There are many types of resistors used in the motherboard, which are divided into:
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Ordinary resistance is the smallest resistance on the main board. The shape is a small square with a flat ink. The resistance of the chip resistor is generally represented by three digits. After the three digits, "0" is added (the unit is Ω). If there is a decimal point in the resistance, it is represented by "R" and takes up a valid number.
For example, the resistance of the chip resistor labeled "123" is 12*104 = 120000 Ω = 120 KΩ.
The chip resistor on the motherboard is sometimes not in the form of a number + letter without marking its resistance value. The first two digits are numbers and every three digits are letters. The resistance value represented by this method is different from the identification method represented by the previous method - its first two digits are just a generation of horses, and do not represent the actual resistance value, and the code representation is valid. The number varies with the package form. The chip resistor labeled "0" or "000" has a resistance of 0 Ω. This resistor is actually a jumper. In some motherboard circuits, a chip resistor with a resistance of 0 Ω is not commonly used as a fuse resistor or as an EMI EMC resistor.
Exclusion is also called network resistance or network resistance. Exclusion is a composite resistor that combines multiple resistors together and combines them.
The types of exclusion in the motherboard are available in both in-line and on-chip packages. The chip package is available in 8-pin and 10-pin versions.
Under normal circumstances, chip exclusion is not polar, but some types of SMD exclusion, due to different internal circuit connections, in practical applications, you need to pay attention to polarity.
Knowledge points: The resistance of the internal resistors used on the main board is the same. If one of the resistors is detected to be different from the other resistors, the entire resistor is replaced by an error.
The fuse resistor is also known as the fuse resistor. The fuse resistor plays the dual role of the fuse and the resistor in the circuit. It is mainly used in the power supply circuit. The resistance of the fuse resistor is generally small (several ohms to tens of ohms) and the power is also small. (1/8--1w). Commonly used on the motherboard are patch insurance resistors and high-power in-line fuse resistors. The color of the patch fuse resistor is usually green or gray, and the surface is marked with a white number "000" or rated current.
The high-power in-line fuses commonly used on the motherboard are generally marked with a color ring to indicate its rated resistance and rated current. The resistance of different high-color in-line fuse resistors is not represented by different colors.
High-power in-line fuse resistors with different color rings
Color resistance (Ω) power (W) current (A)
Black 10 1/4 3.0
Red 2.2 1/4 3.5
White 1 1/4 2.8
The thermistor is on the main board. The thermistor is mainly used to test the temperature of the CPU and the internal temperature of the chassis. Usually, it is in the socket of the socket or the edge of the motherboard. Some shapes are like chip resistors, and some shapes are like a "small ball". Generally used in a vertical package.
The identification of the resistance is in the schematic diagram of the main board circuit. The resistance is usually expressed in uppercase English and its mother "R". The insurance resistor is usually capitalized in English letters "RX" or "RF", "F", "FUSE", "XD", "FS". "To show, the exclusion is generally indicated by the capital letter "RN", and the thermistor is generally indicated by the capital letters "RM" and "JT".
The two ends of the series/parallel circuit resistance of the resistor are connected end to end in series, forming a closed loop, called a series circuit. In the series circuit, the total resistance of the resistor is the sum of the resistance values: R total = R1 + R2 . In a series circuit, the current flowing through each resistor is the same.
The two end points of the resistor are connected together in a side-by-side manner to form a closed loop, called a parallel circuit. In the parallel circuit, the voltage across each resistor is the same. In the parallel circuit, the reciprocal of the total resistance of the resistor is The sum of the reciprocals of the resistance values ​​of the resistors, that is, R = (R1 * R2).
In the practical application circuit, there are both a series of resistors and a parallel connection of resistors. Such a circuit is called a series-parallel circuit of resistors. In the series-parallel circuit, the portion in which the resistors are connected in series has the characteristics of a series circuit, and the portions in which the resistors are connected in parallel have the characteristics of a parallel circuit.
