may be useful in some spray designed for virtually the electronics laboratory, the most used are:

Figure 8.27 Detach of flat-cable from it connector provided of a rotary latch: from left to right, it can see closed connector, lift of the latch ad removing of the flat-cable.

freon; isopropyl alcohol; instant ice; air jet. The first is a solvent flux and is also found in liquid form, was once used to clean circuit boards solder wave, but now for ecological reasons (it is considered mainly responsible for the ozone hole in the atmosphere) has been replaced isopropyl alcohol . The latter is more or less the same thing and is used to clean up the welds or by desoldering flux and fouling). In its place, you can use “homely” solvents as the AVIO (is a very volatile) or trichlorethylene, but it must be used with caution because it can melt certain plastics. The instant ice is instead a stream of humidified air or compressed gas refrigerant coming out of the bottle expands and the sharp drop in pressure does it freeze up is used for instant cooling of the components that you suspect are dead , as the sudden cooling causes deformations and thus if the integrated contacts has disconnected to the own internal or lesions in the chip , the problem manifests itself immediately (for example, the CPU and the memories stops the computer). The air jet is pure compressed air in cans, which is used both to cool modestly without subjecting to thermal shock typical of instant ice , both to blow away dust and foreign bodies from the electronic boards. It is used often to clean keyboards and the inside of the trackball. Looking for spare parts When the notebook repair requires the replacement of non-standard components, ie not merely transistors, fuses, integrated circuits and the like, need to get spare parts , which are for example the RAM or a compatible keyboard or internal machineds. To order it is important to identify the code (part number) which is normally reported together with the barcode label of different shapes applied to the component. The code is the very important since, especially for motherboards, sometimes it can happen that not just order them indicating make and model of your laptop and in some cases even the serial number (production serial number of the PC) can be useful: in fact, some homes change suddenly motherboard within the same year of production, because they cater to a new dealer, then it may happen that by ordering the parts with model and year of production we see get the wrong one.

To contribute to this inaccuracy sometimes eronee directions of the manufacturers that communicate distinct components derived wrong or do not communicate at all, at least to retailers of unauthorized parts.

CHAPTER 9 FAULTS ON POWER SUPPLY It is time to approach to research and problem solving in notebook computers, then you do so starting with faults related to power supply, which may be responsible for many and varied difficulties or who come to also cause misfire portable. The fault must be sought by examining the behavior of the PC, however, to believe it is not enough to compromise the power supply to see if the computer is turned on or not: the examination must be deeper and must relate to the internal circuit, or the motherboard. Before examining the typical behavior that might be suspect a power problem, it should be noted that for input means a whole chain of devices: the AC/DC external to the computer, the connections (or the plug of the AC/DC and plug of the notebook’s power ) inside the main power supply and all other stages of power on the motherboard. If your computer while powered on, pressing the power button shows no signs of life (ie not turn on any light and does not feel movement or activity of the hard drives or optical disc player) the first thing to do is make sure that the network adapter functions and to deliver the expected voltage and the value of the latter is inferred from the label shown on one side of the feeder. It is therefore necessary to arm yourself with multimeter, set it on the measurement of voltages with full scale of at least 20 to 30 V (for auto-range multimeters there is no scale to be set) then tap each with an electrode tip of the plug of the power supply; the case of an AC/DC adapter which provides more tension, you must take your negative probe on the ground contact and the positive impact on internal connectors that carry various voltages. If the power supply voltage or does not provide measurable value to its plug is at least 30% lower than it should, replace the power supply, but if the voltage is ok , it is not said that the power supply has problems: for example might not hold the cue, or fail to deliver the rated current ( the value of this can be found in the usual plate) required by the notebook and that according to the nameplate data should provide. To check this you just get a power resistor (wire) whose resistance value is determined by dividing the nominal voltage for the power supply on the rating plate: for example, if we have a voltage of 18 V and a current of 4,5 A, the resistance must be from: R = 18 V / 4.5 A = 4 ohms The power that this resistor will dissipate amounts to: P = V x I = 18 V x 4.5 A = 81 W Given that the market can not be found resistors that power, you should build the tests required by placing resistors in series 4 wire to 1 ohm, 21 W. The resistor should be connected with two wires to the power supply and plug with a tester , check that the voltage under load is not significantly different ( 10% is acceptable but less than…) from that measured without connecting the resistance. Otherwise it means that the AC / DC has some difficulties to provide the required current and therefore must be replaced. You can also groped the repair supply from the network, but this requires much attention because a part of it is fed from the mains voltage; typically the AC/DC consists of a rectifier formed by one or more diodes and an electrolytic capacitor, which transforms the alternating voltage in a constant whose value is about 1.4 times greater than that RMS value of alternating voltage, so in the case of the Italian main network are obtained 1.4x220V=308V and for U.S.A. main network 1,4x110V=154V.

By now all the AC/DC are universal, in the sense that adapt to mains voltages between 100 and 240 VAC, so there are no switches in the rectifier. The high DC voltage obtained feeds a DC/DC managed by an integrated circuit and fed back so as to maintain the output voltage to the value required, regardless of what is the voltage at the input (provided that this is maintained in the field provided); the integrated pilot one or more power MOSFETs, recognizable because they are leaning to heatsinks variously shaped (Ushaped, flat or radially). To the heat sink are also applied to the rectifier diodes, which are typically in a TO-220 case and can be single (only two terminals) or double with common cathode (three terminals of which the central is the cathode and the exterior are the anodes). In addition to these components, in the AC/DC is the transformer that converts the pulses determined by the switching of the MOSFET from high to low voltage (galvanically island and especially the network from the notebook) and typically an optocoupler which forms the feedback network, because recedes to the integrated control a voltage proportional to that output. Do not miss the fuse located on the network to protect against short circuits and overloads. The output stage is protected from excess load by means of a dynamic protection or Poliswitch. The faults of the AC/DC power must be sought first of all the fuses, then the switching MOSFET, which are the components most susceptible, in the alternative would also fail the integrated control and more rarely the feedback optocoupler or transformer.

AC/DC adapter and it’s typical plug connector; sticker on the back shows, further model and year of construction, some data like voltage and current furnished, but but also the maximum power and

Look for faults in the notebook If the AC/DC is working properly, we must begin to investigate into the notebook from a test that is used to process of elimination: we need to check if your computer turns on the battery and the power supply not and if so , the problem is feeder. Conversely, if the notebook does not turn on even with the battery, there is obviously one of the internal power supplies (such as DC/DC that powers the chipset ) does not work correctly, to resolve the doubt the test shall be made with a battery charged, possibly loaded in a computer or similar auxiliary battery charger for notebooks. This is because the computer might not even powering up with the battery because the latter is discharged due to a failure of the main power/battery inside the notebook, then in such a case the problem would not be in the stadium or in the internal power chipset but feeder. So, if your PC starts with a charged battery there is a fault in the main power supply, while charging the

battery if it does not start, something is wrong with the chipset or in internal (secondary) DC/DC who supplyes RAM, CPU and other circuits. In such a case we must start from the power input connector and follow the line to first check the continuity, this operation is carried out with the multimeter willing to measuring the resistance with very low flow rates or with the horn. It is clear that in the absence of detailed wiring diagrams you have a little ‘ go to the eye and in any case you should try to visually follow the path of the tracks that start from the power plug, if there are fuses, you have to test them with the solid flow ohmic, and found that are not interrupted (if the fuse is good the measure must be roughly the same as joining the multimeter). We must also make a visual inspection of the motherboard of your laptop and look for any components that appear burned or overheated , warped , cracked , with signs of swelling. Checked the fuses, if these are in place and power is supplied until the power supply charger, before you go hunting for faults in the other DC/DC must make sure that the main power supply or battery charger on the notebook is in place, this stage is head to an integrated circuit (eg MAX1908, MAX1987, MAX8724 , BQ24721 , BQ24702 , or ISL6251, ISL6265 ) usually placed near the battery connector. If the power supply fails, typically the battery will not charge and the computer does not work with either the power supply or the battery, why not charging (with a charged battery part could work). Another problem that can occur is that the main power supply fails to start or work on a completely different frequency than you expect, or, again, it goes immediately off (shutdown) because the overload protection acts or because the integrated circuit that governs it is defective, in which case the fault -often manifests itself after pressing the power button with a blink- and slow rhythmic power LED, but it can be diagnosed with certainty by analyzing more with an oscilloscope, the waveform on the MOSFET ( just go to the drain) of the power stage, or on the side of the inductance of the DC/DC MOSFET connected to the same, or, again, the gate thereof or on the pins of the control MOSFET localizable in the controller IC by looking on the data-sheet. For example, in the case of the MAX1908, MAX8724 and MAX8725, the MOSFET (N-channel) are controlled by the pin DHI and DLO , which in the version in Thin QFN case, are respectively 25 and 21. By analyzing the signals on these pins or the drain of the MOSFET, you see a wave of type “burst” that is formed by highfrequency periods with pauses, with a periodicity relatively slow and correlated with the flashing power LED. At times the repetition frequency of the wave periods is higher or lower and in some cases the power LED is seen even ignite. If the DC/DC main runs smoothly but at a wrong frequency, it is known not only because the notebook does not turn on, and with it the power light, but

www.riparazione-notebook.net A DC/DC converter stage on the mainboard: it is a battery charger based on the MAX8724 IC. 184

also because the waveforms detected on the above points is the frequency significantly lower (eg 500 Hz) than typical inferred from the data-sheet of the integrated controller. All of these conditions indicate that should groped to replace the integrated controller of the DC/DC charger, because even if it were a fault in the chipset or the thermal sensor to lock the power of the notebook, the connector for the battery would be measured, however, a certain voltage. Usually a fault in the charger does not provide voltage to the battery or otherwise applied voltage random passing through biasing resistors or diodes. In case you doubt that one of the MOSFET that perform switching in the switching is faulty, desolder it and check it with the usual multimeter, placing the probes between D and S, and making sure that it is not shorted, the analysis of active electronic components (diodes and transistors) is explained in detail in Chapter 8, which speaks of the use of the tester. If you connect the power supply you see the light go off, or failing that there is a strong spark, the power supply is shorted, and the fault is almost certainly in the early components: it can happen, for example, that the MOSFET power supply main are both skipped and put in short circuit the power, or which is skipped one of the protections placed in parallel to the power supply; often protection is a diode connected in a way that is normally forbidden, ie with the cathode on the positive line and the anode of the negative. This diode can fail and go short for example, too high a voltage applied from the AC/DC adapter, or if you use to power your notebook, an AC/DC that has the connections of the connector upside than as intended; in this eventuality polarity reversal is going to run the diode and two situations may happen. If your handset has a fuse in series with the power connector, this will stop (if it is resettable, PolySwitch type, greatly increases its resistance and then it cools back to lead , repeating this cycle until you power off) and the diode is saved. Otherwise, where the AC/DC is able to deliver more of the direct current that the diode can bear, the junction of this melts and shorts out, shorting the power supply. In the case of the overvoltage, the diode fails because its junction does not hold the potential difference and triggers the reverse conduction to avalanche effect, which in a short time overheats and melts the junction, as already said, with the same consequences. When these problems occur , the diode heats up to the point of burning: thus appears charred or just cracked, but not always the case , as at times the fusion junction does not reach temperatures which show unmistakable signs on the case. In this case, however rare, you must go to check with the meter set on continuity tests (flow low-resistance ohmic or audible alert) that the diode is not shorted, if you suspect that it is, you have to unsolder the diode (with the soldering iron, or, if it is in SMD, better with the jet of hot air) and try it alone or with at least one electrode disconnected from the circuit. In normal conditions, bringing the red lead (positive) on the cathode (the contact near the band marked on the body of the diode) and the black on the anode, the diode should have infinite resistance, or almost zero, or if it has a few tens of ohms or otherwise about the resistance measured between positive and negative power input connector, means that it is faulty and should be replaced.

If visual examination nothing appears, you must first find the source of the circuit , proceeding in steps: first we need to identify the location of the voltage, fuses or disconnecting power resistors that are on the main power line. In this regard it should be said that usually the switching power supplies of a notebook are all powered by a common line, sometimes protected by fuses or self-restoring common, but often free (direct) which means that an overvoltage may spoil them all together. In this case, the repair may be too expensive because it would require going to analyze all the MOSFET incorporated in the stadiums. Moreover it would be difficult to look for the fault as it should separate the various sections and this is not always possible, given that the common line that feeds passes in tracks which are also found in the inner layers of the printed circuit of the computer and which is therefore not can stop for isolating DC/DC. One thing to note is that if a short circuit occurs downstream of the power supply charger, or in the chipset or one of DC / DC converter inside , usually when the battery is charged jumps the fuse that protects it , or you burn resistance protection in series with it; evaluate this clue can be a good start to rule out any other problems.

Faults in the power plug In the notebook when the AC/DC adapter connects via a plug socket soldered to the printed circuit mainboard, it may happen that due to overheating or bad contacts, or simply because who enters and extracts the plug does abruptly or flex the (but also for a fall or a collision) welding of one or more of the same plug is less to their functions ; overheating may be caused by incorrect design (eg from an underestimation of the currents in the game), and is caused by the fact that the current flows in a section is too small and heat welding, metallic contact hole where the plug is welded or one or more plots of the plug itself.

www.riparazione-notebook.net Figure 9.3 Power supply plug soldered on the mainboard. 186

Such problems can become quite serious, because they go from simple generalized lack of supply in the PC, to the burning of parts of the printed mainboard that can cause short circuits and irreparable damage. In the case of simple detachment of the solder due to cold welding (lack of adherence of part of the weld) the problem is identified because pointing the tester probes on the positive and negative contacts of the plug which are connected to the printed circuit voltage is detected, but by connecting the positive (while the negative is in mass) over, for example on the first track that follows the contacts, not found anything. In this case it is quite clear that we must resolder the plug , possibly after cleaning the contacts and have laid flux on them to facilitate the shedding even in the solder plated holes that will eventually host them. The disconnection of welding can also be found by disconnecting the power adapter and AC/DC, with the tester willing to measures ohmetric (very low resistance) and check the continuity between the positive of the plug and the corresponding track, so as to verify the track the negative (ground). It can also happen that by measuring the voltage on the contacts of the plug soldered to the mainboard does not read virtually voltage, but this is not due to the plug, in which case there is a short circuit (this is apparent by making a test with the tester , or -in the power supply AC/DC with LED indicator- by flashing of the latter) or the power supply fails to provide current under load, while presenting live alone, on the plug. In such case, what I said a few paragraphs back. Procedure for replacing the plug In this case and where the plug is physically damaged (eg by a forcing in the insertion or extraction of the plug or by a collision) must remove the connector and replace it with a new one suitable; replacement is carried unsoldering the component with help of desoldering/tin suck pump and desoldering braid, since almost always it is a component mounting hole (THT) or with terminals that enter holes in the printed circuit , almost always passersby. To facilitate the extraction may be necessary to lift the body of the plug while you heat up the corresponding plots, in which case care should be taken not to force too much, because when the vetronite which is the printed circuit board is very hot, it can deform or tear easily and hopelessly. Extract the connector, you must wipe the good pitches with the desoldering braid and insert the new plug , then solder it stagnarlo carefully and thoroughly. Complete the welding circuit and allowed to stand for about a minute, you can clean the area of the tracks from the flux, with isopropyl alcohol spray (or with the thinner or solvent Avio) and then with a small brush. With some computer work is very easy, since the power plug is not mounted on the PCB, but is supplied already wired with its own multi-conductor cable and

(female power jack).

Figure 9.4 Various kind of power supply plug

a special connector to be inserted into the corresponding printed circuit board (Figure 9.5). In this case, we should not do damage to the circuit board, but just disconnect the connector and release sweet the plug from any retainer plate that holds it. Problems with the tracks Sometimes it may happen that the connector, moving, let make a bad contact to it pins: if at best you lose electrical continuity at worst the bad contact, causing an increase in electrical resistance between the plug and the tracks of the PCB, results in a greater power dissipation in the contact, which results in overheating of the affected areas, to a certain time, the heat can be such as to carbonize the vetronite which constitutes the printed circuit and damage, losing insulation. This implies an increase of the current and shortcircuit between tracks and contacts, so if the pitch of the positive plug is surrounded by a ground plane or the track of positive overlapped the mass in the overheated, originates a short circuit. A similar fault is insidious because it is not easy to determine: the computer’s power is too short disconnecting most of the components of the power sup

www.riparazione-notebook.net Power supply plug equpped with cable and connetctor to insertion in mainboard: this kind of plug is replace-friendly because it can replace without desoldering. 188

plies DC/DC and the fuse or protection resistor in series with the first of them. For the repair should go to attempts , starting to disconnect the components in parallel to (for example filter capacitors) and the fuse or the first coil of the EMI filter, if the short circuit there is also later, means that the mainboard has a fault on one of the feeders, while otherwise occurred a short circuit between the slopes of two layers of the printed, in the vicinity of the plug, as a result of a burn due to overheating. Power a notebook without plug Sometimes you need to try a laptop and do not have the AC/DC with suitable plug (it also happens with the universal), or of being the only suitable power supply failure, in this eventuality, you can still check if the computer works . Simply solder the two cables on the pitches of the contacts of the plug on the mainboard, after identifying positive and negative: the red goes to the positive and the black on the negative. Usually the + and - of the plug are located with the tester, placed on ohmetric range with very low resistance (continuity) Recalling that the internal contact now by convention is positive and the outer (or external ones) the negative. Touching the electrode tip with an inner strength that gives you try to almost nothing (a few ohms): this is the positive, then you touch the external contact and goes in search of the electrode which is short (or very low resistance ) with it, which will be negative. Soldered the two wires , if you have a laboratory power supply ( capable of delivering 14 to 20 VDC and a current of at least 4 A) the red will be connected to the positive terminal and the black to the negative , but if you have a power supply with plug standard coaxial with hole , insert the red wire into the hole and wrap the end of the black metal around the outside of the plug itself. Either way , if the notebook is in place should be on.

