Reading Schematic

The purpose of electronic circuits is to control the flow of electric currents, it has been found experimentally that the intensity of various electrical effects is related to the amount of the charge that passes by a certain region per unit time. By controlling this amount we can vary the intensity of these effects. That's why this quantity , which is called the current, presents a special interest in engineering.

In practice, the flow of the current can be controlled by various electronic components. A network of interconnected components that can accomplish a certain task is referred to as electronic circuit. 
The current can be measured by an ammeter. A voltmeter can be just an ammeter with a series-connected high-value resistor through which the current proportional to the measured voltage is forced to flow. 

Impedance by definition is the ratio of the voltage to the current. Components in a circuit can be connected in series or in parallel With series connection, the same current flows through all elements and impedances add up. With parallel connection the same voltage is applied to all elements and conductances add up. In both cases the location of any element in the chain does not matter

Every circuit design starts with the development of a schematic. A schematic diagram is a drawing where components are represented by graphical symbols and that can communicate information about a circuit.

Before starting to find the problem on the motherboard we will try to implement the symbol and layout components contained / schematic diagram depicted on the motherboard, so we understand where the portion referred to in the diagram on the motherboard. This tutorial should turn you into a fully literate schematic reader! We’ll go over all of the fundamental schematic symbols:

Component  Symbol ,Caracteristic and How to test

Capacitors (Presented as Leter C or PC)

There are two commonly used capacitor symbols. One symbol represents a polarized (usually electrolytic or tantalum) capacitor, and the other is for non-polarized caps. In each case there are two terminals, running perpendicularly into plates.
The symbol with one curved plate indicates that the capacitor is polarized. The curved plate represents the cathode of the capacitor, which should be at a lower voltage than the positive, anode pin. A plus sign might also be added to the positive pin of the polarized capacitor symbol.

HOW A CAPACITOR WORKS

There are two ways to describe how a capacitor works. Both are correct and you have to combine them to get a full picture. 
A capacitor has INFINITE resistance between one lead and the other. 
This means no current flows through a capacitor. But it works in another way. 
Suppose you have a strong magnet on one side of a door and a piece of metal on the other. By sliding the magnet up and down the door, the metal rises and falls. 
The metal can be connected to a pump and you can pump water by sliding the magnet up and down. 

A capacitor works in exactly the same way. 
If you raise a voltage on one lead of a capacitor, the other lead will rise to the same voltage. This needs more explaining - we are keeping the discussion simple. 
It works just like the magnetic field of the magnet through a door. 

The next concept is this:
Capacitors are equivalent to a tiny rechargeable battery. 
They store energy when the supply-voltage is present and release it when the supply drops. 
These two concepts can be used in many ways and that's why capacitors perform tasks such as filtering, time-delays, passing a signal from one stage to another and create many different effects in a circuit.

DECOUPLING CAPACITORS

A Decoupling Capacitor can severe one, two or three functions. You need to think of a decoupling capacitor as a miniature battery with the ability to deliver a brief pulse of energy when ever the line-voltage drops and also absorb a brief pulse of energy when ever the line voltage rises (or spikes). 

Decoupling capacitor can range from 100n to 1,000u. 
100n capacitors are designed to absorb spikes and also have the effect of tightening-up the rails for high frequencies. They have no effect on low frequencies such as audio frequencies. 
These capacitors are generally ceramic and have very low internal impedance and thus they can operate at high frequencies. 

Capacitors above about 10u are used for decoupling and these are nearly always electrolytics. 
Decoupling means "tightening-up the power rails." The electrolytic acts just like a miniature rechargeable battery, supplying a small number of components in a circuit with a smooth and stable voltage. 

The electrolytic is usually fed from a dropper resistor and this resistor charges the electrolytic and adds to the ability of the electrolytic to create a "separate power supply."
These two components help remove spikes as an electrolytic cannot remove spikes if connected directly to the supply rails - it's internal impedance is high and the spikes are not absorbed. 

Decoupling capacitors are very difficult to test. 
They rarely fail but if a project is suffering from unknown glitches and spikes, it is best to simply add more 100n decoupling caps on the underside of the board and replace all electrolytics. 
Some small electrolytics will dry out due to faulty manufacture and simply replacing every one on a board will solve the problem. 

Some of the functions of a decoupling capacitor are: 
Removing ripple - hum or buzz in the background of an amplifier
Removing glitches or spikes.
Separating one stage from another to reduce or remove MOTORBOATING - a low frequency sound due to the output putting a pulse on the power rails that is picked up by the pre-amplifier section and amplified.