Capacitors Capacitors have a certain ability to store charge and can be charged or discharged. Capacitors can only pass AC power and cannot pass DC power. They have the characteristics of DC, AC, high frequency and low frequency. They are filtered, coupled, bypassed in the circuit, or composed of RC timing circuits and inductors. Resonant circuits, therefore, often oscillating circuits, tuning circuits, filtering and bypass circuits, and coupling circuits.
On the motherboard circuit, the capacitor is generally used in the power supply circuit part, mainly for filtering. Capacitors are divided into polar capacitors and non-polar capacitors. The chip ceramic capacitors are non-polar, and the electrolytic capacitors are sexual and cannot be connected incorrectly.
The chip ceramic capacitor is the most widely used capacitor in the motherboard. This capacitor mainly functions as bypass, high frequency filtering and oscillation in the motherboard circuit, generally beige or light gray, in the motherboard circuit for convenience. Assembly, usually also uses a capacitor with a plurality of capacitors mounted together. The commonly used capacitors on the motherboard have 8 pins, and there are 4 capacitors with the same capacity inside. The internal circuit is composed in the same way as the 8P4R.
Aluminum Electrolytic Capacitors In the main board circuit, aluminum electrolytic capacitors are mainly used in the filter circuit of the rectifier circuit, and in the circuit of the power supply decoupling and bypass. On the capacitor housing, a black marker strip is usually drawn at one end of the negative lead wire, and the new aluminum electrolytic capacitor has a long leg for the positive pole.
When the electrolytic capacitor is reversed in polarity during use, the current flowing through it is too large, causing its thermal breakdown to break down. The gas generated by the temperature rise may cause the capacitor casing to burst.
Tantalum Electrolytic Capacitor It uses metal but does the positive electrode. It is made into a negative electrode with a solution such as dilute acid. The shape is cuboid and the color is usually yellow or black. The aluminum electrolytic capacitor is usually printed with a 'CA' mark on the outer casing, but the symbol in the circuit is the same as the symbol of its electrolytic capacitor. The capacity and withstand voltage of tantalum electrolytic capacitors are usually directly marked on the surface of the capacitor. Some omits the unit "UF" of the capacity and the unit "V" of the withstand voltage value; the value of the withstand voltage is usually 50V. On the motherboard, there are some tantalum electrolytic capacitors with three digits.
Solid Electrolytic Capacitor It is a kind of polar electrolysis. The solid electrolytic capacitor has a rated voltage of 2-35V, a vacancy of 1-2700UF, and an equivalent series resistance of up to MΩ, which is widely used in power supply filter circuits in new motherboards.
The identification of the capacitor is in the circuit. The capacitance is generally indicated by the capital letter "C" plus a number. On some motherboards, the capacitor character "C" is preceded by a letter indicating the circuit and location of the capacitor, such as "AC01" The first capacitor in the audio.
The capacitance of the series/parallel circuit capacitors in parallel is equivalent to the total area of ​​the respective parallel capacitors. Therefore, after multiple external capacitors are connected in parallel, the total capacitance is the sum of the capacitances of the parallel capacitors, ie C=C1+C2+. C3+CN.
When the two capacitors are connected in parallel, the loss resistance R of the entire capacitor is the parallel connection of the two capacitors, and the actual value of the loss resistor R is small, so that the loss of the combined capacitor in the high-capacity circuit is small. Can meet the needs of the oscillation circuit.
In some cases, the capacitors can also be used in series. After the capacitors are used in series, the distance between the metal plates is equivalent to the sum of the components of the series capacitors, and the total capacitance is smaller than the capacity of any one of the series circuits. The reciprocal of the total series capacitance is the sum of the reciprocal of each capacitance.
After the capacitors are connected in series, a partial voltage is generated, and the voltage dividing ratio is the reciprocal ratio of the capacitance. When the two capacitors are in series, the loss resistance of the two capacitors is also in the series closed state, so the entire capacitor is equal. The efficiency loss resistance becomes large, which may cause the consumption value to become large.