Failure of the temperature sensor and fan Sometimes it may happen that the notebook, while properly powered, does not turn on, despite the contacts of the plug into the mainboard there is no voltage; the defect could be due to a problem with the chipset (cold welding that needs reflow or failure of the chip real , then replacement is required) or by a fault in the temperature sensor, because the latter usually interacts with the chipset and can block its activity. For example, if the sensor detects a temperature above or communicates the maximum permissible threshold, the chipset blocks the power supply and does not turn on the computer. In this case, however, it should be provided to turn the cooling fan without interruption. Another question has to do with the fans, and that can still lead to shut down a few seconds after switching on, in which case it is easy to think of a problem to the mains, but it would fall into error. If the notebook heats up a lot, turns itself off while you are working or shortly after (a handful of seconds) it turns on, check the cooling fan because it probably runs too slow

(due to accumulation of dirt that hinders rotation ) or does not rotate at all. Even abnormal noises originated from the fan should be a warning that something is wrong. As mentioned, if the fan does not cool properly usually the thermal sensor shuts down the PC, but sometimes surgery is late or only above a certain temperature threshold: while CPU, chipset and GPU work in conditions of extreme temperature and long run damage or break off some of their welds, making it necessary to reflow. The fan should be cleaned with a jet of air or, if running slow or does not run because the bush on which turns the rotor is seize up , must be checked and if replaced with a new one. Very important is also regularly check that the air outlet grilles that the fans pull out a notebook or copper fins on the heat sink cooled by the fan has not accumulated lint caused by dust, soot, or other form of densification, which would hinder the removal of heat, in which case you have to disassemble the notebook until you enter the heat sink, remove the latter and blow a jet of compressed air to clean it , and reassemble it in its place and close the computer. The accumulation of dirt on the louvers (both inlet of the intake air from the fans that the output of the heat removed) determines abnormalities and problems or failures equal to those resulting from the malfunction or blockage of the cooling fan, but also defects to the thermal sensor.

supply plug.

Printed Circuit Board puffed due to overheating of tracks near power

Battery problems The battery of the notebook has a certain life, that strictly depends on how it is loaded, and the weather conditions, but also and especially by the number of

www.riparazione-notebook.net Figura 9.7 - Laptop Battery: highlight the connector to the motherboard. This connector has always protected the contacts to avoid short circuits if it were to touch metal surfaces. 190

charging cycles which it is subjected, since each model has a maximum number of charge cycles exceeded which loses its quality. The typical battery pack failure is the loss of autonomy, in the sense that a new notebook that is going on for three hours in a row, with the passing of time will turn off after 2 hours and a half, then after two and so on. But when the computer will not turn on battery, it means that there is a fault in the internal circuit of the package or has shorted at least one of the elements, or the fuse is blown, and this, regardless of fault in the notebook, as such as the interruption of any battery protection fuse placed before the connector on the motherboard. When there is a loss of autonomy or a sharp drop in voltage even when battery is charged, there is not much to do we need to change the battery, or, if you have some familiarity with electronics, open the shell, look for the defective item and replace it; the same if defective items are more than one. The replacement of the elements you can do after having found compatible with those of the original battery, for example, in a NiMH battery - pack 12 V and 2,700 mAh NiMH cells there are 2.7 Ah. Aside from that, when the notebook is running only with the network and not on battery, before assuming the battery fails, make sure that the computer will load correctly, and this is done first and found that the fuse on the battery on the motherboard is in place (ie you must test it, with a multimeter, when PC is off, verifyng if shows electrical continuity) and if it is necessary to see if the charger provides the correct voltage, which can be determined with the tester placed on the measurement of voltages and putting the ferrules on the contacts mass (negative) and positive. Note that normally the ground contacts are two side by side and larger than the other, but is not always so, and in any case the ground contact of the battery is disposed on the tester with the resistance measurement of low value, bringing a tip on the track mass of the mainboard (that is in contact with the negative of the power supply plug) and the other on the contacts one at a time , until you find the ones that give continuity, ie zero or very few ohms of resistance. Only if the notebook provides the correct voltage, it can be assumed that the battery needs to be replaced, if there is no voltage is necessary to check the fuse or the main power supply/battery charger and replace the chip that governs it

www.riparazione-notebook.net Internal view fo a lithium ion battery pack. 191

Figure 9.9 Replacement parts for laptop batteries: they have the contacts made from tin-welded blades are available in various capacities.

or MOSFET that is damaged. Battery Tester To check whether a notebook battery is in good condition there are several methods, the simplest of which is identify the positive and negative contacts of discharge (so are called the electrodes from which it takes its power to power the computer and that may coincide with those in charge, used to charge the battery from the notebook) and check which voltage provides, in principle, for a 14.4 volt lithium-ion battery, the most widely used, consisting of four cells -a full charge must be read at least 14 volts. The battery must have at least 11 volts, otherwise it is easy now that some element has failed, in this regard it should be remembered that the battery cells lithium-ion battery should not drop below 2.8 volts, otherwise they degrade. If the measured voltages are in place, you can also do a test to check the maximum current delivery: in this regard, after charging the battery for a couple of hours, you have to apply them to contact discharge resistor power that taps a current equal to the battery capacity: for example, if the battery is 14.4 volts and 4400 mAh should be a resistance of 14.4/4.4=3.27 ohms (the power of the resistor should be approximately 40 W). When charged with this resistance, the battery has a voltage that their heads remained above 12.5 volts, in principle everything is fine, you can also try to connect a resistor of lower value, such as one that forces the battery to disburse 2C, ie the equivalent current of the double of its capacity, and see if the voltage is acceptable. Keep in mind that the lithium-ion battery can be discharged at currents of the order of three or four times the equivalent capacity. For NiMH batteries, the situation is similar, except that the voltage at full load Note that the lithium-ion batteries have the connector, usually, the contacts connected to the intermediate cells, which serve to balance the cells, and this because in this type of battery is more likely that a cell is charged to a voltage different from that of other, with

the result that the charger off prematurely, when the cells at a lower voltage still are not charged. Furthermore, if there are cells at a lower voltage they are stressed more. Balancing is normally done by the charger on the notebook, but not all laptops do. A part of the manual technique, the possibility exists to automatically test the batteries by means of special tester: these valuable tools are able to carry out comprehensive testing of charge/discharge, cell balancing and to predict the duration, the residual charge (ie, how much percentage of capacity the battery being tested is lost). Also have adapters to connect to connectors of all types of battery in trade. The most advanced tester can also communicate serially with the controller “smart” batteries that have them.

www.riparazione-notebook.net CHAPTER 10 VIDEO FAULTS This category encompasses all problems related to on-screen visualization of pictures on the notebook: many different inconveniences that can be broadly divided into three groups: video card faults, monitor faults and connection problems. Video card faults have to do with the video chip and the switch, if any, managing the routing of the image to the built-in display or an external monitor; Monitor faults are the intrinsic ones in the LCD matrix or in its backlighting. Lastly, connection problems could affect the external monitor connector, but also cables and connectors linking the motherboard to the built-in display. We also include in this category any problem related to the interaction between the chipset and the video card, that sometimes can alter the picture or prevent them from being displayed.

Video card faults They are characterized by the fact that the picture does not appear correctly but it is corrupted in some way, is shaky, or features color bars of various thickness and frequency; the picture could even not be there at all, and be replaced by black/white or colorful checkerboard patterns, stripes or squares. Whenever there are vertical stripes on the screen, whether over the actual picture or instead of it, there is a chance that the display is at fault. To resolve this dilemma, connect an external monitor to the appropriate connector and check what gets displayed on it; if the picture is the same as the one on the built-in display, the video card is at fault; if the picture is OK, the problem lies in the notebook’s LCD controller. A faulty LCD can cause the whole screen to be white. When the picture does not appear on neither the built-in display nor the external monitor, there are two possible causes: either the video card is faulty, or the solid-state switch managing the built-in monitor and the external monitor connector is damaged; in a case like this it is quite difficult to identify the exact cause, however - if it lies in the video card - has to do with the output section and not in the D/A converter. The Northbridge chipset, if the video chip is damaged to the point it cannot properly communicate with it, detects the anomaly and plays four beeps on the onboard tweeter. Therefore, if you turn the computer on and don’t see anything on screen, but hear four beeps, it means that the video card is seriously compromised, or possibly that its graphic chip has one or more pins disconnected, which are vital to its functioning and its bus communication with the chipset; “disconnected” means that there is a cold solder joint on some of the pins, resulting in a false contact. If the screen stays black but you can’t hear any beeping, a more serious fault could be suspected, as the video chip has a fault in its D/A converter, graphics processor or output section; in this case, it is sufficient to connect an external monitor and see what happens. A reminder regarding the connection of an external monitor: the video card on a notebook is able to detect its presence and adjust accordingly. To be precise, if a monitor is connected to the external VGA connector when the computer is turned on, he BIOS automatically switches the graphics output to the external monitor and deactivates the built-in LCD. Otherwise, the picture is shown on the LCD display and no signal is sent to

the external connection. After booting the computer normally, the display selection (builtin, external or both) can be made with the key combinations assigned to that purpose. If the computer does not show anything on the external monitor upon startup or after manual switching, but the picture is shown correctly on the LCD, then the switch -or at least the part of it routing the signal to the external connectoris at fault. A faulty video card can also cause other symptoms, e.g. causing the computer to hang during the execution of games or CAD software that make use of the 3D graphics instructions; in this case the software can terminate and Windows displays a warning dialog box about the failure of a software module, or a problem with an Nvidia DLL. Sometimes an error message about a failure in execution of an Nvidia DLL will appear without blocking the computer. In these cases there are problems with the video chipset (GPU), which is most likely one in the last generation of Nvidia GeForce. Lastly -but less frequently- when the video card is defective the computer may even fail to turn on; to be more precise, turns on then off immediately, blinking the power-on LED a few times; this mostly happens with low-range mainboards where the video circuitry is integrated in the chipset (some Nvidia and Intel ones, e.g. i945 and i965). Tackling video card failures Failures in the video circuitry can only be solved by replacing the graphics chip; however, especially on the most recent notebooks where BGA components are used, the cause is often a false contact caused by overheating. Portable computers have practically hit a physical limit: their computational performances have grown exponentially, while their size has been reduced; with the increase in computational speed (brought about by the increase in resolution, definition and image throughput) inevitably causes a higher power consumption, which in digital devices is invariably proportional to the speed of switching between logic states. Power consumption is crucial, because power gets dissipated as heat. In recent years, the operating voltage of the components has been reduced to try and limit consumption, but this is not sufficient anymore and all chips (CPUs, chipsets, video circuitry) are increasing their heat production and require adequate heat dissipation methods. Unfortunately, the wild race to shrinking the size of laptops sacrifices efficient cooling at the altar of aesthetics, so heat dispersion systems are limited to copper/aluminium heat sinks, gas piping reduced to a minimum, undersized fans and air intakes that are often insufficient, and get clogged easily with dust, so that less air than necessary can pass. These issues, coupled with the insufficient rigidity of notebook casings and motherboards, can cause one or more BGA contacts to detach because of excessive heat, meaning, the solder alloy softens, the the balls in the grid array lose their shape, and lose touch with their respective pads. It is true that not all contacts in a BGA, or any other chip, are actually needed; however, when the solder joint fracture occurs in one of the vital contacts, a fault - more or less evident - arises. So, sometimes a failure can be solved by re-soldering the video card BGA chip, i.e. going through the “reflow” process referred to in Chapter 8. How can you tell when the video card GPU is faulty or simply needs a reflow? Unless you have access to sophisticated tools and software, which are available almost exclusively to manufacturers and their authorized service centers, you have to proceed by trial and error. In the luckiest cases, all it takes to identify a false contact is turning on the laptop after removing the upper cover

and touch the video chip, pushing gently, or delicately bend the motherboard to see if anything changes. Using a can of freezing spray can be useful, by directing the flow on the video chip and checking for any changes. Cooling the chip may also help identifying failures within the chip, but only if they are triggered by a heat problem. To identify the video chip, look for BGA chips on the motherboard; if there is a separate video card, look for the largest integrated component on it. Most chips are labeled ATI or Nvidia, although sometimes the video circuitry is builtin in some Intel chipsets such as i815, i915 and i965, or Nvidia NForce. When you believe you have spotted the video chip, you can double-check in the producer’s data-book, or simply google their code and look for their data-sheet. Nvidia chip codes typically begin with G86-770, G86-630A2 or GF-7200 (Ge Force series), GF5200, GF5700, GF6200 and so on. ATI chips are usually named Radeon. Other graphics chips can be branded VIA-S3 or simply S3; in this case you have a (rare) VIA chipset with integrated S3 video circuitry. In any case, the video chip has a heat sink which makes it even easier to spot. Apart from the CPU which is easy to recognize, there will usually be only two or three chips with a heat sink, unless the chipset itself has its own cooling system (as found on old PCs based on Pentium II, Pentium III and the first models of Pentium IV, or AMD Athlon XP and 64).

Reflowing a BGA chip Literally, reflowing means applying flux for a second time, which is a good explanation of what the process entails: slipping under the BGA chip well fused flux, so it reaches all the solder joints and help heat to melt the tin. This way the solder joints are effectively redone, and the flux helps concentrating the soldering alloy on the pads of both the chip and the printed circuit board. In the presence of flux, the alloy melts and models itself automatically as a tiny ball, touching both the PCB pad and the corresponding BGA contact. Reflowing is therefore more than simply “heating up”, and is much more effective. Heating up the PCB and the chip does melt the solder joints, but any flux contained in them has by now lost its power, so the soldering is not homogeneous and concentrated on the pads; on the other hand, adding flux restores the factory conditions under which the soldering was originally performed, and is equivalent to re-soldering the BGA chip completely. Naturally, the procedure is carried out without physically detaching the component; its effectiveness is based on the fact that, by putting flux all around the chip and applying heat, the flux will melt and flow underneath the BGA; in practice, the flux does not always reach all areas and all joints, which is why this method is not effective in 100% of the cases. If the defective joints are located in an inner area of the chip, such as the center, the flux may not reach that area and perform its function. This especially happens with the largest chips such as Intel i965. To enhance the effectiveness, liquid flux can be used, making sure to apply it before applying heat or it will evaporate; cold application ensures good penetration underneath the IC. In any case, when using a flux paste, you should choose one of the less dense ones, specific for reflowing or SMD soldering, and not for BGA soldering.

In practice, reflowing is operated by heating up the PCB in order to keep the pads’ surface hot; when the temperature gets to around 100 °C (212 °F), spread the flux paste; when it gets to 140÷150 °C (284÷302 °F) heat the chip from above for 30 to 50 seconds, trying not to go above 220 °C (428 °F) for more

Figure 10.1 Placement of the mainboard on the machine for BGA and heating it through infrared lamp.

than fifteen seconds or so, stopping as soon as the BGA appears to come loose, or the flux starts to boil. Specific temperatures are indicated by manufacturers, as every chip has different thermal characteristics. You can tell the tin is molten when, pressing gently on the chip with a metal-tip screwdriver, the chip appears to move either sideways or down (avoid pressing too much, or the balls of two adjacent pads may touch each other causing a short circuit, requiring complete de-soldering and re-soldering of the BGA) When the soldering alloy is molten, turn off the heating from the top - or if possible, gradually decrease its temperature by ca. 2 °C (3.6 °F) per second (reflowing machines provide temperature probes to help follow temperature changes). Same goes for the bottom heater. Optimal temperatures and variation curves depend on the chip type. If needed, the thermal cycle described above can be repeated twice; more than that could irremediably damage the component. While executing this procedure, do not forget that the heater operates on the PCB, so if an appropriate regulation mechanism is not applied, the PCB can reach temperatures high enough to cause components on either side to detach or move, causing potentially irreparable damage. Therefore, when insisting with the top heater, or even before turning it on, it is advisable to turn off the lower heater.

