Computer motherboard does not trigger.

observe the main chip, PCB board, power IC and each slot.

observe whether the main chip has obvious burning, scorching and explosion.

check each slot for short circuit.

touch method: (power on for a period of time): touch each chip, IC, etc. of the motherboard to see if it is overheated or too cold. Overheating: ① internal short circuit, ② high power supply voltage. Too cold: ① open circuit, ② no power supply, ③ unsatisfactory working conditions.

resistance method:

isa: the first eight d lines are the same to the ground R ..

in the early stage, 2 A lines have the same R to the ground (some boards are segmented).

the last 7 lines a are the same to the ground R ..

the last eight d lines are the same to the ground.

they are generally not more than 15 Ω, and the difference between IRQ, DRQ and DACK is not more than 25 Ω.

PCI:

32 AD lines have the same ground R, and it is normal that some motherboards may have one line that is several tens Ω smaller than the other 31 lines.

AGP:

32 AD lines are the same to ground R

Waveform method:

Important test points: reset, SCLK, OSC, BE-BE7 (signals that allow data address to work) A3 (signs that reflect the south bridge to work), CS, OE.

wave locking method: for motherboards below 586, P Ⅱ and P Ⅲ are not allowed, otherwise the CPU will be burned).

connect a23-VCC on the CPU base, and compare the waveforms of test points. If there is any inconsistency, find the fault point by combining the resistance method. (Premise: the three working conditions of CPU are met, and there are some waves on ISA and PCI slots).

digital card method: (reflecting the process of BIOS self-check)

FF and CPU do not work or the working conditions are not satisfied, and the motherboard has serious faults (mainly check the three working conditions of CPU, BIOS and main chip).

the memory control part of CI and C6 memory slots (memory bars) (mainly checking memory power supply, north bridge, memory slots, clock failure, etc.).

31 should be displayed. If it is not displayed, check the AD line on PCI. There may be an open circuit or a short circuit.

3d, 42

4e press f1

41 BIOS, which is more likely. COMS circuit RTC

C1→5→C1→5 (cycle)

1, memory slot. 2, CPU power supply. 3, I/O chip. 4，KBC。

U1→5→U1→5 (cycle)

VII. Logical reasoning:

It is mainly used to infer the quality of TTL, 74 series and gate circuits.

not gate: inverter or gate: adder and gate: multiplier

8. replacement method: when the specific parts cannot be determined, replace the suspected parts with good parts. This method is widely used in practice. The eight-character policy of maintenance: department, level, road, point, road, management, transportation and school.

Common failures

Common failures of the motherboard:

Power failure 2, bus failure 3, critical failure 4, non-critical failure

Cannot trigger:

Real-time clock 32768 is broken, and peripheral resistance and capacitance of the generator are broken.

power supply triodes

74f and 74f14 and their peripheral resistors, diodes and triodes.

battery failure.

south bridge.

I/o chip.

the purple and green lines of p>ATX power supply are connected. (triggered part)

(not turned on: 1. cpu address line A3, there must be a wave, if there is no wave, the south bridge will be broken.

2. If the data lines DP1 and DP3 do not have this signal, but there is one around them, the south bridge is broken.

if there is a wave here, but there is no wave in the BIOS, the BIOS is bad or the south bridge.

3. be-be7, if there is no wave at all, the north bridge will be broken (there should be

a wave without CPU).

4. U1-UB is not turned on. On the premise that lines A and D on BE-BE7 and BIOS are normal, measure lines A and D on CPU to judge the working conditions of the south and north bridges. At this time, it is very likely that the south bridge is broken. )

can't remember:

battery.

32768 crystal oscillator

RTC (south bridge).

CMOS circuit

automatic shutdown:

peripheral components of south bridge.

74, 74l4 and their peripheral components

the power of host power supply (ATX) is insufficient.

the power supply on the motherboard is indirectly short-circuited to ground.

power on the motherboard (or smoke)

power supply. (+12 power supply and +5V short circuit to ground, mainly power supply transistor and electrolytic capacitor)

COM port control chip.

the resistance near the com port.

slot short circuit or artificial short circuit (tin slag)

maintenance without starting the machine:

first check three conditions: VCC, clk and reset. (mainly CPU)

On the premise that the three conditions are normal, the BIOS does have 22 pins of CS and 24 pins of OE.

judge the quality of south bridge, north bridge and I/O chip by measuring the R-ground of AGP, PCI, ISA, SIMM or DIMM of CPU base.

power failure

① there are three groups of power supplies on the board of p ⅱ and above: 1, 3.3V 2, 1.8V-2.2V 3 and 1.5v.