Diode (Presented as leter D or PD)

 

Basic diodes are usually represented with a triangle pressed up against a line. Diodes are also polarized, so each of the two terminals require distinguishing identifiers. The positive, anode is the terminal running into the flat edge of the triangle. The negative, cathode extends out of the line in the symbol

Measuring Diodes Voltage on circuit having 2 way ,it's depend on diode application on circuit. The Picture above showing in same direction diode ,Pin 1 as an input and should be passing the voltage to the pin2 output with same vallue ,voltage will flow to the arrow direction and not allow to install  reverse direction . in other application look at figur 2 diode having pin to the ground, this diode not pass the voltage .pin 1 should be in zerro voltage .if this diode having continuity short will happened.

CONTINUITY TES

Some multimeters have a "buzzer" that detects when the probes are touching each other or the resistance between the probes is very LOW. This is called a CONTINUITY TESTER. 
You can use the resistance scale "x1" or "x10" to detect low values of resistance. 
Set the pointer to "0" (right end of the scale) by touching the probes together and adjusting the "zero ohms" control. 
When taking a reading, you will have to decide if a low value of resistance is a short-circuit or an "operating value." 
For instance, the cold resistance of a 12v car globe is very low (about 2 ohms) and it increases (about 6 times) to 12 ohms when hot. 
The "resistance of a circuit" may be very low as the electrolytics in the circuit are uncharged. This may not indicate a true "short-circuit."
The measurement across a diode is not a resistance-value but a "voltage-drop" and that is why the needle swings nearly full-scale. 
Leads and wires and cords have a small resistance and depending on the length of the lead, this small resistance may be affecting a circuit. 
Remember this:
When a circuit takes 1 amp, and the resistance of the leads is 1 ohm, the voltage drop across the leads will be 1v. 
That's why a 12v battery supplying a circuit with these leads will have 11v at the circuit. 
Note:
Turn off the equipment before making any continuity tests. The presence of even a small voltage (from an electrolytic) can give a false reading.
You can determine the resistance of a lead very accurately by taking the example above and applying it to your circuit. 
If the battery is 12.6v and the voltage across the circuit is 10v, when the current is 2.6 amps, the resistance of the "leads" is 12.6 - 10 = 2.6 R=V/I = 2.6/2.6 = 1ohm. By making the lead shorter or using thicker wire, the resistance will be less and the voltage on the project will increase. 
When taking readings in a circuit that has a number of diodes built-into IC's (Integrated Circuits) and transistors, some Continuity Testers will beep and give a false reading. 
The following circuit has the advantage of providing a beep when a short-circuit is detected but does not detect the small voltage drop across a diode. This is ideal when testing logic circuits as it is quick and you can listen for the beep while concentrating on the probe. Using a multimeter is much slower.

Fuse (Presented as letter F or PF)

Fuses and PTCs – devices which are generally used to limit large inrushes of current – each have their own unique symbol .Testing Fuse just using Continuity test ,if both terminal loosing their continuity it is mean Fuse is broken.

Node Voltage

Sometimes – on really busy schematics especially – you can assign special symbols to node voltages. You can connect devices to these one-terminal symbols, and it’ll be tied directly to 5V, 3.3V, VCC, or GND (ground). Positive voltage nodes are usually indicated by an arrow pointing up, while ground nodes usually involve one to three flat lines (or sometimes a down-pointing arrow or triangle).

 Voltage Regulators (Presented as letter U or PU)

Some of the more common integrated circuits do get a unique circuit symbol. You’ll usually see operation amplifiers laid out like below, with 5 total terminals: a non-inverting input (+), inverting input (-), output, and two power inputs.
Often, there will be two op amps built into one IC package requiring only one pin for power and one for ground, which is why the one on the right only has three pins.

Crystal Clock Oscilator (Presented as letter Y or X)

Crystals or resonators are usually a critical part of microcontroller circuits. They help provide a clock signal. Crystal symbols usually have two terminals, while resonators, which add two capacitors to the crystal, usually have three terminals.

Connectors (Present as letter J,JP,CN and others)

Whether it’s for providing power, or sending out information, connectors are a requirement on most circuits.

Inductors (Present as letter L or PL)

Inductors are usually represented by either a series of curved bumps, or loopy coils. International symbols may just define an inductor as a filled-in rectangle.

Inductor allways present in the end of any voltage supply on Laptop motherboard circuit,we could identified any Voltage rail on it to check wether Voltage need are present .Processor voltage supply could be measure at the Vccore inductors ,they always placed near the processor socket ,Southbridge inductor will located on soutbridge chip ,memory inductor will placed near memory socket.if one of pin inductor having voltage present but the other one not it mean inductor damage .this component should passing the voltage from input pin to output pin to supply the voltage needs.

NOTE: TESTING ANY CONTINUITY SHOULD REMOVED ADAPTER SUPPLY BEFORE DOING A TEST.

