820-3115-b, no chime, no brain, no video

[Rabbithole87]

Hi,
This 820-3115-b board came in not booting with no video.
Green light on the charger but no fan spin.
The Board had no signs of liquid damage, was very clean, with no corrosion.
I found out that ppbus_g3hot was shorted to ground by cpu vcore.
Q7550 was short, so I replaced Q7550, Q7520, Q7510 and U7400 as recommended in one of Louis videos.
A trace was burned between Pin 3 of Q7550 and Pin 2 of R7555, I fixed this with a jumper.
This restored CPU Vcore
PPVCORE_S0_AXG = 0,896 V
PPVCORE_S0_CPU = 0,811 V
But I still have no chime and no video.
Fan is spinning now, it starts slow but gets faster and faster upto high speed.
I've replaced SMC and BIOS with same result
Board beeps with no RAM installed.
Tried known good RAM.
No light on USB Mouse.
I inspected the area of U7400, measured every single resistor around U7400, everything is fine.



Thank you

 

[TCRScircuit]

CPU will probably be dead. RIP.

 

[dukefawks]

Could be a bad CPU, the question is how did the initial damage happen. I bet it was liquid or someone fucking with it.

 

[Rabbithole87]

My first guess was a dead CPU too. But I can really say that there was no history of liquid damage or prior repair attempt. I think the CPU just died when Q7550 went short.

 

[Rabbithole87]

Are there any signals that I can measure, which should be missing, to proof that the CPU is definitely dead?

 

[dukefawks]

Not much to test besides slapping a known good CPU on there.

 

[Rabbithole87]

Ok , thank you very much duke. Mark this as closed or solved.