Inductor The main function of the inductor is to convert the electrical energy into magnetic energy and store it. Therefore, it can also be said that it is a component that stores magnetic energy. The power plant sense is based on the principle of electromagnetic induction. When a current flows through a wire, an electromagnetic field is generated around the wire, and the electromagnetic field electromagnetically induces a wire in the electromagnetic field, usually a coil wound by a single wire. There will be a self-inductive effect; a coil made of one or more wires will have a mutual inductance.
The characteristics of the inductor are opposite to those of the capacitor. It has the characteristic of preventing the passage of alternating current and allowing direct current to pass. When the DC signal passes through the coil, the resistance is the resistance of the wire itself, and the voltage drop is small. When the AC signal passes through the coil, the self-induced electromotive force will be generated at both ends of the coil, and the direction of the self-induced electromotive force is opposite to the direction of the external voltage, which hinders the communication. Pass, so the characteristic of the inductor is DC resistance AC, the higher the frequency of the signal, the greater the impedance of the coil.
When the magnitude or direction of the current flowing through the inductor changes, the inductor generates a back electromotive force to block the current change. Therefore, the current across the inductor cannot be abrupt.
The role of the inductor in the main board is mainly filtering (power supply filtering), energy storage (DC-DC conversion), and people also use the characteristics of the inductor to manufacture electromagnetic components such as choke, transformer, and relay.
Inductor Identification There are two kinds of inductors in the motherboard: chip inductor and wire wound inductor. The chip inductor is divided into two types: small power inductor and high power inductor (wire wound film inductor). Common patch low power inductor color is gray black, inductance range is 0. 1-200UF, rated current is up to 100MA, with magnetic circuit closure, less magnetic flux leakage, no interference with surrounding components, less susceptible to interference and high reliability. To the advantage. It is mainly used in the filter and anti-interference circuit in the motherboard.
Wirewound inductors are further divided into color ring inductors and core inductors. The color ring is similar to a normal color ring resistor, and three or four color rings are usually used to mark the inductance.
The inductance of the inductance of the inductance is usually called the color ring inductance or the color code inductance. The inductance identification method is as follows: the color ring close to one end of the inductor body is the first ring, and the original body of the inductor body is exposed. The other end is the last ring. The first color ring is a tens digit, the second color ring is a single digit, the third color ring is a multiple that should be multiplied (in UH), and the fourth color ring is an error color ring. The values ​​represented by the colors are shown in the table:
The values ​​represented by the various colors
Color first color ring second color ring third color ring (multiple) fourth color ring (error)
Black 0 0 1 ±20%
Brown 1 1 10 ±1%
Red 2 2 100 ±2%
Orange 3 3 1000 ±3%
Yellow 4 4 10000 ±4%
Green 5 5 100000
Blue 6 6 1000000
Purple 7 7 10000000
Gray 8 8 100000000
White 9 9 1000000000
Gold 0.1 ± 5%
Silver 0.01 ±10%
The shape of the color ring inductor color ring resistor is similar, so pay attention to distinguish when using it. Under normal circumstances, the shape of the color ring inductor is mostly short and thick, and the color ring resistance is usually slender.
The magnetic core is composed of a coil and a magnetic core, and mainly functions as an energy storage device. It is usually applied to a DC_DC DC voltage conversion circuit (CPU power supply circuit) in the main board. If the color of the coil in the wire wound inductor is golden yellow, it is normal. Enameled wire, when the temperature of the enameled wire is high, the surface insulation is easily broken down, falling off, causing short circuit, and the inductance of the coil is reduced. The coil surface of the high-end motherboard is coated with a high-temperature insulator, and the color is usually dark red.
Crystal Oscillator is an electronic device used to stabilize frequency and select frequency.
