Lenovo ThinkPad E430 does not trigger repair

Machine model: Lenovo ThinkPad E430

Fault phenomenon: the motherboard enters Xiaoqiang, which is very dirty and does not boot (does not trigger)!

Motherboard status: there are obvious cockroaches, the tin spots are white and dirty, and there is no obvious burning and blackening place.

Power-on: Power-on does not automatically trigger (no small battery), the standby voltage is about 0.02A, and there is no obvious leakage, which is normal.

Maintenance process:

Remove two BIOS, one 4M and one 8M, back up the old BIOS, brush the new BIOS, and power on the test. The phenomenon is the same. Power-off resistance, no obvious short circuit, power-on test, 3V5V, no memory voltage, no 1.05V, no CPU voltage. Standby conditions should be normal, and there may be a voltage shortage. Looking for drawings on Xunwei, and searching for some maintenance examples of the same model, I read several articles.

According to the drawings, check all circuits. When PQ202 is checked, it is found that the voltage of pin 3 is 3V jumping, the voltage of pin 2 is 20V normal, and the normal conduction is 20 V. Start again after the power failure, and the result can be triggered, and the voltage can only rise to about 0.1-0.3A to settle. It is estimated that the fault point is here. Repair welding and tin (red circle in the third picture), then power on, short-circuit normal trigger with buzzer, voltage jump rises to 1A, and finally set at 0.8A Connect the keyboard, and the case can be turned on and off (only bare board), which proves that it has entered the BIOS.