Mosfet Transistors (Present as letter Q or PQ)

MOSFETs have three terminals, but this time they’re n
amed source (S), drain (D), and gate (G). And again, there are two different versions of the symbol, depending on whether you’ve got an n-channel or p-channel MOSFET. There are a number of commonly used symbols for each of the MOSFET types: 
The arrow in the middle of the symbol (called the bulk) defines whether the MOSFET is n-channel or p-channel. If the arrow is pointing in means it’s a n-channel MOSFET, and if it’s pointing out it’s a p-channel. Remember: “n is in” (kind of the opposite of the NPN mnemonic).

P channel mosfet will find on ADP+ main lone circuit .They shoud passing away the voltage from source (input) to drain output at same vallue .if they not check gate vallue as a triger to release input voltage to the output drain.

This N channel usualy use for swicthing regulator,Source input must ready in the very begining before gate open .Gate will giving a triger to release the voltage to the output drain as much as Gate vallue voltage.

N channel mosfet logic lo w (vi) that mean mosfet not close circuit between the drain and source ... v_out you got vdd voltage via resistance . (Hi) ...when you apply vi = Hi in N-Channel mosfet <--- mean drain to source connected (close circuit) in this case you got v_out <<<--- source low you can got at v_out ...same way in P-channel but gate work reverse as n-channel mosfet work.
Transistors can be used for various purposes. One of them is used as an amplifier. Widely used on circuit as a current amplifier, a voltage amplifier and power amplifier. The function of semiconductor components can be identified in the circuit by way of installation of ground and input capture / output.

GATE amplifier (grounded-GATE)

As the Common Base foot GATE transistor in groundkan, then input the insert into and output SOURCE DRAIN taken on foot. GATE amplifier has the character as voltage amplifier.

Upholstery caracteristic Gate
Their input and output isolation so high that smaller Feedback
Suitable as a Pre-Amp because it has a high input impedance which can amplify small signals
Can be used as high-frequency amplifier can be used as a buffer or buffer

SOURCE amplifier

As a transistor amplifier  SOURCE foot on ground, then input insert into GATE and DRAIN output take on foot. as well as having the character as an amplifier of this series . SOURCE on the ground, and the GATE as input, and output is DRAIN.

Caracteristic amplifier Source

Signal output is 180 degrees different phase or reverse phase by 180 degrees with respect to the input signal.
It is possible for oscillation due to feedback or positive feedback, so as to prevent it often mounted negative feedback.
Often used as a signal amplifier microcontroler
Having a strengthening stability depends on the stability is low because the temperature and bias use as transistor DRAIN amplifier

Resistors (Present as letter R or PR)

The most fundamental of circuit components and symbols! Resistors on a schematic are usually represented by a few zig-zag lines, with two terminals extending outward. Schematics using international symbols may instead use a featureless rectangle, instead of the squiggles.

Switches (Present as letter S,SW and other)

Switches exist in many different forms. The most basic switch, a single-pole/single-throw (SPST), is two terminals with a half-connected line representing the actuator (the part that connects the terminals together).

Cmos Battery symbol

SMPS 3V_5V regulator system symbol (Present as letter U or PU)

Vccore power regulator symbol (Present as letter U or PU)

DC Jack connector symbol

Battery Pack connector symbol

Sata Hard disk connector symbol

Sata Optical drive symbol

Electronic Langguage

Understand the electronic language. There will be a variety of schematic symbols on the schematic that represent real world devices and wires. A basic understanding of these symbols is required to read a schematic.

Understand ground. Ground is represented by either a triangle pointing down or a set of parallel lines that become shorter as they appear below each other, in effect representing the inner area of the triangle pointing down. Ground is a common reference point that schematics use to show the overall unity of the various functions of the circuit. It does not refer to the actual ground of the earth.

A line represents a wire. Wires are used to connect the devices together. All points along the wire are identical and connected. Wires may cross each other on a schematic, but that does not necessarily mean that they connect. If they do not connect, one will be shown looping around the other in a semicircle. If they do connect, they will cross and a dot will be seen at the point where the lines cross.
Resistor is represented by a zigzag shape. Resistors act to impede the flow of the circuit to an extent determined by the resistance value used. They are used to scale and shape the signal.
The voltage drop across a resistor is equal to the current flowing through it times the value of the resistor (V=IR). This allows the classic use of resistor to divide down a voltage. If a voltage source is applied to two consecutive resistors of the same value, the voltage created at the point between the two resistors will be half of the original voltage applied.
Capacitors are represented by two parallel lines. Capacitors are used to condition rapidly changing signals, as opposed to the static or slower changing signals that are conditioned by resistors. The traditional use of capacitors in modern circuits is to draw noise, which is inherently a rapidly changing signal, away from the signal of interest and drain it away to ground.
The non standard symbols will be of a geometric shape, usually a rectangle, with a device indicator number in or beside the shape. The indicator number should be Uxx. Wherever a wire contacts the device, there will be a number indicated at the connection point. This number is the pin number of the device.