Crystal oscillator identification clock crystal: The crystal oscillator is connected to the clock generation integrated circuit at a frequency of 14.318MHZ. After the crystal oscillator is broken, the motherboard will not be able to start the fault. During normal operation, the voltage between the two pins is 1-1. 6V.
Real-time crystal oscillator: This crystal oscillator is connected to the south bridge chip at a frequency of 32.768MHZ. After the crystal oscillator is damaged, it will cause inaccurate time or failure to start. In normal operation, the voltage between the two pins is about 0. 5V. .
Sound card crystal: This crystal is connected to the sound card chip, the frequency is 24.568MHZ, which will cause sound deterioration and silent failure. Normally, the voltage between the two pins is 1.1-2.1V.
NIC crystal oscillator: This crystal oscillator is connected to the NIC chip. The frequency is 25.000MHZ. After the crystal oscillator is damaged, the NIC will not work. In normal operation, the voltage between the two pins is 1.1-2.1V.
Indicates the letters "X", "Y", "G", "Z".
Diodes have two pins, positive and negative. The positive electrode is called anode A, and the negative electrode is called cathode K, so it is called diode. The diode has a unidirectional conductivity characteristic, that is, current can only flow from the anode to the cathode, but not from the cathode to the anode. When the current is from the anode to the cathode, the diode is in a short-circuited state, and there is no resistance, that is, there is no obstacle to the flow of current. Conversely, when the current is attempting to flow from the cathode to the anode, the diode is in an open-circuit state with an infinite resistance, so that the current cannot flow.
Diodes in the motherboard circuit, mainly have switches, rectification, isolation, voltage regulation and so on.
Classification of diodes in the motherboard
Switching Diodes The main types of switching diodes on the main board are SSM4148 (SMD Switching Diode), 1N4148 (In-Line Switching Diode), and so on. This type of diode is mainly used for functions such as isolation diodes and electronic switches.
Schottky diode Schottky diodes are usually used in high frequency, high current, low voltage rectifier circuits. The front special diodes in the motherboard have small power charging and in-line type, low power chip type, low power double diode, large Power double diode and other types.
The commonly used low power in-line Schottky diode model is 1N. 5817.
Small power chip diodes mainly include SS12, SS3484, GW435817, BAR43, RB731U and other models.
A common model for low power dual Schottky diodes is the LD3.
High-power dual Schottky diodes are commonly used in high-current rectifier circuits. Commonly used models are SBG1035, SBG1040CT, and BYV1035.
The biggest difference between a Zener diode and a general diode is that the diode is destroyed after reverse breakdown, and the Zener diode does not exceed the maximum allowable operating current, so it will not be destroyed. In practical applications, the Zener diode It is working in the reverse breakdown state.
The Zener diode is classified according to the breakdown voltage. The voltage regulation value is the breakdown voltage value. The Zener diode is mainly used for the voltage reference in the regulated power supply, or used as a protection diode in the overvoltage protection circuit. The voltage diodes can be connected in series to a higher regulated value.
The Zener diode used in the motherboard circuit is usually a glass-packed Zener diode with a color ring labeled with a constant voltage value, usually called a color ring stabilized diode.
Identification of the diode The negative pole of the diode is usually marked with a color ring on the surface. In the circuit diagram of the computer, the common diode is often represented by the letter "VD" or "D".
In the main board circuit, the circuit symbols of the switching diode and the Schottky diode are the same as those of the ordinary diode circuit.
The color of the glass tube wall of the color-coded diode is yellowish green or orange. The voltage is marked with two or three color rings, and the first color ring is close to the service extreme.
The color of the color represented by the color of the color circle represents the numerical value representing the value of brown 1 blue 6
Red 2 purple 7
Orange 3 ash 9
Yellow 4 white 9
Green 5 Black 0 Transistor has current amplification and switching function, is the evaluation device of electronic circuit. Transistor has two types of PNP tube and NPN tube. The difference between them is that the current direction is different when working. In the main board circuit, the NPN type triode is used more. The three pins of the transistor are the emitter (E pole) and the base (B pole) and the collector (C pole).