Figure 10.2 Flux deposition on the edges of the chip BGA from work, and when the component is heated, the flux will

spread penetrating below its body and reaching, in theory, all

Another handy tip: gently pushing the chip sideways or down can help the soldering alloy to stick to the contacts. This should be done with a metallic tool with isolating handle (otherwise it will quickly become too hot to hold it in your hand) and with a very firm hand; a move of as little as one millimeter can be enough to short-circuit a row of contacts with the adjacent one, requiring removal and re-soldering of the chip. Similarly, if you press too hard, you may cause the balls of two adjacent pads to touch each other causing a short circuit, with the same consequences. Furthermore, make sure that the chip you are reflowing does not have any glue dots or lines on its sides or underneath it, because it would prevent the chip from being lowered down and make proper contacts between the pads and the tin balls and put the whole reflowing at risk. Glue dots should be removed with a tiny screwdriver or another metal tip, when the PCB is at around 100 °C (212 °F). It is not advisable to do it beyond 130 °C (266 °F) because the chip could detach itself. If the BGA is glued with a red resin, it can be removed only laterally, but not from the bottom of the chip. In this case it is advisable to cold-work it, by dissolving the glue with specific liquid called BGA Glue Remover. These solvents should always be cold-applied, or they will immediately evaporate and can even catch fire. They should be applied all around the glue: manufacturers suggest to surround the chip with cotton wool, a piece of cloth or a paper towel, then drench them with solvent and wait for a certain time, usually between one and five minutes. Glue Remover makes the glue on the sides softer, and easier to remove at room temperature; after it has evaporated, and the PCB is put on the heater of the reflowing machine, the glue will become very soft and easy to remove, as soon as the temperature gets to 80 °C (176 °F). Reflow Curves The reflowing method we have just described is generic, and at times may not be optimal for a particular chip; the best solution would be to have at our disposal a more sophisticated machine, allowing to set automatic working

Figure 10.3 On the left, glue treatment for BGA using the appropriate liquid product (it can see at the center) applied with a brush; on the right, removing glue spots with a tip tool,

Figure 10.4 On the left, protection of the printed circuit area around the chip to be heated to reflow: the metal tape should be within 3 to 4 mm from the edge of the BGA. On the right, heating of the chip aluminum reflects the light of the lamp and prevents overheating of the mainboard near to the chip.

sequences compliant with the temperature curves suggested by the BGA manufacturer. Such machines have been around for a while, and they allow to program a full reflowing (or even soldering) cycle, defining various phases with specific duration, target temperature, and optionally the temperature gradient (the speed of heating or cooling when the soldering or reflowing is done, in degrees per second). To summarize, reflowing is a process in four steps: 1. gradual pre-heating of the PCB at 2÷3 °C (3.6÷5.4 °F) per second; 2. heating of the chip to the flux activation temperature; 3. further heating to a temperature slightly above the melting point of the soldering alloy; 4. gradual controlled cooling. In the first step, any moisture that may be present on the joints and pads is eliminated while the temperature gradually rises to about 130 °C (266 °F); after which, the contacts should be kept for one to three minutes (following the chip manufacturer’s advice) at a temperature between 150 and 180 °C (302-356 °F) so that the flux can melt, spread itself, and clean the surfaces of the contacts (this is called “flux activation”). In the third step, temperature should be increased by 2÷3 °C (3.6÷5.4 °F) per second, until it gets to the melting point of the soldering alloy spheres; to avoid false contacts and cold solder joints, the body of the BGA should be kept above the melting point of the soldering alloy (210 °C or 410 °F for tin-lead alloys, 220 °C or 438 °F for RoHS-compliant) for about 60 seconds. These temperatures should be regarded as minimum limits: peaks of

220 °C (438 °F) and 240 °C (464 °F) are allowed, respectively for tin-lead and RoHScompliant. During this phase, the PCB temperature (which is also the temperature of the pads) should not go below 150 °C (302 °F). When the third step is completed, the cooling begins: temperature of both the

Figure 10.5 Sequence of steps of removal of a BGA chip: on the bottom to the right, printed circuit, from which was removed in a BGA chip. Note the thermal probe of the machine, constantly resting on the printed circuit board close to the chip, to detect the temperature.

bottom of the PCB and the BGA chip should be taken down at a gradient of 5 °C (9 °F) per second, or slightly faster. This is achieved by simply turning off the heaters, or by also activating a fan to make the cooling faster. Precautions before reflowing Using a soldering machine on cards already populated with components, or anyway belonging to a notebook, requires a series of precautions to avoid damaging any plastic part (that can be irremediably deformed) and components that are particularly heatsensitive, such as the batteries for the CMOS memory used by the system clock and BIOS settings, which may warp or even explode, especially if they happen to be on the PCB side facing the heating pad. Therefore, before securing a card to the BGA soldering machine: 1. detach any adhesive isolating plastic sheets applied to various areas of the PCB; 2. detach any rubber or foam rubber parts glued to the PCB; 3. remove any plastic parts that look vulnerable to deforming due to excessive heat, such as for example some details

of PCMCIA card readers; 4. disconnect and physically remove the batteries for the CMOS memory; 5. remove any Wi-Fi, Bluetooth or Modem modules. As to the plastic parts, it should be mentioned that usually the RAM sockets and card connectors are built with materials able to withstand the temperatures used in BGA assembling, as they are soldered with the same machines; but there are exceptions. Also remove any socket-mounted integrated circuits (namely, the CPU) unless soldered to the mainboard. In addition to the above mentioned details, before executing a reflow or the resoldering of a BGA chip, it is better to remove any metal clips or any brackets or backplates attached to heat-sinks on chipset, video chip or CPU; these parts are usually isolated from the PCB with a plastic sheet that could warp and lose its efficacy with heat. Sometimes these plastic sheets are overlaid or very close to surface-mounted components, and their warping coupled with the heat from the circuit board -can cause these components to move, rendering the card unusable. Heating a printed circuit board, especially with flux, could detach other components that are close or on the opposite side of the one we are operating on, so to avoid fatal damage, it is necessary to devise a way to confine the diffusion of heat to the area where it is actually needed. A very effective trick is to surround the BGA with kitchen aluminium foil, or an aluminium tape for exhaust repairing. Leave a 3÷4 mm allowance around the chip border. The aluminium foil or tape has a high reflecting power, so it reflects both light and infrared rays, and allows to limit very effectively the heating of the PCB in areas other than the one subject to treatment, where the temperature remains very close to the one set for the lower heater.

Figure 10.6 Some reflow curves of BGA chip welded with the normal lead-tin alloy: Above that for the compo

www.riparazione-notebook.net nents of’Altera and below that for Lattice. 203

Replacing a BGA Reflowing does not always solve all problems, sometimes because one or more solder joints are not restored, sometimes because the problem is not a cold solder joint or a false contact but the chip itself is defective. In this case it is necessary to replace it with a new one. Replacement of a BGA is similar to reflowing: first the PCB is placed on the dedicated machine, and the top surface is heated to 140÷150 °C (284÷302 °F); when this temperature has been reached, heat the BGA component surface up to 220÷240 °C (428÷464 °F), while prying the chip from one side using metal tweezers (picture 10.5) or the tip of a tiny flat screwdriver. As soon as the component is lifted it should be removed quickly; particular care should be taken in avoiding any sliding, that could cause tin to stick on adjacent components, or even worse, detaching them in combination with the heat applied to the PCB. At this point turn off the machine, wait until the card has cooled down to about 50 °C (122 °F), making it possible to touch it; with a soldering gun and a desoldering braid, wipe off the remaining tin from the pads, so that the surface is as even as possible. Removing the extra tin is best achieved with a flat-headed soldering gun: first cover the surface from which the BGA was removed with BGA flux paste (or reflow flux or the SMD flux seen in Chapter 8), then rub the spheres with the tip of a well-heated soldering gun. The soldering alloy will melt in large bubbles on the tip, which will require an occasional shaking of the soldering gun away from the card, or wiping it on a moist sponge of the soldering station. Once all soldering alloy has been removed from the pads, remove any traces of glue along the borders of the area, to get ready to solder in a new chip. After removing the tin and the glue, clean the pads and the whole BGA area with a solvent (isopropyl alcohol or trichloroethylene) and then, once the solvent has evaporated, spread a thin layer of BGA flux with the help of a paintbrush. This flux paste is rather dense, usually dark-colored and looks like mechanical grease).

Figure 10.7 - Cleaning the pads of the chip BGA: from left to right, the deposition of flux with a spatula, heating and aggregation of tin on the tip of the soldering iron, desoldering

Now place the card on the soldering machine again, and position the new integrated circuit (BGA chips usually come ready with soldering alloy spheres on their contacts) on the circuit board, carefully positioning it to match the square printed on the board. Then turn on the bottom heater and bring the surface to 150 °C (302 °F); once this temperature has been reached, turn on the top heater and bring the temperature to 220÷230 °C (428÷446 °F) until you see the BGA chip ease down on its soldering joints; usually this coincides with the boiling of the flux. Reballing procedure If reflowing was not successful, i.e. two or more contacts became one while pressing or moving the BGA, the chip must be re-soldered; almost always it has to be reballed, i.e. recreating from scratch the soldering alloy spherical contacts. Instead, if the thickness of alloy left on the BGA contacts is enough, it is possible to re-solder it (see Replacing a BGA, above) after wiping any soldering alloy left on the PCB pads. Except for this case, before re-soldering the BGA, here is the procedure for rebuilding the contact array: 1. After removing the chip, put it on the bench with the contact array facing up; 2. Spread flux on the surface; 3. Pass the tip of a soldering gun, at a temperature of 280÷300 °C (536÷572 °F) on the pads to melt the tin, which will merge in large drops on the soldering tip; when the drop gets large enough, shake the soldering gun (away from the BGA or anything that could be damaged by heat) to get rid of the tin. Repeat until all pads appear smooth and even; 4. Delicately lay a de-soldering braid on the pads and heat it with the soldering gun, so that all soldering alloy is absorbed; 5. when done with the chip’s pads, repeat points 3. and 4. on the PCB pads. After completing this procedure, give your card a break and remove it from the heating pad, where you will position the BGA chip upside down (i.e. with the printed side on the bottom), to prepare it for the reballing process. This consists in giving the chip a new set of soldering alloy spheres, which will allow it to be soldered. The process requires a package of soldering alloy spheres, a specific flux, a positioning tool (a small vise) and a grid pattern for the contacts; you also need a small spatula, and a hot air generator. Here is the procedure: 1. first of all lay the BGA, contact side up, on the base of the positioning tools, and position it precisely in the center using the regulation screws provided with tool; 2. once the BGA is in position, wipe the contact side with a specific reballing flux (it is a thick and dark paste) using a paintbrush or a spatula; the layer should be even and thin as

this flux is very effective; 3. position the grid pattern (they are available for sale for every type of package and pin layout, for all chipsets and video cards) so that its holes match the pads on the chip, and lock it with the clamps so it does not shift; 4. spread the soldering alloy spheres on the grid pattern (make sure you use the right diameter, often specified on the package) trying not to exceed in quantity, and distribute them evenly until there is one in every slot. Shaking the positioning tool sideways is useful to help the spheres to spread evenly; 5. remove the excess spheres, by scraping the grid pattern with a spatula; any spheres that are not in a slot will be removed and collected on the exit slide on the side of the positioning tool, and can be put back in their package. The viscosity of the flux will help retain the spheres in the slots 6. remove the grid pattern, paying attention not to shift the spheres, gently take the BGA from the positioning tool and use the hot air machine with a diffused jet (no nozzle) and low pressure to heat the contact side with the spheres. Temperature should be set between 300 and 320 °C (572÷608 °C); the jet should be kept at 3÷4 cm (1.2 to 1.6 in) from the chip, so that the spheres do not shift; 7. when the spheres become soft and shiny, keep heating for 15÷30 seconds more, until all spheres are soldered to their pad. The spheres of tin are soldered when, thanks to the flux, they turn into little humps on each of the BGA pads. At this point the component is ready to be soldered with the BGA machine. As an alternative to the hot air jet, which may cause the spheres to shift, the reballing can be performed in an electric oven at the same temperature between 300 and 320 °C (572÷608 °C), strictly for the time it takes to melt the spheres (the oven should be illuminated and allow you to see clearly what happens inside). Melting time is usually around two minutes. The oven should be electric or infrared; microwave ovens should be avoided at all costs, because it uses electromagnetic induction and would destroy the BGA! Please note that there are automatic ovens which can execute autonomously a preset or user-defined sequence. As yet another option, the spheres can be melted removing the BGA from the positioning tool and putting it upside down on the BGA soldering machine, bringing the lower side to 150 °C (302 °F) and the upper side to 220÷240 °C (428÷464 °F), until the spheres melt. Once the chip has been reballed, position the PCB on the soldering machine and heat it to about 150°C (302 °F). Once this temperature has been reached, put a generous amount of flux paste on the spheres on the contact side of the BGA, and position it on the PCB pads, making sure it is perfectly aligned to the silkscreened markings; the positioning should be performed using one or two pair of tweezers, as the card will be too hot for bare hands. Once the component is in position, it should be heated with the quartz lamp or any other device dedicated to the upper side (component side), reaching at least 230° C (446 °F); after a few seconds the chip should ease down, a demonstration that the soldering alloy spheres are melting. A few seconds more at 230 °C (446 °F) and the soldering will be complete. Experience helps a lot in choosing the right timing, as the exact time depends on the particular soldering machine and alloy used, and inevitably, only practice makes perfect. When using RoHS-compliant alloy spheres, the temperature should be 15÷20 °C (27-36 °F) higher, and pay extra attention in order to avoid damaging the chip, by turning off the

upper heater a few seconds after the chip has eased down. Should keeping the BGA component still prove difficult, it can be mechanically cold-fixed with a specific glue: after spreading the flux paste on the pads, position the BGA on the PCB before heating, apply at least a dot of BGA glue on each side of the component, and wait for the glue to dry or harden a bit. After this, the whole set can be positioned on the soldering machine, of course with the chip on the side which is not facing the heating pad. With this approach, the chip does not ease down and it is more difficult to understand when the soldering is actually performed: it takes some practice, and the following information can be used as a reference:

Figure 10.8 - Removal of tin balls from a BGA: on the left smears flux, while in the center melts and joins the solder using a soldering iron with a tip spatula. On the right, alternative

1. the heating pad should heat the PCB to 150÷155 °C (302÷311 °F), measured on its top side; 2. when this temperature is reached, the upper side should be heated to 220÷230 °C (428÷446 °F) when working with tin-lead spheres, or somewhat hotter (235÷250 °C, 455÷482 °F) for RoHS-compliant soldering alloy; the component should be kept at this temperature for about 10 seconds, then the upper heater should be turned off; this 10-second cycle should be repeated 3. the soldering can be deemed complete when the flux starts to boil and overflow from the bottom of the chip; after ten seconds of this condition, the soldering is usually complete. BGA soldering, reflowing or de-soldering can be achieved with automatic machines (such as the one shown in figures 10.12, 10.13 and 10.14) that are able to process an entire motherboard, by automatically a user-defined sequence; these machines are based on a microprocessor or PLC, have a display for user interaction, and can even lift the BGA with a vacuum pneumatic system: after the heating, the chip is captured, lifted and retained by a suction cup. The heating of the chip takes place both from the bottom (the PCB area immediately below it) and from the top, through interchangeable nozzles that direct the flow of hot air; meanwhile, an infrared heating base keeps the whole working area hot, so that the card does not suffer from thermal stress, which could cause problems if different areas of the PCB were to be heated at too different temperatures or change their temperatures at different gradients, damaging the soldering joints of the largest chips and causing false contacts. These machines allow for complete customization of the work phases, by defining the

different heating steps, their temperatures, and how long they should be applied, but also pauses for cooling down; their big advantage is precision and repeatability of soldering, de-soldering and reflowing operations. Once everything has been set (it may take some practice before finding the perfect temperature curves) operations are fast and successful, an ideal situation for repair labs

Figure 10.9 - Steps of the reball: clockwise, deposition of BGA in the tool positioning, application of flux to contacts, closing the tool with the template applied to the BGA, shedding of the spheres, introduction into the oven and execution of the program.

Figure 10.10 - Flux paste for reball (on the left), can containing speheres of soldering alloy (on the center) and template for the positioning of the balls for BGA (on the right).

who need to work on large quantities of cards. Usually there are two available cycles: soldering and de-soldering. In the former, also used for reflowing, the three heaters operate with timing and temperatures defined by the user based on experience and curves suggested by the BGA manufacturers; in the end, a fan cools down the card. In the latter, at the end of the cycle the chip is lifted and retained by a vacuum system, which keeps it up in the air until the user turns it off (when turning the vacuum retaining system off, the chip falls and must be caught in a cloth or a container). As usual, a fan will cool the card down when the operation is complete. Note that after a chip has been detached, it is advisable to wait some time before it is set free from the vacuum retaining device, so that the soldering alloy on its bottom can solidify, and not be dispersed or solder it to the container when the chip is left loose. The most sophisticated machines include a guiding system for BGA assembling, consisting in a camera that takes a picture of the PCB pads from above, and a software that superimposes the chip’s contact array on the image, so that by aligning the two patterns the user can be sure that the chip is positioned correctly.

Figure 10.11 - Tool for positioning of the solder balls with already inserted a template and full support for swirling so as to spread the beads: you can see the handler on both sides and upper part

Collateral damage to the video card After dealing with the problems that may affect the video card, whether it is external or integrated in the mainboard, let us examine the troubles arising from failures in the mechanism for switching the video signal between the LCD monitor and the external VGA connector; this switch is performed by a series of solid-state CMOS commutators that can be inside or outside of the video chip. In the latter case, we should look for the component that contains them: usually a CM2009 by ON Semiconductors (Fig. 10.15), or an equivalent IC. A failure in this IC can cause different symptoms: for example, the signal may be missing from the external video connector. This situation is simple to identify, because the LCD monitor works and an external monitor does not; however, if both the LCD monitor and the switch are faulty, diagnosing the actual problem can be very tricky and the only working method is by trial and error. Moving to a different kind

of problem, the on-screen picture can be altered by a problem in one cell of a video RAM, at least on those notebook mainboards where the video RAM resides in dedicated chips and is not a shared area of ordinary RAM; in this case, after assessing that the GPU is not faulty, you should de-solder all video RAM chips one by one, until the fault is isolated. The same is valid when the notebook does not display any video signal upon bootup, but is showing signs of activity (access to the hard disk or CD/DVD reader), or if the onboard tweeter beeps signaling a video card failure. Video RAM chips can be rectangular or square in shape, they are usually close to the GPU in an even number, which should make them easy to recognize; they have codes like K4J55323QF-GC20, H5GQ-1H24MJR, according to their capacity. For example, H5RS5223 is a 32-bit 512MB chip from Hynix, one of the most common video RAM manufacturers. These RAM chips are usually BGAs, so the de-soldering takes place by placing the card on the BGA machine and heat it up with the lower heater; once the

Treatment with automatic machine for processing of BGA: the upper nozzle (such as the lower one) must be chosen so that it completely covers the area of the component to be treated.

