1. Observation method:

Observe the main chip, PCB board, power IC, and each slot.
① Observe whether the main chip has obvious burning, scorching, or burning.
② Check whether there is a short circuit in each slot.

2. Touch method:

(Power on for a period of time): Touch each chip, IC, etc. of the motherboard to see if it is overheated or overcooled.
Overheating: ①Internal short circuit, ②High power supply voltage.
Too cold: ①open circuit, ②no power supply, ③working conditions are not met.

3. Resistance method:

ISA: The first 8 D lines have the same R to ground.
In the early stage, the 20 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 8 D lines have the same R to ground.
They are generally no more than 15Ω between each other, and the difference between IRQ, DRQ and DACK is no more than 25Ω.
PCI:
Thirty-two AD lines have the same R to ground, and it is normal for some motherboards to have one that is tens of Ω smaller than the other 31 to ground.
AGP:
32 AD, 32 AD lines are the same to the ground R

4. Waveform method:

Important test points: RESET, SCLK, OSC, BE0-BE7 (signal that allows data address work) A3 (reflection of the flag of South Bridge work), CS, OE.

5. Locking wave method:

For motherboards below 586, PⅡ and PⅢ are not allowed, otherwise the CPU will be burned).
Connect the A23-VCC on the CPU socket and compare the waveforms of the test points. If the waveforms of the data signals in the same segment are consistent, if there are inconsistencies, use the resistance method to find the fault point. (Prerequisite: The three major conditions of CPU work are met, and there are some waves on the ISA and PCI slots).

6. Digital card method:

(reflect the process of BIOS self-test)
FF, 00 CPU does not work or the working conditions are not met, the motherboard has a serious fault (mainly check the three major conditions of CPU work, BIOS, and main chip).
CI, C6  memory slot (memory bar) memory control part (mainly check memory power supply, north bridge, memory slot, clock failure, etc.).
31 should be displayed. If it is not displayed, check the AD line on the PCI, there may be an open circuit or a short circuit.
C1→05→C1→05 (cycle)
1. Memory slot. 2. CPU power supply. 3. I/O chip. 4. KBC.
U1→05→U1→05 (cycle)

7. Logical reasoning method:

Mainly used to infer TTL, 74 series, the quality of the gate circuit.
NOT gate: inverter OR gate: adder AND gate: multiplier

8. Substitution method:

When the specific component cannot be determined, replace the suspected component with a good one. This method is widely used in practice.