Transistor identification triodes commonly used letters "Q", "V", "VT" plus numbers, according to the structure, transistors can be divided into two types of PNP type and NPN type, on the circuit graphic symbol, the emitter of two types of transistors The arrows (representing the direction of the collector collector current) are different. The PNP tubular crystal aviation emitter arrow is facing inward, and the emitter arrow in the NPN transistor is facing outward.
The type of triode type is usually printed on the surface of the tube. In some plastic packaged triodes, because of the small size of the tube surface, for ease of printing, many models usually remove the common prefix and only print the back digital model.
The working state of the triode In the motherboard circuit, the amplification and switching functions of the triode are mainly used.
The triode has a current amplification effect, which is essentially that the triode can control the large change of the collector current with a small amount of change in the base current, which is the most basic and most important characteristic of the triode. The current amplification number is a fixed value for a triode, but there will be some changes as the base current changes as the triode operates.
The main function of the triode is to amplify the current signal. When a small amount of current flows between the base and the emitter, it will trigger a large current from the collector to the emitter. The function of the amplifier is basically to amplify a small electrical signal (which can be voltage, current or power) at the input to a large electrical signal (voltage, current or power) at the output.
Substitution of Transistor When replacing a triode, first consider the parameters of the current amplification factor, dissipated power, frequency characteristics, collector maximum current, and maximum reverse voltage of the triode.
When replacing the triode, the limit parameter of the new transistor should be equal to the original triode; the triode with good performance can replace the triode with poor performance.
Before replacing the triode in the motherboard, it is best to figure out the specific role of the triode. For general signal amplification, the switching transistor can be replaced by 2N3904 (NPN) and 2N3906 (PNP) (only for motherboard maintenance); for triode in regulated power supply, use 2SB772 (PNP), 2SD1802 (NPN) Replacement can meet the requirements (only for motherboard repair), pay attention to not confuse the same packaged FET and triode in the replacement.
The FET tube and the triode can achieve signal control and amplification, but because of their different construction and working principle, the difference between the two is very large. The type of FET in the motherboard is currently the most widely used in the motherboard. It is an insulated gate field effect transistor, referred to as MOSFET.
The control pin of the FET is the gate or the gate (G pole), the corresponding FET pin is called the source (S pole); the third pin corresponding to the FET is called the drain (D pole) ).
The corresponding relationship between the FET and the triode is that the gate (gate) corresponds to the base, the source corresponds to the emitter, and the drain corresponds to the collector. The field effect tube in the main board has the P channel and the N path according to the polarity. The P channel field effect tube works in the same way as the N channel field effect tube except that the conductive carriers are different, so the supply voltage The polarity is different, just like the generalized triode is divided into NPN and PNP.
Commonly used FETs on the motherboard include SOT-23, SOT-223, SO-8, TO-251, TO-252 (TO-263) and other chip package types.
The identification of the FET is in the computer circuit. The FETs are often represented by the letters "V", "Q", and "VT". The position of the FET pins depends on the type and function of the FET. Proper use of FETs must first identify each electrode of the FET. For the use of the patch FET in the motherboard, the pin arrangement from left to right is basically G, D, S (heat sink connected to D pole), the FET used in the motherboard, in which the DS pole is added. Protect the diode to protect the tube from static breakdown.
In the maintenance work of the field effect tube, it is absolutely impossible to replace the P-channel field effect tube with the N-channel field effect tube, and vice versa. In the actual motherboard maintenance, there must be a volume and phase phase. , N-channel replacement N-channel, P-channel replacement P-channel, can meet the general maintenance requirements (only for motherboard maintenance).
Regulators On the motherboard, in addition to the Zener diodes, there are three-terminal regulators, three-terminal reference regulators and other voltage regulators.
Three-terminal regulators Three-terminal regulators commonly found on motherboards are available in TO-92, SO-223, and TO-252 packages.
