Laptop Model: Lenovo G580
Version Number: LA-7981P
Fault :Laptop Power On & Off Problem
Maintenance Process:
The bare board is powered on for 0.8 seconds, powered off for 0.2
seconds and restarted. As everyone knows, this fault is caused by the
disconnection of pin 10 VRMP power supply CPU_B+ of the CPU power supply chip
NCP6132.
After measuring that CPU_B+ is not disconnected, we soldered PR929
and tested 0.8 after power-on without powering down and restarting. I was
secretly happy. I thought the repair was over, but misfortunes never come
singly.
The code did not run after installing the memory and powering it
on.
After repeated testing, the
current sometimes stops at around 0.5. Because I have repaired several boards
before, the current is probably still very clear. After lazy flashing two
BIOSes, there was no result, so I went straight to PLT_RST#.
The actual measurement on the network card interface is low level, and
it can be inferred according to the timing diagram.
The bridge needs to get the SYS_PWROK (VR READY) PCH to generate
PLT_RST. Follow the source of SYS_PWROK and send it out from the gate circuit
of U15.
The measured
VGATE of pin 1 is low level, PCH_PWROK of pin 2 is high, pin 5+3VS is normal,
and SYS_PWROK of pin 4 is low. It is obvious that the fault is here.
VGATE is sent
by the CPU power supply chip NCP6132. Changing the chip has no effect. I
removed U15, connected pins 2 and 4, and successfully ran the code and turned
on the computer.
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