Figure 10.13 Detail of an automatic machine for the of work/rework of BGA: the upper heater blows air from the nozzle rectangular that appears above the card, while the bottom heater does the same with a second nozzle under the card; protected from the grid at the bottom there are the elements the base of the heater, which heats the printed circuit board.

whole card reaches a temperature of 140÷150 °C (284÷302 °F), setting the hot air machine to 350 °C (662 °F) the chips are detached and can be lifted with tweezers. Each time a chip is removed, the card must be cooled down and re-tested, to see if the fault disappears; if the symptoms do not change after removing the first chip, de-solder the second one too; if the problem persists, re-solder the first two chips and take away the other two. This procedure works if there are four RAM chips; if there are only two, it cannot be of much help. In this case it is easier to buy two new chips and replace them, because two chips make a memory bank for the video card: when removing one, the video card does not work anyway not because the remaining chip is faulty, but because the memory bank is not complete. Re-soldering a RAM chip takes place in the same way as other BGA chips, although the task is somewhat easier due to the lower number of contacts;

Figure 10.14 - Machine for work/rework of BGA is equipped with hot-air heaters top and bottom of the chip and the board of bottom heater (infrared); the activities of the three can be set independently using the same touch-screen panel that allows you to choose the processing and program cycles soldering. Desoldering, cooling and removal (done via a suction con

trolled separately).www.riparazione-notebook.net211 moreover, if the chip are lifted swiftly without any sliding, the soldering alloy spheres should keep their position and it should be possible to re-solder them without reballing, by spreading flux paste on both the chip contacts and the PCB pads, put the PCB on the BGA machine, heat it to 140÷150 °C (284÷302 °F), carefully position the RAM chip along the silkscreened markings, and heat the chip with the hot air flow. Repairing the video memory is easier and less invasive in those portable PCs with a separate video card, as there is no need to touch the motherboard, and in the worst case any damage arising from the repairing attempt can be solved by replacing the video card.

LCD faults It can be assumed that it is the fault LCD panel when the image does not appear at all but the screen is lit, gray, dark gray or white, or even when vertical lines appear variously colored and arranged more or less dense, or if the image appears for only a portion of the screen. The screen is obviously fault if due to a collision causes a physical breakdown or one or more cracks. Instead, if the picture is visible but is very dark despite being set to maximum brightness and contrast, means that the backlight is faulty, or that the light source must be running out. The same applies if the image appears as a dark shadow in the background, in which case the backlight just does not work. Regarding the failure of the LCD, it must be said that usually can not be repaired because it involves the control logic of the matrix or the matrix itself (connections, transistor of the rows and columns of the TFT), you just have to remove the panel and note the initials identification, usually written on a label on the back, then order the parts based on the Part Number (PN) and the possible Serial Number. Because computer manufacturers to provide them the

www.riparazione-notebook.net Pin-out and application schematic diagram of video switch CM2009. 212

Figure 10.16 Upper on the left, video RAM highlighted on a mainboard; on the right, Nvidia graphic chip. On the bottom, two steps of detaching of a video RAM IC in a mainbord equipped with an own video memory bank.

builders of LCD display (just to be clear, HP, Acer or Asus does not produce liquid crystal display…) the parts can also be ordered directly from the manufacturer’s code desumendone ( for example, Philips, LG- Philips, Toshiba, Samsung, etc..) when this is the label that brings him back. LCD panels are usually fixed with screws to the back half of the lid of the notebook, the disconnect, care must be taken to free them from the connections without pull or force the comb flat cables and connectors, which are very delicate and can be damaged. To access the LCD panel you have to remove the front half of the lid, freeing it from the tabs and before that by the screws, usually placed near the corners and hidden by rubber stoppers. If the failure is due to the backlight, you must first identify its origin, which is not one but can be searched in a variety of factors, with the backlighting in notebooks currently most used, namely fluorescent tubes (neon lamps), the fault may depend on: malfunction of the inverter DC / AC that powers the neon tubes ; a problem in the chipset that prevents the generation of the clock signal to the inverter DC / AC ; exhaustion or failure of a neon light. The third problem can be identified very easily by turning off the handset, then disconnecting the connection of the lamp ( or lamps, if there are more than one) and applying to the output connector of the inverter DC / AC tester with which to measure the voltage delivered by the same ; turning the computer, after a few moments must be legible a voltage of 130 to 160 volts. Alternatively, you can, if you have another neon tube of similar size, try to replace it without mounting it in the display and see what happens. If it is indeed faulty fluorescent tube, you have to remove it and change it to one of the

same size (theoretically voltage and operating current are equal ) if the pipe is inserted into the display, check what it believes and remove it: some

Figure 10.17 ATI video card for a laptop Acer 4730: is a card that is mounted separately in a dedicated slot (eg MXM format, which is what is the most popular). As it is costly, these drives have the advantage of allowing the repair work on the notebook without chip on the motherboard.

times it’s a small screw that blocks a bracket, while others are a piece or simple glue. The original hose should be pulled gently to avoid breakage inside the screen, the new one should be introduced with care and possibly even more attached with the system provided. Before closing the whole is useful to do a final check, also checking that the cables were not tight at some point metal or that the insulation is not compromised in this case when you turn on your computer you hear a hissing sound and it appears likely an electric discharge more or less obvious. Let’s see what to do in the first and in the second case examined, namely when there is no voltage, which should trigger the backlight : chipset that is faulty or the DC/AC inverters, the symptoms are quite similar and you can settle the question by analyzing only an oscilloscope line that carries the clock signal; must be said that not all laptops have the backlight turns off controlled by the chipset, and in those in which the DC/AC inverter is always powered when the neon tube is in place the problem can be caused by the lack of main inverter or the inverter itself. In the PC in which enters standby mode when the chipset suspends the clock signal for the inverter, you must first look for this signal, obviously not in the normal and standby power to locate the clock signal must first identify the main component inverter DC/AC, or the controller, easily distinguishable from any other chip because the latter are almost always single or complementary MOSFET and thus have houses TSSOP 4 +4 pin. From the integrated data-sheet is easily seen that the foot receives the clock : this is necessary to bring the tip of the oscilloscope (the mass must go to the mass of the laptop or negative ) and to verify the presence of the clock, which is a wave square. If there is no clock failure is in the chipset (maybe it’s just a cold solder to one of his contacts and is therefore convenient groped with reflow ), while if there is a fault means that the DC / AC inverters. The inverters are also used integrated controllers that generate the clock and that they are simply enabled by a logic signal coming from the chipset : one example is the O2Micro OZ9910 : This component is activated portandone a high level on the pin ENA ( Figure 10.19 and Figure 10.20 ). In this case you have to check the logic state on the enable line ( enable) and lacked understand

- when - what is due. What’s PC with the backlight of the screen to the electroluminescent sheet, using integrated circuits similar, since the sheet reaches the luminescence if subjected to a potential difference rather high, to obtain which from what can provide the battery must use the usual DC / AC inverters. The observations made so far on finding and repair of faults. A little different is the speech of PCs that have the backlit LED screen, because it operates at low voltage, in practice the system typically consists of a current regulator module, but it is handled (on/off) by control signal of the chipset. The signal is a simple logic level controller that controls the LEDs, then just go and look for the presence of this appears when the monitor is functioning, but first the backlight. If the enable signal is present but lacks enlightenment, the regulator is faulty and must be replaced, and if this seems to be working is necessary to check the

LCD screen seen from behind: you notice (highltghted by red arrows) the label with the serial number (PN) to be used to order the parts and the possible

Figure 10.19 - Typical inverter circuit for supply voltage and current to fluorescent back

Figure 10.20 Typical inverter circuit for fluorescent lamps control based on the integrated OZ9910: the driver is double stage complementary MOSFET, each of which controls a primary winding of the transformer.

electrical connections with the rows of LEDs and then the LEDs. In all eveniences the circuits are surface-mount, then the removal of the components and rewelding should be done with the machine at a jet of hot air and a pair of tweezers, because the inverter circuit is small and light, should fasten to a terminal that suspends in the air, so as to avoid warming the air with the work plan, and melt or burn the coating or other materials (such as floor mats to prevent scratching the computer case). The terminal also serves to hold the small board. Multi -lamp inverters adapt to screens Some notebooks, Acer and Sony, for example, have two screens with CCFL backlight lamps; their inverters consist of two final stages similar , each containing a transformer and power transistors. When the screen is broken and you can not find such a specialist two-lamp , you can change the inverter circuit so as to adapt it to display a single lamp, the amendment is necessary because it is not enough to just stick a cable of a lamp letting off that of the second (that there is) because in so doing, the inverter shuts down because it detects an anomaly. We must, however, proceed in two ways: connected to the output of the inverter unused dummy load; disconnect the power circuit of the inverter on the lamp (output) is not used. In the first case you put a load resistor on the output unused, it leaves the rated voltage (to be measured in order to know that the other lamp in normal conditions) and dissipates 2.5 watts at least. In this way, the inverter sees its outputs loaded equally and it is as if there were two CCFL lamps. In place of a single resistor, to share the footprint can use more in series or in series-parallel. Since the resistance very hot poses disposal problems of heat it produces, therefore, in the notebook where the plastic parts of the screen may become deformed or not there is space in the shell of the screen to accommodate the resistance , recourse must be had to the second solution, which is to disconnect the primary of the

transformer corresponding to the output of the lamp used (Figure 20.24). To understand what is the transformer just follow the connections on the PCB of the inverter , or, more simply, disconnect the primary winding of a transformer and then try to connect the lamp to one or the other out until you find the one with which the lamp lights up.

Failures of connections Sometimes the lack of vision on the screen image does not depend on the LCD or the video card, but the interruption or disconnection of one of the cables that carry signals from the mainboard to the monitor, one of the main causes of this is undoubtedly wear, ie the fact that opening and closing the monitor, the cables, which are so bent and stretched, in the long run they break. The interruption is never generalized, it affects one or more conductors before the others and is found in whatever the solution adopted by the manufacturer to carry signals: in fact, they are so much to stop the cables, as the plates (flat cable). Generally, the mistake is revealed by bending and lifting the lid several times, when the video image appears or disappears or becomes dark and then light returns. In this case, remove the cover of the notebook and also the upper part of the base of the container, and then locate the connection points (or connectors) of the connecting cable that carries the data to the monitor and replace. In modern notebook the screen cover usually incorporates a microphone and web-cam often, but sometimes more, which is why you have to find the right cable, make no mistake, you can follow the path, but in principle the cable monitor is usually only one and that is more robust, that looks like a ribbon. In some note

Figure 10.21 Inverter board used to control backlight of LCD display by

www.riparazione-notebook.net neon tubes (CCFL). 217

Figure 10.22 For desoldering SMD components with the technique of hot air, it is convenient to fix the inverter board on a table clamp with support.

book there are two cables: one that carries the signals of the real video ( sync, RGB colors) and one that carries the power for the matrix and the backlight, in addition to the clock signal or command to the inverter regulator or the backlight itself. LEDbacklightDisplay ¬ebooksvvoltage Although declared from manufacturers and traders as fully compatible, the TFT LCD display with LED backlight designed to replace those with traditional backlighting showed different adaptive problems, in particular with Acer notebook and Toshiba Satellite Pro In these cases, the backlight does not turn on (with the Acer) or make noise like a buzz (Toshiba Satellite Pro). In the case if display does non starts, the problem may arise from various eveniences: for example, a greater absorption by the LED backlit display, compared to the original, which is detected by the circuits on the motherboard of the notebook, which blocks the ‘ supply company. The increased absorption can also be caused by power supply voltage supplied from the computer to the circuit and a backlight inverter designed for the original: in fact, not surprisingly, in some notebook backlight does not turn fueling the PC with the AC / DC network but it works when the PC works is battery powered, since in the latter case the voltage supplied to the mainboard and the rest of the circuits is lower (a notebook that takes 19 V by the AC/DC can be operated with a battery 3 cell Li-ion 11.1

www.riparazione-notebook.net Removing the laptop screen: removing the front of the enclosure. 218

V or with a 4-cell 14.4 V). Indeed reduced voltage decreases the absorption of current by the display. Similarly, the Toshiba Satellite Pro (for example, in the model Toshiba Satellite Pro L45013N ) and in all the portable circuit in which the display backlight makes buzzing or other noise, going to battery power the same noise reduced almost to zero, reflecting the fact that lowering the voltage problems disappear. These situations can be resolved in one way : by interrupting the positive power wire that leads from the motherboard connector to the inverter and original by inserting a series voltage regulator that lowers the voltage from the classic 19 volt to 10 or so, in actually agrees to experiment by feeding the new display (LED backlight) with a laboratory power supply with adjustable output, in order to find the value of voltage that allows the backlight to function well without buzzing. The insertion of the power supply must be made by combining the mass of laptops with the negative of the latter , meaning the mass of the notebook the negative wire that leads to the backlight of the display, after interrupting the positive wire of the same backlight, just apply the positive supply to the positive input of the display backlight. Once this is done, we start from zero volts and salt until the backlight turns on steadily, illuminating well screen (the right level of brightness is reached when going up gradually with the brightness of the backlight power supply voltage does not increase appreciably. Found this value, you know the voltage that the regulator should provide. However, it should be borne in mind that the display “compatible”on the market work well with voltages between 6 and 20 volts DC; their absorption varies between 100 and 200 milliamps, depending on whether the model is the supply voltage. As a rule, having as a power supply stage of LED backlighting a DC/DC converter, the deeper you go with the voltage should be increased and the absorption (to maintain the same power supplied to the LED backlight ) . In the market there are linear regulators ( already discussed in Chapter 3 ) threeterminal (in TO-92 case) series 78Lxx, capable of delivering 100 mA and power dissipation of the order of 700 mW; to get an idea of the meaning the power (P), consider that depends on the voltage drop ( V) between input and output (ie between the terminals U and E of the IC) and the output current (Iu) according to the formula: P= VxIu So if your notebook provides 19 V and the regulator stabilizes its output voltage (which corresponds to the voltage required by the display to operate in optimum mode , as occurred with the variable power supply ) to 9 volts , the fall DV is equal to 19-12 = 7 volts. The power, if the backlight absorbs 100 mA , that is :

P=7Vx100mA=0.7 watts www.riparazione-notebook.net219 corresponding to 700 mW , ie a maximum bearable by integrated circuit. For higher powers can be used to more robust 78xx series regulators , encapsulated in TO-220, which provide up to 1.5 amps and bear powers, without heat sink (operating condition desirable because the heatsink requires space , not always available where you are going to enter the circuit modification) a little less than 3 watts (2.8 W is the maximum practically dissipated). Regarding the series regulators 78Lxx , are produced with voltages payable of 3.3V, 5V, 6V, 8V, 9V, 10V, 12V, 15V, 18V, 20V and 24V, for the modification of the circuit described here affect the voltages from 8V to 15V . As to 78XX, are available with output 5, 6, 8, 9, 12, 15 and 18 volts. For example, for the Toshiba Satellite Pro it is seen that the optimum voltage supply of the backlight is around 8 volts. If the optimum voltage required by the notebook being edited is not one of those provided by the standard controller, you can play on value adding silicon diodes: to be exact, a 1N4002 type diode in series with the output lowers the voltage of about 0.7 volts , and then placed at the output of a controller from 8 volts ( 78L08 or 7808 ) allows to obtain a little more than 7.3 volts. Placing a diode in series to the ground terminal ( M ) instead of the voltage supplied from the salt of about 0.7 V, so a 7808 having a diode in series to the M provides less than 8.7 volts.

Figure 10.24 - Modifying an inverter board for the LCD backlight to two lamps: one end of the wire to one of the two primary transformers has been removed (top photo) and isolated by paper tape, so that it does not touch other parts of the

Figura 10.25 - Collegamento di un regolatore di tensione 78xx all’alimentazione della retroilluminazione del notebook: i punti + e - a sinistra si collegano rispettivamente al positivo in arrivo dalla scheda madre (interrotto sulla schedina di modifica, così da non danneggiare il cavetto del PC) e alla massa comune, mentre il + di destra va al + interrotto dell’alimentazione della retroilluminazione dell’LCD.

It should be noted that if the diode in series with the output terminal must have the anode facing the latter, while in the M series must have the cathode to ground (thus the anode connected to the terminal M). The same applies adding Zener diodes, which, as explained in Chapter 3, however, must be connected to the opposite of the normal diodes, Zener obviously it will add or subtract a voltage equal to that of Zener. Another proven solution to avoid the buzzing computers such as the Toshiba Satellite Pro consists in interrupting the thread of the positive power of the backlight and insert a diode disposed towards the finish with the anode and the cathode to supply the display electronics controller (backlight power supply, add a capacitor (4.7 µF to 47-25 Vl) in parallel to the display, ie between the cathode of the diode and the ground contact of food, helps to improve the situation and to solve problems. All of these possibilities should nevertheless be tested in the field, because it is said that all go well on all notebooks; the latter solution has been tested on Toshiba Satellite Pro notebooks and it works very fine, but all depends from release and circuitry.

CHAPTER 11 FAULTS IN CPU, RAM, BIOS, CHIPSET When a notebook power on and starts but does not work, meaning that pressing the power button lights behave normally and the fan starts, then stop, but does not load the operating system or the boot screen (the BIOS) is not appear or freezes, it can be assumed a failure of the CPU and RAM. In this chapter we examine the two cases that can occur, starting with the issues related to the CPU. If there is a fault in the processor, usually the computer turns on but the screen is dark and there is no activity on the hard drive and CD/DVD drive, which is made evident by the fact that the activity light of these storage devices mass does not blink, the fan may start and then stop and resume later to run, or run continuously at full speed. In this case means that the processor heats much due to an internal short circuit or that the temperature sensor in its chip indicates thermal anomaly to manage heat of the fan. It is also possible, but rare, that a short circuit in the CPU face and then turn off your computer, but it only happens in those old PC in which the power that derives the Vcore and Vio voltages (power supply respectively the CPU core and ports I/O) circuits with unprotected or used also to power the chipset. It should be said that not always the CPU is faulty, and will not boot the computer and do not bring up the BIOS screen, and indeed sometimes the fault is more subtle and the computer seems to start correctly, but then it stops loading the system operating or during certain applications. In the case of Microsoft Windows, is the characteristic blue screen with an error indication and the reference to an instruction or a hexadecimal address, the error can also be signaled by a warning window, always bearing references to modules, addresses etc.. The symptom is closely dependent on which component of the CPU does not work: indeed, if there is a short-circuit on the ALU or is faulty or do not work the Program Counter and records, easily the PC even starts and you see only the lights work and the fan, however, if the problem is with the I/O or some control signal, we can verify these reports. When the fault is in the floating point calculations unit, the computer seems to work fine but report in programs that require this calculation, or advanced graphics software, CAD and three-dimensional modeling. In all cases so far mentioned, we need to find a CPU equal and try to replace it, recalling that before you have to reapply the heatsink spread a metal plate with the silicon paste white or silver thermal paste or other suitable means. The CPU can also be replaced with compatible models, according to the instructions of the manufacturer of your laptop and always considering this rule: even with different clock, the processor must have the same FSB bus frequency, or a frequency multiple. For example, you can mount a 2.8 GHz processor with 800 MHz bus instead of a 2.4 GHz to 400 MHz, which will be provided at a rate half that expected or older will reach 2.4 GHz This depends on how the Northbridge clock and manages internal clock multiplier. We must not, however, install a CPU bus with a 533 MHz or 667 MHz in laptops that have the original CPU at 400 or 800 MHz, because almost always it does not work; there are cases where the chipset of the handset is able to adapt to more FSB clock, but it depends on the computer. If the CPU functions but there are no problems with the unit of floating point calculations, the problem can also be revealed using special test software, the same goes for the registers or the ALU.