Electronic devices are normally assembled on printed circuit boards (PCBs) that mechanically support and electrically interconnect parts by using conductive traces, etched from copper sheets laminated onto an isolating substrate. The size of the traces is calculated based on their current-carrying capacity and acceptable impedance.
Make sure printed circuit board code number recognized to get same number of schematic diagram applied .

Current and Voltage

Electric current is the number of electrons (electric charge) that flows through a point in the electrical circuit per unit time. electric current flows from the positive pole to the negative pole, it is because the positive pole has a higher potential than the negative pole.

Voltage is a potential difference that difference is the number of electrons in a material. On the one hand there are electrons accumulate material while on the other side there is the number of electrons were slightly. This is due to the magnetic force affecting the material. In other words, the material into an electric voltage. The magnitude of the effect of the electric current depends on the magnitude of the difference of electrons collected in a material (potential difference) .

Schematics are the maps that provide guidance on the assembly and functioning of an electronic circuit. Without a schematic, only an undocumented mass of devices and wires would be presented to the user or designer. A schematic allows the user or designer to understand the circuit function and become familiar with how the desired effect of the electronic circuit is achieved.

 When we open the schematic , we will find the contents of the index circuit components, directions and connections between components, the manufacturer's standard voltage, power sequences, voltage rail to enhance their production and new problems are known at the time the product is already in the market.
At the beginning of the index page describes the details of the pages on the circuit that allows us to look for problem areas happened on the motherboard.

Names and Values

Values help define exactly what a component is. For schematic components like resistors, capacitors, and inductors the value tells us how many ohms, farads, or henries they have. For other components, like integrated circuits, the value may just be the name of the chip. Crystals might list their oscillating frequency as their value. Basically, the value of a schematic component calls out its most important characteristic.
Component names are usually a combination of one or two letters and a number. The letter part of the name identifies the type of component – R’s for resistors, C’s for capacitors, U’s for integrated circuits, etc. Each component name on a schematic should be unique; if you have multiple resistors in a circuit, for example, they should be named R1, R2, R3, etc. Component names help us reference specific points in schematics.
The prefixes of names are pretty well standardized. For some components, like resistors, the prefix is just the first letter of the component. Other name prefixes are not so literal; inductors, for example, are L’s (because current has already taken I [but it starts with a C…electronics is a silly place]). Here’s a quick table of common components and their name prefixes:

Identify Blocks

Truly expansive schematics should be split into functional blocks. There might be a section for power input and voltage regulation, or a microcontroller section, or a section devoted to connectors. Try recognizing which sections are which, and following the flow of circuit from input to output. Really good schematic designers might even lay the circuit out like a book, inputs on the left side, outputs on the right.

The composition of the layout of the diagram are arranged horizontally, so it will look a little different to that of the actual motherboard on hand .dimension can be referred to in the diagram components side by side, it was in fact located on the opposite, or being away from that we need pay attention to the same component layout code in the diagram and the motherboard in order to understand the components in question by the diagram
Here we will look at the illustrations, how do I find the layout of the components based on the location code, symbols, components and circuit line either as a power supply or data interface.

Sample:

Toshiba L745 Motherboard code TE5 can't switch on problem ,19V_5V and 3V are present NBSWON# signal on Power switch button connector (CN2) Missing ,check EC Bios power 3.3V on pin 8,7 and 3 Present.reprogram EC bios (U13) 512KB NBSWON# on SW coming for 3.3V but still same problem .tracing NBSWON# directly to Nuvoton (EC)pin 96 ,3.3V present , short NBSWON# to the ground 3.3V become 0V and back to 3.3V (switch signal response).To ensure EC firmware, bios ic and EC good i got 3.3 V on RSMRST# pin 75 NPCE 791LAODX .and than check DNBSWON# 3.3V also present but no SusC# return signal from SB to EC .trace SUSC# continuity from SB to EC they where connected .no PLT_RST# signal .to ensure this cause Main bios Firmware, reprogram Main Bios U6 (4mb) with tested firmware still got no PLT_RST# signal .Checking Caps on HM55 (SB) chip all pin shorted to ground ,Take off HM 55 and shorted gone .Reball HM55 and put them back carefully using CF 260 (BGA melted on 245'C) let them cool for half an hour than check SUSC# signal present .Problem solved.

If the problem refers to the power module then we can assume that the ic / chip related to power problems. there are a lot of ic / chips on the motherboard power supply support ,that is also called the power module.

 Knowing the circuit groups and chip power source supply ,we have narrowed down the search area problematic components. voltage and resistance information mentioned .
components in the page described the relationship between components and voltage standards requested by the motherboard to run normally. do measurements on components, if we find there is one component that does not emit voltage or does not meet the demand in the schema, then we assume that the component is faulty / short or broken. do the replacement and re-do the measurement.