1 and 3.3V generally supply power for each IC, and the voltage is directly provided by the orange line of ATX power supply.

2, 1.8V-2.2V, output by two field effect transistors and power IC(TL494CN).

3 and 1.5V are output by a field effect transistor (184).

not every motherboard of the power IC494CN and field effect transistor mentioned above is fixed, and other boards may not be the same IC and field effect transistor.

note: when testing a field effect transistor or other types of power transistor, it is generally good to test that it has voltage input and output, and if it has input and no output voltage, the transistor is broken.

when measuring 1.5V and 3.3V, you don't need to plug in the CPU, but when measuring 1.8V-2.2V, most boards need to plug in the CPU to measure, for example, 184 tubes to see if there is a voltage of 1.5v.. Note: When testing SOCKET37CPU, short-circuiting 3 pins in the first row and 4 pins in the second row of CPU pins is equivalent to plugging in the CPU to prevent it from burning, and then testing whether the output pin of 184 has 1.5V voltage.

some motherboards must be plugged with a CPU, so that the pins of the CPU can be powered, and the clocks (CLK, OSC) RESET the reset.

shorting the first row of 3 pins and the second row of 4 pins to the CPU is equivalent to connecting a dummy load. Memory C1, C6, U1 and U6 are not read.

first, check whether there is poor contact in the memory slot.

check the ras (row strobe), cs (chip select) and VCC (power supply) of the memory.

check the circuit between PCI and memory, that is, judge the quality of Northbridge chip by measuring the A and D lines of PCI, memory slot and CPU seat

.

the clock is out of order, which may cause the memory not to be read.

the memory is over 31, and the line is skipped, and the AD line on the PCI slot is not displayed

. At this time, the AD line is mostly broken.

check the data line between the north bridge and the south bridge. Interrupt fault. BIOS problems: FF, 5, 7, 41, b < P > IRQ 1: 842 k/b; Irq2: cascade 8259 # 2

irq3: com2 (isab25)

irq4: com1 (isab24)

irq5: lpt2 (print card) (isab23)

irq6: FDD (isab22); Irq7: lpt1

irq8: CMOS clock; Irq9-irq11: keep

irq12: mouse (isad5); Irq13: 8387 coprocessor

irq14: HDD (isad7); Irq15: maintenance of HDD (isad6)

crash fault:

poor contact of CPU socket.

the cache is damaged, and it crashes after running for a certain time (you can't enter win 98).

BIOS data is missing.

when running a large file, it is mostly a memory error.

most of P2 board crashes are voltage faults and clock faults.

disconnection method. (disconnect the suspected chip to see if the resistance value returns to normal,)

elimination method (combined with other methods, flexible use).

exchange method. (replace the suspected chip with a good component)

waveform method (mainly check whether there are normal pulses on D, A and AD lines and control lines), and measure with an oscilloscope.

wave locking method: 586, connected with CPU block a23 → VCC.

486, with CPU block a23 → VCC.

premise of wave locking: the three conditions of CPU work are met, and A and D on ISA have a little waveform.

software diagnosis method: detection of serial and parallel ports. (see the method of using CHECK IT software)

digital card method: (the fault range can be roughly determined, but it cannot be determined, and it needs to be used in combination with other methods. )

Maintenance steps:

Observe the motherboard for obvious short circuit.

power on and touch the IC of each chip of the motherboard to see if it is seriously hot or cold.

beat the line, CPU voltage, external frequency and frequency doubling.

power on to check whether the CPU power supply is normal.

plug in the CPU to observe the digital card, and if there is no beat, first check the three working conditions of the CPU, and measure the waveform of the AD line on ISA on the premise that the three conditions are met.

there is no wave in d or a: BIOS, south bridge, north bridge and be line.

there is no wave in D and A: mainly check the working conditions around and around the South Bridge and the North Bridge.

d no wave: south bridge and BIOS.

There is no wave in A and D: the fault range can only be found by measuring the resistance to ground.