Problems with RAM If CPU also changing things do not improve, you may want to replace the RAM, because when it is broken, usually the notebook starts up but the display remains dark and does not perform any activity, the fan runs as if nothing had happened, in the sense that part and then stops, to start when the CPU gets hot enough. You also need to check that the RAM can not be incorrectly inserted and repeat the test by inserting a stick of memory at a time, so as to understand if there is a fault and splint which is responsible for it what is feasible and makes sense only if every stick of RAM form a complete bench, otherwise you should always install two sticks at a time. Sometimes problems with RAM are highlighted by a regular series of beeps (beep regularly clocked), which happens in laptops where the Northbridge chipset so provides and in cases where the defect is detected by the chipset itself. However, in many laptops if the RAM is broken or badly inserted, is not given any warning sound: the computer turns on, the fan runs as if nothing had happened, but do not you see and hear activity on the hard drives (not flashing the light of HD) and the screen remains switched off. It can also happen that the PC starts and then stops jamming on a screen during the loading of the operating system, or the PC hangs while running a program or gives an error screen refers to forms, etc. (this is the usual blue screen or alert windows already mentioned in sections reserved for failures of the CPU). In this case, the RAM needs to be replaced . In cheaper notebook computers, usually the video card uses the so-called Shared Memory: practically shares a portion of the RAM assigned by the BIOS and subtracted accordingly to programs, for use as video memory. In these cases, any problems of RAM can, in addition to manifesting the up mentioned symptoms, alter the image displayed on the screen or determine other defects correlated with the activity of the video card, this allows to identify with greater certainty a failure of the RAM compared to other cases. The replacement of the RAM must be done with compatible models, in particular, need to use a memory card that have the same clock or to support higher speeds. It should be said that some notebooks do not fit in memory “faster” and thus do not work properly, in which case it is mandatory to use memory modules that support the same clock. As for the laptops that use SDRAM, the available speeds are 66, 100 and 133 MHz, so in a notebook that mounts the PC66 (suitable to the system bus clock of 66 MHz) RAM can theoretically be replaced by memories PC100 or PC133. As for the computer with RAM type DDR, the available frequencies are 266 MHz (the memories operating at this frequency are called PC2100) 333 MHz (PC2700) or 400 MHz (PC3200); also in this case, theoretically a computer via bus 266MHz system can mount RAM to 333 or 400 MHz RAM Instead, if the originals are 333 MHz, you can use the 400 MHz, 266 MHz but not the most modern notebook mountain DDR-2, working with bus system 533 (PC4200) 566 (PC4300) 667 (PC5700) 733, 800 MHz (PC6400) or 1 GHz Older notebooks mounts memories EDO and in this case you have to check the access time, usually defined in nanoseconds (ns); the standard types (SODIMM) are suitable for the system bus at 66 MHz. Have recently made their appearance, in notebooks, DDR3, faster than the previous and characterized by a different position of the reference mark, is in fact said that normally, so that a memory can be installed on a computer that does not the supports, each type of stick

of RAM has a hollow in which a projection must fit into the socket of the PC. This measure is important because, in part differences in access time (which are of little importance) different categories of memory require different supply voltages and if mounting a RAM from 3.3 V in a socket of a computer that wants memories to 5 V, the stick is damaged. Another flaw is manifested in the typical RAM memory count and memory-test that the computer normally perform at startup, in some PCs, however, the welcome screen showing the logo of the manufacturer mask the startup phase, to display the which you have to press a key (spacebar or TAB) shown in the screen itself. Well, if the memory count is stopped and does not advance and the computer crashes, or if the proceeds cyclically counting to infinity and the start-up phase does not advance, it means that the BIOS has found an error in RAM. Often this error is reported in its start-up phase by means of a notice on the screen, sometimes not. Also in this case must be replaced the RAM in the notebook if multiple memory cards are mounted, proceed dismount them all trying booting the PC by mounting one at a time. It should however be noted that the initial memory-test can not always highlight the problems of RAM, because some defects do not occur at this phase, but then they come out of memory usage by the operating system; this happens because the RAM-test after power-on consists of simply reading and writing random data in ways other than those required by the operating system when you start the operating system, RAM is used in its full extent, as the CPU writes data bytes as large as the capacity of the memories themselves, or as the sum of memories, if your PC uses two memory benchs in cascade to form a complete memory bank (in the case of 32-bit CPUs that use 16-bit SODIMM: two makes a 32-bit bench).

Figure 11.1 - Access to the compartment containing the RAM usually clogs for memories are accessible from below, but there are computers (such as Texas Extensa) that have a socket under the keyboard and another mirror on the opposite side of the motherboard and accessible by a door in the lower part of the shell. In this case, to access all the RAM must remove the

Failure of the program memory If a problem occurs in the non-volatile memory containing the basic program of the computer, or the EEPROM or Flash-EPROM BIOS, the computer will

www.riparazione-notebook.net The Flash EPROM in which is located the BIOS of the notebook. 226

Figure 11.3 Some screenshot regarding setup pages of various Personal Computer having BIOS Phoenix, Award etc.).

not start normally, just as would happen in the event of CPU failure, but it can happen that it starts and remains stuck in one of the phases of startup, or when it shows the startup screen or should go for the RAM test or search for and list the disk drives present (this phase is called technically POST, or Power On Self test). If the fault is of this kind, before thinking about the BIOS must be groped to replace the RAM, mounting them one at a time and testing the notebook to see if the fault is not in them. Where can be excluded RAM and CPU, the problem is almost certainly in the EEPROM BIOS and in this case we can proceed in two ways: the first is to reprogram the memory or updating the BIOS, this procedure is accomplished by downloading a specific software utility and the executable file containing the new firmware (BIOS) from the website of the manufacturer of the laptop and copy it to a floppy disk, or on a Pen Drive or CD-ROM if your computer does not have a floppy disk but can to boot from removable disks or optical disc player. At this point you can boot and run the on-screen instructions, then install the new firmware. This operation is very delicate and it is important that when loading the executable file and the firmware does not turn off the laptop, otherwise it will stop loading the new BIOS and the computer runs out of the base system, then you can not restart it to repeat the installation of the new BIOS. If such an event occurs, you have to remove the EEPROM

that contains the BIOS and program it with a special programmer, or, if the notebook provides a connector for incircuit programming, proceed to load the new firmware by connecting to this

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Figura 11.4 CMOS battery: in this case is a rechargeable battery; the non rechargeable batteries it can be recognized because haven’t wires but rather are located in a specific plastic housing on the mainboard.

If in spite of the firmware upgrade the computer exhibits the same problem, you must replace the EEPROM or Flash-EPROM BIOS with a similar type, which clearly must be programmed before placing them in the notebook. The memory containing the BIOS is always in SMD and must be removed using the machine jet of hot air, after having sprinkled the terminals with flux to facilitate the fusion of the solder. Note that updating the BIOS is something that can only be done if the computer starts up and then crashes into the POST screen, if you do not start, you have to replace the Flash EROM and reprogram it.

Failure of backup battery In the Personal Computer is normally present a rechargeable battery that is used to maintain or operate the system clock (RTC, ie Real Time Clock) and that, in models in which the setup parameters are stored in a CMOS RAM , it also keeps computer settings. This cell or battery is usually of button-type, although in the past were used rechargeable batteries barrel formed by three elements NiCd 1.2 V each, for a total of 3.6 V. The voltage V 3 is standardized today, but we also use lithium-ion batteries, which provide 3.6 V. If the cell or battery is discharged, start the notebook shows the message “CMOS backup battery error” or “CMOS error” or a similar message, then boot stops and asks you to press a key to continue. This calls attention to the fact that the battery should be changed. If it happens that the battery is short-circuited, it may cause more serious prob

www.riparazione-notebook.net lithium button battery silver oxide used to power CMOS memory and make backup of its data. 228

lems and sometimes it may happen that the computer does not start at all, in the sense that turns on normally but fails to execute basic instructions, then hangs on the welcome screen or not shows nothing. This can happen -but quite rare- the problem is solved by removing the battery and checking how does the computer, and then replacing the battery if necessary.

Mistakes of the chipset As the integrated or the pair of integrated grouping together most of the logic of a computer, the chipset is responsible for a wide variety of problems finding described in various chapters of this volume; here can be summarized by dividing an accruals basis. MODEL OF NOTEBOOK GPU CHIPSET NORTHCHIPSET SOUTHBRIDGE BRIDGE HP TX1000 HP TX1350 HP DV1000 integrata nel northbridge NF-G6150-N-A2 NF-430-N-A3 NQ82915GM FW82801FBM HP DV6283 HP DV7 GF-GO7200-B-NA3 G96-630-A1 NF-SPP-100-N-A2 AC82PM45 AF82801IBM HP DV6000 MCP67M-A2 HP DV6200 GF-GO7200-B-NA3 NF-SPP-100-N-A2 HP DV6000 NF-G6150-N-A2 HP DV6500 LE82PM965 HP DV8283 HP DV9000 GF-GO7400-B-NA3 GF-GO7600-N-A2 QG82945PM NF-SPP-100-N-A2 HP DV9500 G86-770-A2 LE82PM965 SONY VAIO ATI RADEON P49932.00 SONY VAIO NH82801HBM Table 11.1 - Chipset and VGA IC’s of the mainboard of most common notebooks.

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Figure 11.6 Some chipsets: from the left, NVidia, Intel and AMD.

When is not well working, the Northbridge there may be problems of access to the RAM, the video card or general errors reported by the operating system and memory-related or addresses of devices such as the video, in which case it is not easy to discriminate the fault , although those that are specifically the competence of the video card are identifiable as described in Chapter 10 and memory failures are most evident, as explained a few paragraphs earlier in this chapter. Usually, when an error is reported in a form or a specific address, it is always better to look for in RAM and move towards the Northbridge and only after replacing the RAM and possibly the CPU, you can think of to get their hands on the chipset. Southbridge are the responsibility of the problems concerning the communication ports, access to the disk drive, keyboard and pointing device, the units of mass memory and the external PCMCIA or CardBus and in general the devices connected to the PCI bus or ISA, where they exist. The faults inherent in Southbridge are identified in a clearer and more unequivocal than the northbridge, apart from when it comes to problems involving the hard drives, which sometimes include a little of ambiguity, in the sense that sometimes leans on them to the controller or to same HD. Failures in integrated chipset or in Southbridge may also lead to failure to turn on the computer, however this usually can be inferred when the motherboard is properly powered in several respects, namely the DC/DC charger and internal work (this occurs through the oscilloscope, going to see the waveforms on the MOSFET, which is looking at the battery charge indicator) but pressing the power button on the PC will not turn on. Sometimes the fault of Southbridge block even the DC/DC main/charger: in this case, however, the other

DC/DC work, at least if they have the power independent from it. This behavior helps to understand where is the problem, that is, to discriminate against a failure of the chipset that blocks the supply/battery charger, but in fact it must be said that when the DC/DC charger does not start, may also depend on integrated circuit that governs it. When something is wrong with the Northbridge chipset, the streets are two: the replacement or, better yet, reflow, because this chipset is subjected to a discrete heating , since working with high clock frequencies (being in direct contact with the CPU) and therefore consumes a moderate energy, the strong heating -which also explains why the Northbridge is always cooled by a heat sink or fan- is often responsible for the posting of some welding, thanks to the deformation of PCB mainboard. The reflow or replacement of the Northbridge chipset to be conducted as explained in Chapter 10, about the video chip, it is, in fact, also in this case integrated in BGA package. Is also subject to overheating the integrated chipset (i.e. Northbridge +Southbridge): as it contains much more logical, most reason show more electricity absorption and dissipates more heat, even in this case reflow or replacement are the solutions. To get an idea of what can be the problem, that is, to discriminate against a cold solder or detached from a faulty chipset overheating due to internal chip , you can proceed experimentally trying to press on the chip body during operation up to slightly deform the mainboard , if there is a bad contact in the computer expresses its failure, but otherwise you can think of a damage of the silicon chip. This condition can be detected by blowing cold air or instant ice spray on the chipset when the computer is running and is hot, at least if the fault is found in cold, in which case, the sudden cooling of the integrated block should be computer or manifest defect. If your computer has trouble hot, you have to wait until the problem manifests itself, then cool the chipset to see what happens, or if the problem disappears. When instead it is suspected of being faulty the Southbridge, the preferential route is the replacement, because (except for certain computer) is not a component that heats it and so is hardly conceivable that one can unsolder the contacts due to the heat; reflow may be indicated because very often little foolish . However, even in this case the aerosol spray of ice can help discriminate the fault and if the notebook shows anomalies cooling the Southbridge, the hypothesis of the cold welding (and the consequent need of reflow) is not completely unwrapped. To identify the chipset remember what was said in the previous chapters, namely that it is one of the chip with heatsink or fan, know as well that are marked NVidia chipset, Intel (the symbol is often a lowercase i) ALI or VIA, although recently the AMD chipset provides integrated or Northbridge+Southbridge motherboards for HP or Compaq computer. The chipset NVidia NForce are the series and their theme song begins with NF (eg, NF -SPP -100 -M- A2) while those of the Intel begin with a letter preceding 82 followed by another three digits: for example Q82945PM (i945) G82965GM (i965) P82915 (i915) BD85HM55, BD82PM55 etc.

Failures in power supply of chips The malfunction of chipsets, GPU or CPU failure can depend on capacitors that filter feeds (many), principally digital supply lines; in fact, each power line, according to the manufacturer’s specifications (which vary from integrated to integrated) should be filtered

by a capacitor placed in parallel, ie between it and the mass, as close as possible to the pins or contacts. Sometimes in series to the line and the first filter capacitor (ie between the power source, the DC/DC or else it may be, and capacitors), an inductance is placed, which with the capacitor form a LC cell of the second order. These measures are intended to prevent the switching of the switching residues disturb the operation of digital circuits (CPUs can alter the execution of instructions, while in the chipset and GPU cause operational errors or even stoppage of operations) and also that a certain integrated circuit, which has the power supply in common with others, suffer of disorders induced by feeding them. These disorders may simply result from the absorption peaks, which, thanks to the strength of the tracks that lead from the power source, determine the line voltage sags impulsive; well, these pulses, propagating on a power line, can disturb other integrated which are more sensitive. The filters also capacitive and LC, are there to equalize the voltage so as to make it more uniform and to allow the operation of components such as CPU, chipset and GPU, which are the most delicate. CPU and GPU are themselves sources of the disorder, as on the supply lines absorb a lot of current, in an irregular manner, causing themselves disorder; for this reason their feeds are sorted on the spot by the tantalum electrolytic capacitors of relatively large capacity ( hundreds of microfarads on each line), that have the purpose of stabilizing the power supply providing a surplus of current when the integrated requires it. To prevent the absorption peaks disturb the rest of the components of the integrated video card, use insert filter inductances between these capacitors and DC/DC, and capacitors downstream of the choke, even to the DC/DC. The arrangement of the filter capacitor is normally recommended by the manufacturers of the chips, which also suggest the best layout nutrition; that’s why sometimes you see components arranged in certain positions, under the integrated. Usually the filter capacitors are placed under the chip because it is the position that allows you to approach them as much as possible to the power supply rails. And here is also the reason why sometimes manufacturers are resorting to unusual shape of the capacitors. A case in point concerns the highcapacity tantalum capacitor NEC/Tokin 0E907, mounted on motherboards of computers Toshiba Satellite A300 and in others, where it takes place under the CPU: this component contacts arranged to turn around immediately pitches under the CPU Unfortunately, the component has a limited life and when it goes into failure manifests leakage currents substantial and likely to bring down the voltage at the ends of the branches of power to the CPU; the defect may also appear from time to time and it becomes difficult to detect. Normally occurs by blocking the activity of the computer (screen stops and idle), but also with the smooth start which does not follow any on-screen display. In these cases, having tried replacing the RAM and CPU and disconnect the hard drive, if the problem can not be resolved should try desoldering this component (this is done with the car for the BGA or good hot air station, but in this case it is a bit more difficult) trying not exceed 220 ° C. By removing the NEC/Tokin PC should resume; the conditional is necessary because it fails the filtering action and the CPU can be affected. If removing the component of the PC begins to start right, you must obtain and install the tantalum capacitors in place by placing them between the tracks left uncovered; check what is the track using the mass flow meter placed on ohmetriche (just tap a track and the mass of the motherboard if there is a short circuit, that is the negative of the slope of the

capacitors). The electrolytic tantalum should be four 330 or 470 microfarad, 10V. The same goes, of course, for all the capacitors and for all computers if found to have abnormalities such as those described, go to measure the voltages on the capacitors tantalum placed on the power lines of CPU, GPU and chipset and proven to be stable and compatible with the expected value (typically 1.2 V or 1.6 Vsui core , and 3.3 V on I/O). With the oscilloscope, you can also check that the voltages are not affected by the various spikes and noise , which could mean that the capacitors have momentary losses that cause the lowering of the voltage pulse. You can also proceed systematically, unsolder one at a time (and reassembling those intact: if you loose a lot together you will never find the problem…) in capacitors that you suspect may be faulty, but this takes time. Identified capacitors responsible for the malfunction, replace them with items of a similar kind.