The TO-92 package includes MC78L05 (output current 100MA, positive voltage regulator with 5V output voltage), MC79L05 (output current 100MA, negative voltage regulator with output voltage of 5V). Mainly used to power circuits such as sound cards and network card chips.
The owners of the SO-223 package are LM1117, KA1117, EZ1117, H1117, WSL1117-2. 5, AMS1117, APL1117, LTC1117 and other models. Mainly used to power Northbridge, Southbridge, memory, AGP graphics, clock and other circuits. A positive three-terminal regulator with an output current of 1A can be directly replaced by the same output voltage.
The three-terminal regulators in the TO-252 package are available in LX8384, L1084, LD1084, L1581 and other models. Mainly used to supply power to circuits such as memory and north bridge.
The three-terminal regulator is indicated on the motherboard by the letters "Q" or "U" or "VR". In the case of power-on, turn the multimeter to 20V voltage, the black meter is connected to the ground, and the red meter is connected to the voltage output of the three-terminal regulator (such as the heat sink of the three-terminal regulator). If it meets the requirements, it is normal.
Three-terminal reference regulator The commonly used three-terminal reference regulator in the motherboard is the TL431. It is 2. 5 -36V adjustable precision shunt regulator, can be directly replaced with KA431, TLV431A, uA431, LM431.
In the main board, the TL431 mainly performs the comparison amplification task between the sampling voltage and the reference voltage.
The TL431, KA431, and TLV431 are available in three package types. The three electrodes are the reference electrode R, the anode A, and the cathode K, respectively. There is a precision reference voltage source that does not ignore the old 2. 5V. By using two external resistors, a stable voltage of 2.5-36V can be obtained. Usually expressed by "Q", "U", "VR". The TL431 contains a 2.5V reference internally, so when the output feedback is introduced at the REF terminal, the device can control the output voltage by shunting a wide range from cathode to anode.
The operational amplifier is mainly used as a voltage comparator in the main circuit circuit. It is usually used in the memory supply circuit, the north bridge power supply circuit, and the PCI graphics card power supply circuit. The commonly used operational amplifier models in the main board include LM358, TL072, LM393, and LM324. Although the pin functions of the LM358, TL072, and LM393 are identical, they cannot be replaced directly during maintenance due to their different characteristics.
Logic Gates Circuits that can be logically operated are called logic circuits or digital circuits. The logic gates commonly used in motherboards are AND gates, OR gates, NAND gates, NOR gates, buffers, flip-flops, and bus transceivers. In some new motherboards, 8-bit row input/parallel output right shift is also used. register.
Knowledge points: When analyzing the gate circuit, the two names of high and low are often used.
Low level: refers to a voltage lower than 0.8V. Use the letter "L" or the number "0" to indicate a high level: a voltage higher than 2. 5V. Use the letter "H" or the number "1" to indicate that the motherboard is commonly used. The logic gates are the 74 series of integrated circuits, which are divided into TTL gates and CMOS series circuits. TTL ICs can be broadly classified into six categories: 74xx (standard), 74LSxx (low-power Schottky), 74ASxx (Schottky) 74ALSxx (advanced low-power Schottky), 74ASxx (Advanced Schottky) ), 74Fxx (high speed); CMOS integrated circuits are mainly 74HCxx, 74HCTxx, 74HCUxx three categories.
The motherboard commonly used logic gate circuit mainly has the following models.
And gates: 7408, 7409, 7411, 7421.
Or Gate: 7432.
Non-gate: 74HCT14, 74LS14, 7405, 7406.
NAND gate: 74F00.
NOR gates: 7402, 7410, 74F02.
Buffer: 74F125, 74F244, 7407.
Trigger: 74273, 74HCT74, CD4013, 74LS132.
Bus transceiver: 74245.
Other integrated circuit north bridge chip south bridge chip clock chip
I/O chip power management chip sound card chip network card chip BIOS chip
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