Lenovo e425 notebook no power on repair

maintenance is over.

Machine model: Lenovo e425
Board No: llw-1 amd MB 10330-2
Fault phenomenon: notebook no power on, standby current 0.02
Maintenance analysis:
The customer sent the Lenovo e425 machine to Taiwan, saying it was no power on, and the standby current was 0.02.

Lenovo e425 notebook no power on repair Figure 1.

Lenovo e425 notebook no power on repair Figure2.

After dismantling the machine, it was found that water damage corrode was found in BIOS. After cleaning, it was still the same as no power on.

Lenovo e425 notebook no power on repair Figure 3.

Lenovo e425 notebook no power on repair Figure 4.

Measure the 472 resistance under BIOS. Because the 1pin of corrode is broken, 3.3V of VCC on the repair part is connected to BIOS pin, but the fault is still no power on.Scan the BIOS data and replace the BIOS body. The fault is based on no power on. When measuring the standby chip (bd95280muv), there is no 35V output, but there is a linear 35V output. After measuring the standby en pin, it is found that there is no high potential. After checking 3V_5v_There is no VCC in en.

Lenovo e425 notebook no power on repair Figure 5.

It was renamed S5 by a resistor_Enable (this signal was sent out after pressing Switch switch) from the EC chip. Is the EC broken?There is a post on the forum that the standby chip is easy to be broken. It is common failing. Since there is no standby chip to replace, it can only be put aside to find other places.After checking the drawings, it is found that S5_Enable is pulled up to 3d3v by removing resistance_TO_KBC (measured at 3.3V),Give it to S5_Enable Jump wire to 3d3v_TO_On the KBC, the standby 3v5v VCC is found after power on, indicating that the standby chip is good (the BIOS chip was removed before, and there was no standby 3v5v VCC output, so it is ruled out that there is no 3v5v standby due to incorrect BIOS data).Why does EC not issue S5_Enable, is EC broken?When there is no way to do it, use a magnifying glass to carefully observe water damage. It is found that r6010 is not directly connected to each other.multimeter measurement is actually disconnected. Supplement add solder line short-circuit, and then power on Switch, the current of switch can be trotted to 1.3 by pressing Switch, and the screen shows. This is the end of maintenance.