The NEC/Tokin 0E907 capacitor placed on the mainboard on the opposite side of PCB where it mounted CPU: this special capacitor is used to filter power supply of microprocessor. When it faults, stop CPU’s

CHAPTER 12 FAULTS IN MEMORY MASS UNITS This category includes problems regarding hard drives and optical disc drive, but also the other mass storage devices such as Memory Card, Memory Stick, and their respective readers built into the notebook. Such devices, in case of anomalies can give rise to multiple symptoms depending on the extent of the fault that has occurred in them. We analyze first of all the anomalies of the hard-disk: if the disk does not run for a motor failure or a mechanical problem, or because the electronics are not powered the mechanics (motor drive or magnetic disk head movement), the computer boot POST stops and almost always, after the self-test of memory, the BIOS reports the error message “HDD failure” in such cases, often do not hear the disc or turn this starts to turn to then stop cyclically. If, however, the interface is faulty or the internal controller to HD is not working, the computer does not recognize the disk and indicates that there is, and messages on the screen are “HDD not detected” or “HDD not present”. In this case normally feels and turn the disc in HD. The problem that prevents the operating system from starting or at least the hard drive can also be of another kind, and cover the head and the electronics that controls the movement, in this case, when it should start the operating system feels a “clack-clack” repeated, due to the attempt of HD positioning the heads on the disk to read the data. The noise continues cyclically and the system will not start. Another type of failure is what makes continuously vary the speed of the hard drive (which instead must rotate at constant speed) and that is felt from the outside, sometimes with a sound that becomes more acute, and then moves up in frequency becoming a hiss, all the cyclically. These problems are to correlate with the electric motor that rotates the disc or, more likely, with the electronic controller of the engine. In all these cases there is only one remedy: Replace the hard drive with a working one. In addition to this kind of problem, the hard drive can showcases others, while using the computer and operating system started, what happens when the fault is sporadic or looks hot. In such a case may appear error screens in the operating system (the classical bluescreen, for example) relating to modules or memory addresses, similar to those shown, for example, by Windows when the RAM has problems. Or the running program freezes and the keyboard and mouse are blocked or too unimportant, and in some cases this malfunction is accompanied by noises claims of HD, the type usually the “clack-clack” of the heads or continuous speed variations the hard drive motor. Also in this case the hard disk should be replaced. Sometimes, if the symptoms are limited to the block of the program running, but the disc runs and you do not feel special abnormal noises, agree to save the data while there is still time and then format the HD with special programs such as Disk Manager or disc Doctor; these utilities also have functions able to test the disc with regard to the ability to store data, the operation of the heads, as well as to verify the presence of bad sectors (zones of the magnetic surface that are not capable of keep the magnetization made by the head) or low-level format the disk. The latter should be used with caution, as in some cases can makes the disc unusable. The low-level format should not be confused with the one made by the operating system (which is high-level) as the one performed, for example, Microsoft Windows does nothing but prepare, organize storage areas in accordance with the FAT16, FAT32, or the NTFS, with the purpose of just allowing the operating system to

manage the disk and know where to write the data and where to go in search, while the low-level formatting erases materially

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Three screenshots of Disk

Manager; this software allow you to completely manage hard-disks, from verify of the magnetic support integrity to lowlevel formatting, ending to reallocation of MBR.

both the data, is any form of organization of the areas of storage and goes also to clear the Master Boot Record (boot sector of the disk, also called MBR) and thus prepares the disk to accept any partitioning. The problem is that some Microsoft operating systems to their limits or management problems associated controller on the motherboard or controller, if you delete the master boot record may have difficulty re-create a new one, for example because they are capable of looking only at a certain position of the disc. This concept is further clarified on the assumption that the hard disk is a magnetic surface arranged in a spiral, as such, can hold information in the form of residual magnetization due to the magnetic induction of the write head . The operating systems have programs more or less complex facts for “to seat” their magnetic data in this space; in the case of Windows 3.x, 95/98 and MS-DOS, using the FDISK, which serves purely and simply to prepare a standard hard drive for use with Microsoft programs, or to seek the master boot record (the one from which the controller starts to read and to boot) in a conventional position and write the extremes where find the partition you created. The partition is, as the name implies, a part of the magnetic surface of the disk on which to create a formal arrangement of the data, defined by the formatting (the FORMAT command, so to speak…) a high level. So FDISK creates a boot partition for the operating system, then the FORMAT command prepares formatting it according to the FAT or NTFS chosen. The limit of FDISK is that it is able to create the master boot record or boot partition that is not all start on the first available sector of the disk on the edge you can get around it by inserting at the beginning NON- DOS partition, which is useful for example, if the hard drive has bad sectors at the beginning. Also, if the disc is not prepared with a conventional position in the MBR, might not be able to create you FDISK partition. Instead management software disk as Disk Manager can do it and are able to relocate the Master Boot Record, or even low-level format the disk, to take away any kind of data, including MBR. Therefore, the low-level format is a real cancellation of the residual magnetization of hard drive, total, while the operating system is an organization of magnetic fields so that the same operating system to read and write to the disk, and you can only do after creating a partition whose location must have been previously written into the MBR of a disk management program and in any case at the factory. In light of all this talk, rather than low-level format the hard sometimes it is easier to update the Master Boot Record with the appropriate command in Disk Manager features, which makes the disc immediately reusable, this command is also available in boot disks for Microsoft Windows 98/Me and is the FDISK/mbr. As for the Microsoft NT-based operating systems, then NT, XP, Windows 7, there are other utilities such as DISKPART, but it should run from the operating system, since there is no bootable media. A separate discussion deserve more advanced operating systems, such as those based on UNIX architecture (Unix, Solaris, but also the various Linux distributions) which are able, as well as to prepare them in accordance with partitions (formatted as HPFS) also to create

and modify at will the Master Boot Record, which allows them to not have problems if you have to work hard with a lowlevel formatted. But not only operating systems such as these can be installed in hard disk drives in which there is already a partition of Microsoft Windows and can rewrite the Master Boot Record creating start menu run at boot, where the user can choose which OS to boot. Returning to the problems of the hard-disk, it should be noted that in the IDE/ATA, it may happen that a faulty hard-disk interface electronics arrivals to lock your computer, in the sense that prevents it from starting: the screen does not appear to anything, while the rest is working properly (the lights are on and the fan or the cooling fans running). In this case, to understand what is due to the block, you have to disconnect the hard drive and check what happens: if the notebook starts, or has the startup screen, it means that the HD has to be thrown away. In SCSI drives, where there is a controller evolved presidere the bus, the failure of a harddisk slow down the start of the time required to diagnose it, but usually does not cause the system to hang.

Faults in CD and DVD drives As for the problems of the optical disc drive, only occur when you try to read or write (in the case of burners) on an optical disk, or to start the installation of a program from them; the symptoms are typically frequent crashes or slowdowns loading the program or data transfer, accompanied by various noises due to the laser head that moves in an attempt to reach the tracks to read. It is not uncommon to hear the engine that accelerates and then stops, indicating that the controller or the motor that spins the disc have problems. Another thing is, however, if at startup, during the self- test of the BIOS is reporting optical disk failure: “Optical Disk Failure” or something similar, in which case there is a problem for the communication interface (IDE bus) drive or mainboard. Doubt settles replacing the optical drive with a new one and, of course, working. In special cases, the failure of the IDE interface can get to lock your computer, preventing the start: in practice, the notebook does not show anything on the screen, even if the light is “on” and the fan work properly. In this case, the doubt settles removing the CD/DVD drive and running the computer without: if part, the unit has a problem such as to block the IDE channel and should be replaced. Problems reading from or writing to optical drives, as well as locking the computer during these operations, they can also be traced to failures of the integrated controller on the motherboard, or interfaced to the Southbridge chipset built into it, in such cases the solution is interested in replacing the chip after it is identified. Other problems that can involve the optical disk drive concern special functions, such as the opening of the drawer, in rare computer is controlled from outside by a button cllocato in the notebook; is the case, for example, the Sony VAIO, whose player/DVD recorder button for opening/closing the drawer covered by the mask and opens and closes with a button located on the front of the PC. This function is obtained by sending the command via the interface S-ATA, but it is possible because the original firmware of the unit has been modified by inserting additional instructions to those of the S- ATA protocol that allow you to order the opening of the drawer. Replace this type of optical drives implies to find an original replacement provided by the manufacturer of the computer, otherwise,

while finding the same model from the same manufacturer of the optical drive, but not adjusted by the manufacturer (SONY) of the PC, it is almost certain that will be able to open and close the tray. In short, if the optical drive to a PC SONY is produced by LG and is called LG78ZZ for example, do not just buy one new signed LG78ZZ, but you need to order the replacement part at SONY because LG78ZZ leaves the factory with a standard firmware and responds to commands standard S-ATA, while that of the SONY is modified to work with SONY PC’s. Still on the subject of compatibility issues in replacing an optical drive, it should be noted that some houses modify the firmware of its readers/writers to force their repairers to order replacement parts, or do you build devices with interfaces suitably modified, an example concerned some Toshiba notebooks, in which the Cable Select signal was inverted with respect to the standard and therefore did not allow the notebook to recognize the presence of CD/DVD standard.

Problems in Memory -Card controller Defects readers to memory cards, the problems encountered are similar to those described for other mass storage devices: typical is the computer stops responding when you try to access these removable disks, or the error of timeout through a window of notice by the operating system. In this case we must first understand if the storage media is broken, that is, the Memory Card, or if something is wrong with the manager, or if any contact is broken or deformed in the reader, if the card is faulty you have to look for a new course, where it is deformed while some contacts, you have to straighten it out with tweezers. If this is not possible, it is necessary to replace the entire lock reader or the corresponding socket. Instead, if the card is good and contacts (which may be examined with a magnifying glass) are intact, the problem should be sought in the controller, which is an integrated circuit on the motherboard next to the hoof or player, in which case there remains that this integrated replace with a similar one. In this regard, note that one of the most widely used chip is produced by RICOH, and then tagged with this name, and this allows you to locate it better. However, the managers of Memory Cards are also produced by other semiconductor manufacturers, such as ON Semiconductor, ene and others. The failure of the controller or the posting of some contacts determinants for the recognition of the Memory-Card may prevent your computer from recognizing the type of card, or to see this device : in this case the operating system does not detect the device without understanding between those system in the case of Windows, in My Computer sends the corresponding icon and also restarting the notebook, since the issue is not resolved. Always problems to the controller may determine, in Microsoft Windows, warning messages such as: “Device not recognized”; in this case, even reinstalling the drivers and restarting nothing changes. Sometimes the lack of recognition or detection of the device depends on a fault in the DC/DC converter that supplies power to the controller, which at this point is not powered and obviously does not work; such a problem, as well as the failure of the controller, typically it turns out because in addition to not read the memory card, the notebook screen system resources does not show the controller, or exhibits an anomaly (exclamation mark or other symbol adopted for this purpose) in the corresponding device.

Problems in PCMCIA and CardBus controller Readers PCMCIA and CardBus more can support a variety of devices, not just memories, as in origin, but also modem, wireless interfaces, USB interfaces for notebooks that do not have them. When a failure of a device inserted into the reader occours, the corresponding function is not available, but the computer will not crash. If it fails, the controller PCMCIA or CardBus interface on the motherboard, this being interfaced to the Southbridge chipset may be a problem. However, usually not a malfunction of the controller locks out the operating system and is not binding on the operation of the rest of the computer, since they normally do not get to influence the activity of the CPU, but simply reports the error in the form of dialog box or abnormality (eg the classic exclamation point in Windows Explorer in Windows XP or in Windows 7, Device Manager). The failure of the control chip may also occur only when you try to access a device PCMCIA/CardBus. The speech is similar to the Smart Card reading devices, often connected via USB, but sometimes Intergate in the notebook for reading user authentication information or access to Internet services. The controller typically used to manage PCMCIA and CardBus are produced by various houses: for example Texas Instruments and Intel. some chips are an example i82559 Intel and Texas Instruments PCI7620. Other chips are built from ene, such as the UB6220, the UB6225 and UB6230; all three are of Multimedia Card Reader suitable to manage various types of memory card, so not only the devices but also CardBus MMC and memory Cards.

CHAPTER 13 FAULTS IN COMMUNICATION PORTS It may happen that a computer may not work COM ports or parallel, or USB, Firewire etc., and this is evidenced by the failure of devices connected to these ports, such as printers, scanners and more and signaling through a dialog box, the inability to find or communicate with those devices. It happens also that with the USB by plugging a device into the socket of the PC, the operating system crashes or is slow the execution of programs. Failures and mistakes like this are all due to the communication ports and peripherals related to, or even to that part of the Southbridge chipset that is responsible for interfacing with the communication controllers and adapters (USB Host, for example). However, if the issues are related to network connectivity failure, you should test ethernet interface, whether it is integrated into the motherboard or in the form of PCMCIA or CardBus device. In this chapter we analyze some typical situations that may affect the communication ports of the PC and the appropriate remedies.

COM ports and parallel Failures of serial and parallel ports generally proved inability to communicate with the device in the first case, or from defects in the networked scanner or printer prints strange characters in the second. The anomalies can be many and depend on which device is connected to these ports. As for the COM, typically used for modem or peripheral for control of electric motors, but also for measuring interfaces and data acquisition and for the programmers of memories and microprocessors used by developers firmware, the communication error is reported by the program that the uses, in which case, it is advisable first to think of a hardware failure, check the configuration of the COM and the correct installation of device drivers. If everything is in order, it means that something is wrong in the hardware of the notebook. Typically to fail are in the COM interfaces that provide for the conversion of TTL levels (5 or 3.3 V) in the RS232 -C (±12 V), ie the level shifters made by various integrated circuits, one of which is the very common MAX232 of Maxim. These components will fail for both overloads or incorrect cable connections to the devices connected to the serial interface, both to situations pretty random, and when the COM are connected to the modem, they can be damaged by an electric shock received from the telephone line and passed up the serial port. It should be noted that almost never, less than particular situazions, the chips involved are seen physically damaged (eg exploded or burnt) then you have to proceed in troubleshooting for exclusion, ie, procured the data-sheet, go and check with a multimeter, on pin TXD, if there are voltage levels provided at rest. In this regard, know that normally, in the absence of data, TXD must remain between 10 to 12 volts positive (inverted condition spacing), if there is no voltage, or what you read is less than 9 volts, something is wrong. Less frequent are the fault of the UART, now integrated into the Southbridge chipset and forcing the replacement of the latter. The serial port problems can manifest as time-out errors or failure to answer the device connected to COM, or failure detection thereof. As far as the parallel is usually managed by a dedicated chip, at least in older notebook, the newer ones that have had such an interface, is handled by the Southbridge chipset,

which is why if you are having problems with communication interfaces, and an analysis of the operating system and its drivers shows that everything is in place on the software, it becomes necessary to replace the Southbridge chipset or groped to submit it to reflow, in case some of his contacts in the unsoldered (just in case, however, quite rare). The ports COM and LPT (parallel) may not even work due to the failure of the power supply DC/DC that powers them; in this case, in addition to lacking voltage on the output lines and on those data (in parallel ) will notice that the legs feeding chip involved there are not provided either 5 or 3.3 volts.

Problems in the USB Such as Firewire, this communication port as well as communicate with devices connected to it can give them power and for this reason it is more prone to failure if overloaded. The 5 volt power supply comes from a dedicated power supply of notebooks, so in case the contacts 1 and 4 of the USB lacking the 5 volts necessary to seek the fault in this power supply DC/DC. If the problem is communication, you have to look in the USB controller, which can be achieved by various integrated circuits, an example of which is the FTDI’s FT232, USB controller chip them also produces the ene. When things go wrong in USB, it may cause many problems: for example, the

Figure 13.1 - Two kinds of USB connector for printed circuit board: connector is the spare part to get when USb connector on the mainboard is broken.

operating system can not recognize the device despite having installed the drivers and restarted the computer (Windows error message appears: “USB Device Not Recognized or unknown”) or crashes when connecting a device that connects to the device, however, there is no communication. To expose the USB problems on computers with Windows operating system also just enter the resources of the system and see if the icon USB Hub is reported anomaly. In all these cases you have to replace the controller, or groped to submit to reflow or replace the Southbridge chipset.

Troubleshooting the modem On computers with modems that are connected to the telephone line for a long time it may happen that the modem itself fails due to a voltage surge caused by lightning or interference , in which case any problems arise trying to connect, when the computer is reported that the line is absent. To ensure the fault is necessary to open the door that hides

the modem card (usually mounted on the motherboard but sometimes integrated in it) and watch carefully that there are no swollen or burnt components, because they can burn easily overvoltage protection diodes or resistors in series to the line connection, or the coupling transformer , which is essential for transferring signals to and from the line preserving galvanic isolation between the computer and the line itself.