A and D have a little wave, but still show FF. The fault range can be determined by waveform method and resistance method. Main board perishable components

power supply: field effect tube, power supply driver IC

I/O chip, north-south bridge, BIOS.

the capacity of the large filter capacitor is reduced and the leakage is burnt.

resistance, capacitance, etc. Crystal oscillator, 74 series gate circuit. Battery

diode, triode, small inductance, safety, serial chip, small exclusion resistance

Simple method to judge the quality of motherboard chip:

Measure resistance.

there is clock input and no clock input (the chip is broken).

north bridge chip is damaged and bulged a little more.

3.3v short circuit to ground is mostly BGA fault, I/O chip, clock generator and power IC.

dbsy (data busy signal): disassemble the BIOS, plug in the CPU (three conditions are met), no wave is detected, and the north bridge is broken.

most of the faults of the new board are: power IC, I/O part and BIOS. The faults of the old board are mostly: south bridge (FX, VX), BIOS,

I/O.

Detection example of digital card:

7-9 crash; 8-9 Memory problem; 1, 4 Motherboards other than memory chips are not turned on;

1-11 are all related to memory; ╩ There is something wrong with the graphics card; U1-U6 do not read the memories C1 and C6;

5-7 keyboard has a problem; 4b has a display; B9 In addition to bus, there may be North Bridge, and there is something wrong with the memory.

there is something wrong with memory in ╘ b and ╘5 (north bridge part); 53-54 boot, but do not read the memory, not boot before;

╩ The display part is short-circuited; 8—25 Check Part P of North Bridge; 7 after RTC

is displayed, the screen prompts faults:

CPU frequency error: check jumper, setting, clock frequency, etc.

Memory capacity error: poor contact of memory slot, virtual soldering of north bridge or bad check of data, address and control line (resistance value and wave type) of memory slot

Hard disk control error or not reading hard disk: 1. Check RESET signal on hard disk interface or. 2. Check 244, 245 or exclusion associated with IDE. 3. The floppy drive of Nanqiao

doesn't read or gives an error: 1. Check the ground resistance of the floppy drive interface. 2. I/O chip 3 and South Bridge

keyboard have no function: check RESET, CLK, DATA, +5V and their related circuits such as keyboard socket, small inductance for power supply, safety

or I/O chip or p>COM port inside South Bridge have no function: 75232 +-12V, I/O chip, or chip power supply

. And south bridge

COM port and parallel port can also use CHECK IT software to check the fault location

the mouse of PS-2 is useless: I/O of power supply pin and maintenance of sound card of south bridge

1. No, 2. Can detect: check power supply, 3. Main chip, 4. Crystal oscillator.

5. CD has sound, 6. VCD is silent → mostly the main chip on the sound card is broken.

7. The CD is silent, 8. But it can detect that the power amplifier IC is broken.

9. The noise of CD is large → mostly the capacitance around the power amplifier IC is damaged. Power supply BGA→3.3V power supply.

power amplifier IC→ mostly ill-conceived 225,1819 IC.

sound card → supply 5V power.

1. No.11. Sound card driver can be installed; 12. Sound card can be installed; 14. Sound card can be detected; 15. Polished IC(BGA, main chip) is mostly used on the sound card; 16. At this time, the original disk should be used to drive this sound card.

graphics card maintenance

not displayed (no response at all, on the screen): check the power supply of the main IC, whether it is bad for the IC itself, or whether the BIOS is wrong or bad.

② Bad

Pluggable display screen ① Bad

White light

Output end Crystal oscillator input end

Obtaining AGP slot from each pin of PCI slot or AGP slot without OSC (real-time clock signal) 1. Graphics card without graphics card: Check power supply, BIOS, crystal oscillator.

2. Flower screen: the video memory ② is bad or the BIOS is wrong, the video memory at the acceleration terminal is bad, the main chip is bad, and the crystal oscillator is bad.

3. White light: obvious memory ① is bad.

discoloration: the main chip or ① ② video memory or active video memory is bad → you can unplug the active video memory first to check.

color cast: third, the color is wrong → the main chip is broken.

lack of color: the resistance or safety (inductance) at the output end of the main chip is broken.

note: inductors l and resistors r are used to replace the fuses on the motherboard, sound card and video card.

maintenance essentials BIOS function: BIOS is used to initialize the system and detect the type and quantity of equipment installed in the system.

the generation process of reset: pg → (gate circuit, south bridge )→ reset reset (B2 pin of ISA slot)