820-4924 Voltage comes up once

[bjf]

This board was working fine for a long time and then just stopped turning on. No spill.

No short on CPU or anywhere else I've looked. No cycling. Just comes up once.

3V3_SUS stays at 3.3V.
PPVRTC_G3H stays stable at 3.3V.
5V_S5 stays at 5V
5V_S4 is at 5V and goes to 0V
PM_SLP_SUS_L stays at 3.3V
S5_PWRGD is at 3.3V
ALL_SYS_PWRGD comes up to 3.3V and then goes to 0V.

Not sure what failed here.

 

[2informaticos]

"ALL_SYS_PWRGD comes up to 3.3V and then goes to 0V"
Check which big coils get voltage at same time.

VCORE comes up too?
Check reaction at pins 7 & 3 of U1950.
Also try to start in SMC bypass mode.

 

[bjf]

Pins 3 and 7 both come up to 3.3V and 3.4V respectively. Vcore come up to 1.85V. All the big coils I can think to test are coming up normally once. No change with SMC bypass. Fan just comes up for a second too. One time only.

It's odd. This wasn't a liquid-damaged board. It just stopped working.

 

[2informaticos]

"Also try to start in SMC bypass mode."
???

 

[bjf]

I added that but it might have been after you read it. SMC bypass doesn't change anything. The only difference is that the fan spins up for a split second.

 

[2informaticos]

Try new BIOS...

 

[bjf]

Ok, I swapped out the BIOS chip and it's staying on now. I'll reprogram that chip with the original ME and serial and see where we're at. Looks like you got this on the right path though.