Detach of connectors When the communication ports are working properly but there is no connectivity with peripherals connected to them, the problem may be with no doubt by the removal or corruption of matching connectors, in which case the fault is evident why, connectors appear as furniture or, looking closely, perhaps with the help of a lamp and a magnifying glass, although the connectors are stable some pins are disconnected. Usually the connectors you can move are the USB plug or phone, because they are more delicate; connectors DB- 9 and DB-25 used by serial and parallel are much more stable, not only because it held the largest number of contacts, but also because usually are screwed to the motherboard or to the container of the notebook. In case of more serious that a connector

Figure 13.2 Typical wireless module (sent on both sides) of a notebook computer; it must be inserted in a specific socket with retention clip.

is moving too, try to see if you can risaldarne contacts or the mounting tabs (which may be detached from the corresponding plots) with a soldering iron and solder, everything should be fine. If the connector has the mounting tabs broken, you have to desolder and replace it with a new one, proceeding in a similar manner as explained in Chapter 9 about the power plug:

basically you have, help you with desoldering iron and desoldering braid, remove the pond blocking contacts and anchor tabs, then pull out the connector by lifting it gently with a screwdriver blade. Extract the connector, with the usual desoldering braid cleaned the pads, then enter the new connector and solder it on the mainboard.

Faults of the wireless interface Whether it’s a Wi -Fi or Bluetooth, or an IrDA wireless interface defects are always the same symptom does not allow wireless communication, in fact, however, be done, this port provides a single channel that, in the case of connections via radio (the first two) is an electromagnetic wave high frequency while in

www.riparazione-notebook.net Chip ene tipically employed for managing of the USB communication ports and other units of notebook. 246

the IR is a light radiation at a certain wavelength. Regarding radio interfaces, communication takes place on a single carrier, then the symptom is always the same whether it faults the transmitter, which goes out of use both the receiver: in both cases there is no connection, and this may occur because turning on the wireless computer detects the device but not the presence of wireless networks in the surrounding area , which can detect the networks but fail (although it is properly configured) to establish communication. In this case you should replace the wireless module. If the device is not even recognized, the problem may be in the driver or, if this is correct and installed exactly in the processor that governs the interface, even in the latter case you should replace the wireless module, which is extracted easily seen which is always a separate card and never integrated (also for reasons of disturbances) in the mainboard. As for IR interface, the same considerations apply: if the section does not communicate is faulty transceiver, and if not detected is out of the chip that governs it, in which case you need to locate and replace the latter on the mainboard.

CHAPTER 14 FAULTS ON COOLING SYSTEM The cooling system and ventilation of a computer is of fundamental importance for his integrity, because if it is malfunctioning or not working at all, the critical components can overheat and become damaged, and for this, it provides devices that can monitor the CPU temperature (which is the most thermally stressed) and activate one or more fans strategically placed and aimed to remove the heat, bringing them out from the notebook. If in spite of the ventilation heat remains excessive, guards must turn off the computer; materially, the element that turns off the PC or sends it in standby is the chipset, which occurs by turning off the main power supply and the other DC / DC Notebook , but also by turning off the inverter LCD (this is obtained by depriving the inverter of the clock signal or to enable, according to the type of circuit used in the screen. In Chapter 9, it was mentioned that the integrated temperature sensors can prevent the start of a notebook when communicating incorrect data to the chipset, but may also have other problems, such as not to allow the start of the fans (even talking properly with the chipset) and lead to overheating of the CPU, GPU or chipset. Usually in this case is the final stage of the thermal sensor to fail, but this method only occurs in those integrated in addition to measuring the temperature and possibly inform the chipset, have a transistor to directly control the fan inside or fans of the notebook. Recall that the control is carried out usually by a rectangular voltage in PWM , so as to be able to vary at will the speed, increasing it if the CPU tends to overheat. The fans can still not start when it should, due to a failure of the external transistor that uses the sensor in order to control, or because they themselves are faulty.

Checking and replacing fans If a fan is not running or does not start ever in spite of the computer shuts down because he went overheated, you must first check if it is free to turn, or if something was stuck in the seat. If the fan does not turn although it is free or very endeavor, it means that is seized, or who hub has seized on the bearing; in this case must be replaced, first of all by identifying and removing the electrical connection, then going to look for where it is fixed. In this regard it should be said that in some notebook , to access the replacement fan need to disassemble the upper floor and with it the keyboard , while others just remove a door in the lower part of the shell. In others, unfortunately, is necessary to remove all the heatsinks and sometimes raise the motherboard, which entails a lengthening of the working times. Have recently been made of the fan SUNON maglev that work, so they suffers less the seizure because turn supported by an electromagnetic field and therefore their hub will wear less and this type of fan lasts much longer than a traditional and reduces the frequency of maintenance interventions. If the fan does not work is free to turn and when moved by hand wheel perfectly , it means that it is mechanically intact and why it does not work is to be found in its electrical part or the electronics of the motherboard. First you need to check the connection and, where this is in place (ie, the power connector is properly inserted) should remove it and try to see if the electric fan motor is in place, this verification can be done very easily with the tester switched on resistance measurements,

with a capacity of 1 kohm or so: just tap the contact red and black, one with a cap and with one another, and verify that the resistance is, at most, of the order of a few hundreds of ohms. If the resistance reading from the instrument is infinite or not measurable, it means that the motor coil is interrupted, then you need to replace the fan because you can not fix it. It can also happen that the fan or fans tadpole, but at a speed less than that required, and therefore the air flow is not sufficient to cool the computer, in this case heat can trigger the alarm and the PC may be turned off equally. Usually the abnormality is found by going to the Setup and verifying, where it is pres

Figure 14.1 - Opening the bottom of the notebook to access the cooling fan, which you can see the air inlet grid.

Figure 14.2 Fan and heatsink of a laptop wearing powder aggregate form of fluff: this type of dirt is very harmful because it prevents the heat sink to dissipate the heat and therefore can overheat the chipset and GPU.

ent the appropriate item, the rotational speed detected, or the presence of errors. In many notebook instead when the fan turns slowly, if it occurs at the start is signaled by a message during the bootstrap and the PC stops requesting confirmation startup. Still, sometimes the alarm or shutdown the computer can be caused by a malfunction of the speed sensor, or the lack -on- yellow wire of the fan signal that informs the chipset of the rotation speed, which is why, considering the fan still the chipset does not allow the notebook to boot even if the same is turning regularly. In all cases it is possible to verify the presence of the tacho signal using a frequency counter or oscilloscope: just connect the probe to the black wire with the town center and the tip (side terminal) to the yellow wire, PC is turned on. Clearly it is necessary that the fan is also connected to the computer, so you have to find the yellow and black. Alternatively, you can power the fan with a power supply of the appropriate voltage (5 or 12 Vdc). If the tachometer sensor works, on the oscilloscope screen appears the waveform, consisting of pulses quite regular, in the case of the frequency, the display shows the frequency of the tacho signal, from which date back to the speed. Accumulation of dirt One of the causes of the overheating of the CPU or the GPU, but also the chipset Northbridge, is the accumulation of dust and dirt on the ends of the finned heat sink in front of the fan, this is due to the fact that the air drawn by the fan through the slits of entry there is dust or soot in a more or less significant depending on the environment in which the computer is working. In the spring season, is also not uncommon to have pollen in the air, which will add to the possibility that the cooling system of your computer from getting clogged. This will affect the cooling system and makes it less effective, preventing prop

Figure 14.3 Insufflation of air into the space where the bearing and between the windings that are located under the rotor: the compressed air allows you to remove dust and lint very effectively, making the original cooling system efficiency.

er heat dissipation, and this problem in the majority of laptops generates overheating and consequent detachment of some welding of video chips (GPUs) especially if they are located to have a heat sink in common with that of the CPU and are placed, in the flow of heat, before the same CPU. In fact, if it is true that almost all laptops have a thermal sensor based on the intervention and the chipset (which turns off the computer if

necessary) is also true that such protection is based on the detection of the temperature of the CPU alone, so if it is to overheat the GPU, the sensor hardly notices and the PC continues to operate to the detriment of the video chip. This explains why in many notebook models , such as the HP Pavilion DVxxxx , often after a few years you are experiencing problems of representation of the image due to the fact that the chip is deformed, the solder balls that makes up the contacts (the GPU NVidia are used, and they are very hot in the case BGA ) melts or otherwise softens and does not stick when it cools more correctly, this causes the solder and, depending on which contacts are concerned, no longer allows the operation of the GPU, that determines a disturbed vision, squared and bars or more (image doubled, for example). In these cases usually the reflow of the chip is conclusive. When it is not decisive means that the GPU has any permanent damage (this happens more frequently in Intel i965 chipset with integrated video). To protect the cooling system in some notebook is placed a sponge filter at the input socket, then it is usually the filter clogged or filled with fluff. However, the accumulation of a lot of dust, soot and pollen at some point comes to clog the spaces of the heatsink, and despite the fan turns regularly, and also very hinders the escape of hot air that the fans must extract to maintain balance thermal. In this case it is necessary to disassemble the fan and, with a paintbrush or with the air jet of a compressor (or a more manageable laboratory canister containing compressed air) to remove the dust and dirt ; fact that you can replace the fan and the heatsink and verify that the computer running there is the right air flow. Sometimes the accumulated dirt going to focus in the fan bearing and, aided by the heat ( which can sometimes be very intense) creates real scale are likely to impede the rotation of the fan itself, which comes in turn bad, jerky or seize up. In this case you can groped to clean the fan spraying of the descaling type SVITOL between the frame and the inside of the rotor (where there is the motor) and then blowing with the canister of compressed air or by acting with a toothbrush (if it may also use a toothbrush); usually this intervention, perhaps, repeated, free the fan, but if not, replace them with the latter. Replace the fan is, normally, quite simple: it is sufficient to identify the two or three screws holding it, then remove it after having disconnected the power plug, clean the seat with a brush or an air jet and install the new one, then connect the power connector of the latter. As already mentioned, in the most favorable cases, the fan is accessible behind a door that is removed from under the notebook, but there are situations (for example, the series and DV6xxx Pavillon Pavillon DV9xxx HP ) in which you have to disassemble the entire computer.

CHAPTER 15 FAULTS OF KEYBOARD & TOUCH-PPAD The keyboard and mouse or touchpad on the notebook , like all computer parts, subject to failures of various kinds, meaning both the failures ascribed to them (electrical and mechanical in nature) as well as issues regarding integrated circuits that manages them, not least the Southbridge chipset. In this chapter, let’s discuss the most common, starting with the problems concerning the keyboard. The keyboard is subject to failure which can be either mechanical, or electrical; mechanical ones are represented by physical disruption of one of the buttons that make it up or by the removal of one of the keys (which are then, the plastic covers that come into contact with our fingers when we write) located above the buttons, but also the entire keyboard to crack due to a fall or a collision of the notebook. The electrical and electronic faults are represented by the oxidation of the contacts or their wear, given that in the portable PC using electromechanical keyboards almost always of the membrane type, very reliable, but still subject to oxidation or removal of the conductive layer. Then there are the electronics failures and relate to the Keyboard Encoder and the Southbridge chipset, these are not easy to solve and require interventions on the motherboard. The repair of the case always depends on the type and extent of the detected failure.

Faulty identification of the keyboard Aside from the physical breakage, which are identified by eye, other faults are to be sought in an orderly mode, we must first see what the symptoms are and to do it is appropriate to open a text editor for the keys of the alphanumeric characters. At this point, pressing a button does not appear if the corresponding character, you have to verify that you are pressing the buttons regularly and thoroughly, and if not, you need to see what fits them, or whether the suspension mechanism is not broken. In the membrane suspension is obtained from the same rubber membrane, which is shaped like a dome and off pushing the button at the top. If the buttons down but nevertheless nothing appears on the screen, it means that there is a fault in the keyboard or encoder, or in Southbridge, look for the fault in the keyboard should be removed and access to the strip, making sure the contacts of the rows and columns with the tester willing to measure resistance and continuity . Usually the connections of rows and columns are perceived by following the raceways under the membrane, or alternatively you must obtain the data-sheet of the keyboard, which is not uncommon on the Internet trying to find the code with any search engine (eg Google) . Locate the row and the column in which you must find the key defective, you are betting on a tip Tester positive and the other negative, then occurs, pressing the button, if there is continuity, if the resistance remains high, it means that the contacts of the key are oxidized, or the key is faulty. In such a case we have to change the keyboard. In addition to the alphanumeric keys you have to try all the other keys, such as Alt, AltGr, Num Lock, etc. Fn . If, during the dismantling of the keyboard to access the mainboard or make a reflow, when re-assembling the computer you see problems on rows of keys, it is likely that you close in bad connector or damaged the flat cable of the keyboard itself; if

this eventuality occours, try to pull it out and re-introduce it in its connector. If the keyboard is not damaged, it means that we must turn their attention to the keyboard encoder or Southbridge chipset or, more precisely, if you find that in addition to the mouse and keyboard does not work even the USB, it is likely that the fault is in the chipset Southbridge, so you have groped to submit it to reflow, or replace it with a working one. Instead, if it is not just the keyboard do not work or keyboard and touch -pad, it is likely that the problem has the keyboard encoder. Usually this type of integrated is a multifunctional addition to the keyboard and the touchpad controls,

www.riparazione-notebook.net View of the mechanics under the key of a notebook keyboard: it can see the suspension and articulation arms. 256

Figure 15.2 The identification code, to be used to request the replacement, is located on a label at the bottom of the keyboard.

any PS / 2 connection and the external devices connected to it, and more, a typical example of the chip is the KB3920 ene, which communicates via SMBus with the Southbridge chipset. So please try to locate in the motherboard, the chip and see if there are any bulges, burns, holes (a clear sign of an explosion of the component), in case of more serious one of these anomalies, you need to replace the chip. Replacement is recommended anyway, even if you do not see anything. Another chip that acts as a keyboard encoder and controller of the pointing device is the KB926QF, mounted in newer computers and always produced by the ene, from the same manufacturer are integrated KB3910, and KB3925 KB 3926, which among other functions can to perform PWM controller of the cooling fan of the notebook. In finding the replacement part, pay attention to detail: those of the ene controllers are programmable to perform various functions, normally programmed and customized specifically for a computer manufacturer, then you must make sure to find the same type, programmed in the same way, for a laptop, otherwise, that is, if you take the generic chip, you have to programmarvelo, which is not easy. In doing research, always indicate the entire code of the component, with all prefixes and suffixes.

Figure 15.3 -

Typical chips on the motherboard of the notebook they handle the keyboard

Faults of pointing device Figure 15.4 Two touch-pad: on the left, the sensor under the protective coating; on the right, a complete set of flat cable for connection to the motherboard and buttons to click and activate all the functions typical of pointing devices.

The mouse or touch-pad can present various kinds of faults on the basis of how it works: it is a small integrated trackball (for example in the Acer TravelMate 700 series a few) years ago may have problems of accuracy in positioning the pointer due to the accumulation of dirt in the rollers of the potentiometers, but can also lock in one direction due to a fault in one of potentiometers or the posting of a roller. If the pointing device is a small joystick (such as that of the old IBM Thinkpad and Toshiba Satellite a decade ago) defects that can accuse depend on the contacts of the four directions, it comes to small buttons and

therefore faults are the same keyboard. More complex is the problem in the touch-pad, which work with an array of capacitive sensors or charge transfer; this type of pointing device may present imprecision in the pointer to follow the position of the hand due to the deformation of the floor, or it can blow up the pointer across the screen. The deformation may occur due to an impact or for prolonged use. It can also happen that some contact comes off or that one or more cells go out of use or short-circuited, in which case the touch-pad will become inaccurate, or the pointer will proceed jerky, since some positions will fail to detect them Figure 15.5 - Operation of the capacitive touch-pad: between neighboring contacts, each having a capacity, the electric field transfers some charge; approaching finger, part of the electric charge is subtracted and discharged to the ground. The sensor detects the touch-pad and determica where the finger, as the contacts are many and arranged in a matrix, then it is easy to determine at what point a certain position in the array is the loss of charge.

correctly. Finally, if it fails the integrated deciphers the signals from the touchpad, it may either fail or give inaccurate positions, if it goes down the Southbridge chipset or its part that takes care of interfacing with the mouse, the touch -pad will not be detected and in any case will not work. It should be said that when it fails the southbridge typically occurs a series of failures generalized, involving the communication ports and keyboard. With regard to the failure of the controller of the touch-pad, the same applies as for the keyboard, since the integrated handles it normally also takes care of pointing device, and then, before putting his hand to the Southbridge chipset assessed the opportunity to buy and replace the multi-function controller, which is often one of the chips of the ene of which has been talked about two pages back. However, there are other manufacturers that make controller for keyboard and touch-pad, if you do not see a chip marked ene, try a few built- in square case PLCC QFN or near the attack for the keyboard and the touch -pad. More information on the chip ene (who are the ones most used) and their functionality can be found on the website of the manufacturer, www.ene.com.tw/en/. Among the faults that may involve the touch-pad and keyboard there is one very insidious because it is difficult to identify, such as found on some Sony VAIO: keyboard and touch-pad work only under BIOS or DOS mode while booted Windows or Linux operating stop working, on first examination this problem seems to be caused by a software error, or by the inadequacy of the driver used, but also by installing the latest drivers for your operating system , normally not resolved.

When this occurs, the cause is almost certainly the fault of the controller chip inside the touch-pad, which continues to direct the data to the controller on the motherboard, which is therefore constantly engaged on a data channel and can not detect the activities nor the touch -pad or keyboard. This problem does not occur with all the touch-pad controller and keyboard, but is found in many of them. In this case, to find the faulty component, disconnect the touch pad (the keyboard is not able to block the controller) and try to run the notebook without: if the keyboard is working properly, the fault is in the touch-pad, which therefore must be replaced. Please note that some chip controller touch pad and keyboard (eg KB3926QF -D2 ) also run the controller or other blocks of the main power supply, so they can also lock switch on the notebook.

