Dell Inspiron 5593 shutdown after 5 seconds

[DrFalken]

Hello everyone!
Motherboard model: FDI55 LA-J081P
Today a customer delivered this laptop completely dead, with the original power supply shorting when plugged into the connector.
I found and replaced a shorted MOSFET (PQZ3).
Now the laptop turns on (fan runs fine but no video signal) and after 5 seconds it turns off.
BIOS has already been updated (both 64MB and 128MB IC)

+3VALW and +5VALW are still present.
+VCCIN = 1.8V stable (measured on PLZ1 at power up)

Abnormal readings:
PLZ1 to GND = 0 Ohm
PLZ2 to GND = 0 Ohm

What else should I check?

Schematic - https://www.badcaps.net/forum/troubl...schematic-need

[mcplslg123]

PQZ3 is hig side mosfet and since it was shorted 19V has reached SOC.

Your SOC is shorted and problem can be solved only by replacing SOC. Else Game Over.

[DrFalken]

PQZ3 is hig side mosfet and since it was shorted 19V has reached SOC.

Your SOC is shorted and problem can be solved only by replacing SOC. Else Game Over.

Thank you for the reply.
I suspected the SOC was shorted because it gets really hot in the 5 seconds the board is on and also the resistance to GND on those 2 inductors is way too low.
Out of curiosity, I tried flashing the BIOS with another BIOS and the board doesn't turn on at all: if the BIOS is run by the CPU, why this behavior if it is dead/faulty ?