CHAPTER 16 AUDIO FAULTS The audio device can, like all those in the computer, fail, and no longer work, or present various malfunctions such as signal distortion, noise or failure of the microphone input or line, experienced in the registration phase. The problems of the soundcard, understood as failures of the electronic part, they are still infrequent and is, if anything, more likely to be damaged physically one of the connectors (jack) input or output due to an excessive effort to introduce or remove the pins, of a fall or jerk the cable such as when you get up to the ears with the headphones and almost you are bringing your notebook. Other problems concern not the audio device, but rather the power ampflier that follows it, and that drives the internal speakers or external ones connected to the output jack, and sometimes may even develop a fault speakers, event, this, however, rare. If anything, it is most likely that your speakers are damaged by dropping or by the introduction (children are “masters” in this kind of “sabotage”…) of sharp foreign bodies in the notebook. In this chapter we will examine the various issues, each correlated with the action required.

Drawbacks in sound card Let’s start with problems that can affect the sound card, immediately making a distinction between the various blocks that make up this device and they are: the digital/analog converter; the analog to digital converter. The first is always present and reassembles (see Chapter 7), the sound signal into digital format generated by the CPU and the chipset past or extracted from the memory unit mass or downloaded from the internet while streaming, turning it into an analog voltage, and the second there is only if your sound card allows the acquisition of the low frequency signal, ie whether it has line input or microphone. In turn, these two elements can be free from defects partial or general : for general fault means the destruction of parts of the chip (for example due to overheating and melting and short circuit) that would completely block the audio device, while partial means a failure such as data bus with which the card communicates with the chipset to capture sound or send a dial tone or microphone already digitized. A partial failure is also affecting the analog section, ie the LF output of the analog signal or the audio input buffer before the analog / digital audio capture. It must be said that the sound chip is difficult to hurt, but if this happens, there is no audio signal or it may appear strongly distorted. However, the symptom depends strictly on the fault, so it is not only the absence or audio distortion, because it all depends on which section of the integrated sound card fails. For example, if the chip goes completely out of service or fails its digital part, the operating system does not recognize it at all, then the system resources the sound card does not appear, or if the problem is not widespread, it may happen that the card is recognized as present but not identified, in which case the signal is generated “device not recognized” or the computer indicates that it was not possible to install the drivers for the device.

Where to fail both the digital / analog converter, the computer regularly install the sound card, which is between devices in system resources and the operating system recognizes it working; however in this case the audio does not come nor to the speakers or possible line output. If the audio does not come to the speakers but is present in the output of the line, since the latter is just after the sound chip (ie downstream of its internal buffer) it can be assumed that the sound card functions but that fault is BF amplifier that drives the speakers or the power supply DC / DC that powers it, or that they work the same bad speakers. Instead, if the problem is in the output buffer, the sound is distorted. Let us now see what are the problems encountered in registration or acquisition of the signal from the microphone or line: if the sound is distorted, is responsible for the input buffer, but if the audio device, while being correctly installed and recognized by the system, does not acquire anything, it means that it is his fault analog/digital converter. In all cases in which are involved the converters ADC, DAC, internal buffers, the logic unit or the data bus of the sound chip, one must replace the latter, which is easily detectable because it is usually marked Analog Devices (eg AD1886 or anything else that starts with AD) Realtek, Creative or ALC ‘97, CML, Yamaha, Crystal or ESS. However, nowadays most of the notebook features, such as audio chip, the products of Realtek and Analog Devices, while Yamaha, Creative etc.. are manufacturers which mainly produce sound cards separate traditional PC or external audio to USB. Well, when the fault depends on the external amplifiers, you have to find them, they are usually small chip to 8 contacts or so, placed near the audio chip or close to the input connectors and output BF. The amplifiers that drive the speakers are typically equipped with a small metal flap with which they are fixed or soldered to the motherboard, and this makes them easily recognizable. You have to pay attention to the fact that sometimes the audio device does not work or play the sound because it may have broken down the power supply DC/DC that feeds or feeds the power amplifier to the speakers, in which case it is necessary to check with the tester if the power supply pin of the chip and audio amplifier (you can check what is this pin by consulting the data-sheet once you have discovered the initials of these components) receives the expected voltage with respect to ground (the negative of power, corresponding to the pitches with the mounting holes on the motherboard and the metal parts of the connectors). When the sound card is properly installed in your computer and recognized by the operating system does not come out signal and connecting to a headphone jack nothing changes, to see if it is a fault, the D/A converter chip or the audio amplifier of signal or power, must obtain oscilloscope and bring the tip into the leg of the chip corresponding to the output of the audio signal, you can locate this contact obtaining transportation the datasheet (Internet provides us this documentation: just type the abbreviation, followed by the datasheet, the component in Google or other search engine) of the component and displaying the pin- out (pinout). The ground contact of the tip should go to the mass of the notebook’s mainboard, the oscilloscope must be set with a time base to 1 or 0.5 ms/div and the amplitude to 0.1 V/div or so. If you start playing a song, if the oscilloscope shows a variable signal means that the sound chip works and so you need to devote their attention to the

Figure 16.1 - The speakers are placed in various ways depending on the notebook.

www.riparazione-notebook.net263 amplifier that follows, definitely dead. An empirical method to assess whether it is a fault, the D/A converter or if something is wrong in the amplifier is to play an audio CD, but this only works on computers (the fixed and notebooks definitely a bit less) where the CD ROM has audio output, and the latter is connected directly to the amplifier. In this case, if it is a fault, the digital/analog converter chip audio system sounds or MP3 will not play, while the audio Compact Disc yes. Any fault in the speaker It is very rare, but the speakers can fail, before seeing its problems should say a few words about how it is done and how the speaker. The speaker is a transducer that converts the direct current variable vibration in the surrounding air and is used to play sounds : controlled by a signal having a frequency between 20 and 20,000 Hz reproduces sound vibrations. Typically in portable equipment and where necessary quality reproduction of the entire range of the audio frequency, we adopt a single speaker, generic. In the reproduction of high-fidelity sound, each speaker is formed by several speakers, each of whom is working to reproduce a portion of the bandwidth (woofer, mid range and tweeter), this is because a single transducer, for their mechanical structure and acoustics, is not able to respond properly and uniformly in the entire band of the audio frequency. For example, the quality of external speakers for computers, often have two or three speakers. The speaker vibrates due to the current determined by the signal as applied, the current that flows from the two terminals in the coil, the latter is wrapped around the pole piece of a

Figure 16.2 - www.riparazione-notebook.netSome sound chips employed in notebooks: clockwise from top left, Analog 264

permanent magnet (also a time of an electromagnet) whose magnetic field is so that the signal current face move the coil. Given that the latter is rigidly connected to the membrane and that vibrates to the rhythm of the current flowing through it, comes a sound of the same frequency of the audio signal. The most significant characteristics of the speakers are the following : frequency response, indicating how the speaker behaves within the spectrum of audio frequencies (20 to 20,000 Hz) and is usually expressed as a graph showing the sound pressure to the reference power (typically 1 watt) to 1 meter or 50 cm away from the membrane, is expressed in Hz (Hertz); resonance frequency, is the frequency at which the electrical impedance reaches its maximum value, is expressed in Hz; electrical impedance, the impedance (in ohms) measured across the coil at a frequency of 1 kHz and should not be confused with the winding resistance measured with a meter, whichever is smaller, from notebook speakers have impedance ranges from 8 to 32 ohms; efficiency : the sound pressure is exerted at a distance conventional reference when the loudspeaker is driven by a variable electric signal (frequency of welldefined) that does dissipate 1 watt of power, expressed in dB / w / m, ie in dB measured at 1 meter away when the speaker dissipates 1 watt; rating power is the electrical power dissipated without limits of time, in continuous operation, with the coil driven in alternating current; music power, the power is bearable by averaging across the spectrum of a frequency response from the speaker, it is the most commonly used (improperly) to define the speakers from your computer. The speaker has a polarity that must be respected when you go to connect it to the amplifier output; certain works by reversing the connections, but the sound produced is inverted phase, which is of little importance if you listen to only one speaker but bother listening to stereo or speakers with multiple speakers. The positive (+) connects to the red wire of the cable (or those ending on the positive amplifier or audio jack) and the negative goes to the black (- output amplifier or audio jack). On the back of the component are usually shown the two essential data : the power and the electrical impedance. In notebooks, especially those equipped with speakers systems such as JBL, Bose or Harman Kardon (which are two major brands of hi -fi) speakers, albeit tiny, are able to provide great sound quality, thanks to the closure in small boxes that will turn off the rear output (which would negate the normal of the membrane) or convey it sideways to get the bass-reflex functioning and strengthen the bass tones, which are the most affected by small dimensioini allowed to speakers of the notebook. Well, having said that you can see what are the faults that may affect the speakers: the first is the burning of the coil caused by an electrical overload, which can result from excessive listening volume accompanied by strong distortion. It should be said that if the notebook is

well designed, the speakers are designed to withstand this condition, or for a more power than can be delivered by the amplifier’s audio device, but there is need to look to the effect of the distortion, which can lead to signal peaks able to put a strain on the voice coil. A fault of this kind can also occur in case the power stage of the amplifier goes into failure: in this case can provide a voltage higher than the ordinary one, and then the speaker is still subject to a power exceeding the tolerable, then fails, or excess voltage can blow up the amplifier and then pour the voice coil speaker surges, burning the thread that compose it. A short-circuit on final stage of power amplifier can cause a flow of direct current that can overload moving coil nad overheat it. If there is a power failure that damages the audio amplifier you do not hear any sound, however, if the voltage jump was momentary or left unharmed but the amp damaged the speaker, listening manifest irregularities. In this case and in all those in which the sound can be heard as the amplifier and the audio chip work, the main problem that occurs in the loudspeakers is that the overheating of the coil part dissolves in the enamel that covers the wire, reducing the ‘ insulation and shortcircuiting some turns: this results in a loss of efficiency of the speaker accompanied by a “caw” during playback of his, due both to the fact that the reduction of insulation lowers the impedance and then charge excessively the audio amplifier, is the carbonization of the paper which typically acts as a support to the coil. To ensure this we must open the notebook, disconnect the wires to the speakers and, with a meter placed on measuring resistance (flow ohmetriche) read the DC resistance of the coil, which in normal conditions is at least 80% of the impedance declared; the latter read it on the back of the speaker, which is normally stamped also rated power (find labels or markings printed as 0.2 W - 16 W etc..). If the resistance is much lower, it is certain that the coil is burned out.

Figure 16.3 - Cutaway of a loudspeaker: the voice coil is rigidly connected to the diaphragm (cone) which is held in place by the crawler (corrugated centering ring) at the base and from its upper edge (corrugated) outside.

In that case, replace the speaker or speakers failures. If, in spite of the resistance seems in place, the reproduced sound continues to be strongly distorted, it means that there is a problem in the amplifier, to resolve the doubt, connect the audio output of a pair of mini-stereo headphones or speakers and see how you can hear the audio in doing so, make sure that the notebook s audio output is amplified, which is equipped with amplification to drive a low load (8 to 32 ohm) impedance, otherwise if it is line output high impedance touches you use the speakers from the computer, but amplified. Unlike, it hearing sound weak and distorted. In addition to electrical causes, the speakers may be damaged due to a strong mechanical stress, due to the fall of the notebook or the penetration of a sharp object or to breakage of

the wall on which they are mounted speakers, perhaps as a result of a violent collision. These stresses can lead to vibration caused by mechanical detachment of the speaker or distortions caused by the tearing of the membrane of the transducers. It must be said that many speakers, including those from the computer, have the suspension of the membrane made of soft synthetic foam, which over the course of time, with the heat and the dry climate, it tends to dry out and crack, so if your computer speakers begin crackled after a certain number of years (if the notebook is a bit vetusto short,…) can not be excluded that the suspensions are torn, Even in this case the remedy consists in replacing the speakers.

The microphone It is a transducer that transforms the air vibrations in the sound components in a voltage or a current variation of the electric circuit in which it is located. The purpose is constructed so as to detect the acoustic vibrations, and then has a membrane, facing the outside either directly or through the holes or a thin grid, mechanically connected to an electric winding, a piezoelectric material, a coal (or other mechanically stressed that produces electrical effects) or metal plates. The microphone is a transducer analog, in the sense that the electric signal derived from it varies in frequency and in amplitude in analogy with the acoustic vibrations transmitted from the air. The type of signal that can be taken from a microphone depends on the fact that the transducer is active or passive : active means that generates a voltage, and if connected to a load (resistance) an electric current; passive means that the sound vibrations produce in it a resistance change, which may result in changes in voltage or current only fueling the transducer with a battery or power supply. There are various types of microphones, each born in a certain period and characterized by its prerogatives; generally used in laptops is that electret -condens

www.riparazione-notebook.net Internal schematic diagram of electret-condenser microphone, kind of microphone normally employed in notebooks. 267

er, because of small size, rugged, true plug- and low-voltage. The electret - condenser is a special condenser microphone : in it the vibrating membrane that moves due to the pressure exerted by sound waves, slightly shifts a metal plate which is located parallel to another equal, however, fixed. Applying a potential difference between the two plates (or electrodes) are witnessing a transfer of electric charge from the negative to that connected to the positive pole of the generator which gives the power; in rest conditions, once settled the charge does not flow no electric current. Instead, when the microphone picks up the acoustic vibration displacement of one of the plates determines a variation in the distance of the other, and then a new transfer of electric charge. Because when it moves a certain amount of charge occurs a current, connecting a resistor in series with the microphone and the battery that powers it occurs an electrical signal that varies in analogy with the performance of the sound waves picked up. The electret -condenser microphone is a condenser where one of the armatures is electrically charged by a special production process that allows elettrizzarla permanently. Usually the armor electrified is coated with a special plastic material. Electrification purpose is to make sure that the microphone has already its own electric field and therefore does not require external bias. Since it can not supply current, this microphone is usually coupled to a field effect transistor, integrated in its own container, is applied to the gate and the source of the JFET, and should not (and still could not) deliver any current, but, rather, to intervene, with its own signal, on the polarization. The transistor works in the open-drain configuration and requires a bias resistor of the value of some kohm. The supply voltage of the electret capsules is between just over 3 and 9 volt, while the output impedance, adapted from the transistor, is about 600 ohms. The capsule electret is in the form of a cylinder and, for its small size (between 1 cm and 3 mm in diameter) is the microphone favorite for the equipment in miniature (portable recorders, microphones pocket, bugs). Are commercially capsules two-and three wires: in the first transistor is an open-drain, and the positive terminal is the output that is the point to which to connect the resistor power; in the second output is distinct from +, which is the contact resistance which connect the power supply of the internal amplifier, formed by one or more transistors. Faults of the microphone The computer’s microphone is headed by the entrance to the sound card, or the analog/digital converter of the latter, which is often coupled with a voltage amplifier to op. If it fails, it is not possible or record sound from your sound card through it, or make telephone calls via the Internet telephony; inability to use the microphone can also be caused by a failure of the operational amplifier that amplifies the signal, but this is very rare and it is not easy to distinguish

Figure 16.5 Header of a notebook on which houses the audio jack (speaker output, line output and input line), and some components amplification stages, on computers that have the connectors on a card apart from the replacement of the same is more easy.

which of the components determines the problem. To understand it must be developed through oscilloscope and connect the probe tip to the positive of the capsule and the mass to the mass of the computer or the negative side of the same microphone capsule, see what happens speaking, if the microphone provides its own signal, the oscilloscope shows the ‘ corresponding wave. In the case the microphone is faulty, the screen of the instrument nothing appears. If the microphone is working but you can not record or talk on the phone, you have to identify the operational amplifies the microphone signal, obtain its datasheet and point the probe of the oscilloscope to its output (ie the audio input of chip on the sound card, this also detectable with the corresponding datasheet) to see if there is signal. If you do not record any audio component in spite of the leaders of the microphone there is, the amplifier is faulty. Note that these are weak signals, the oscilloscope must be operated with a probe x1 and vertical amplitude set to the minimum possible, ie to 0.1 V/div. The time base must be congruous with the audio band occupied by the voice : okay 1 ms/div. The microphone is usually placed in the casing of the laptop’s screen, which is why you have to replace it or at least remove the monitor, remove the front part of its wrapping if the microphone is supplied with a spare cable, you have to remove the upper part of the under the notebook and the keyboard to reach the cable connection on the motherboard. In the notebook when the microphone is on the base, there is less work to do: we need to remove the upper part of the shell of the base or any door which gives access to the microphone.

Damage to the jack It may happen that forcing a plug in the long run not warp, break or dissaldino the jacks, in which case it is convenient to replace the latter with suitable models, which fortunately are easily found in common electronics stores because standardized (with some exceptions, of course). To remove the jack you have to disassemble the base of the notebook and get to the card where are mounted until you enter the solder side, the jacks are typically on the motherboard, but sometimes found on other small cards that are home to other connections, such jack with LEDs

IR receiver Figure 16.6 - The jack on the right in this board hides the LEDs: they are the transmitters of the infrared port, the receiver which is on the left, but distinct.

as nutrition, the phone jack of the modem. In this case the repair is easier because you just pull the card out and replace them, then put it back in place and reassemble the notebook, without affecting the motherboard. Remove the jack of the audio is not as simple as it seems, at least if these are the type with metal screen and many contacts, this is because the legs are very thin and the holes of the printed matter where they are located rather close. Working with the desoldering iron does not always remove all of the solder that is used to remove the jack in a clean way you have to repeat the maneuver several times, maybe when the melting of the new pond succhiastagno hard to pick up. Since the tracks are rather fragile, it must be very careful and you have to avoid forcing the jack while you remove them, otherwise it is easily removed along with the metallization of the contact holes and destroy the connection so often that it achieves between the slopes of the two or more faces the printed circuit board. When removing the jack of the audio needs to pay attention to the fact that in some laptops hides one of the LEDs is the case of what Figure 16.6 shows the base that houses the jack, where the one on the right at the bottom is open and gives access to the LEDs, which are the transmitters of the infrared IR port.

The audio jacks are usually placed on the front or side of the notebook; extracting the plugs need to pull without flex, otherwise it is easy to damage or tear the outlets, which usually have the plastic wrapping and are anchored to the motherboard only dbolmente via the terminals