820-00164a ppbus 4v

[Yoel Ren]

so this machine came with clean board, measured that ppbus_g3h is shorted to ground, so I inject 1.5v there, replaced c7377l, short is gone, but ppbus is still 4v, but not stable, any advice ? idk where to proceed right now,

 

[Yoel Ren]

I have pp3v42_g3h, I have replaced u7000 too

 

[2informaticos]

Post U7000 basic voltages; many times mentioned.

So you've just injected voltage into PPBUS_G3H BEFORE searching for an shorted high-side MOSFET.
I can only hope you'll fry one board and then stop do this; is probably the only way to learn why.
Two many times I explained the reason, I will not repeat again here...

 

[Yoel Ren]

By high side mosfet do you mean the Qxxx thing? Or do you mean i must remove f7140 to see if the short is on system side / isl? I have remove it an the short is on ppbus..
Resistance between 17/18 and 27/28 of u7000 is 3 ohm and 21 ohm, for the details i will check tomorrow..

 

[Yoel Ren]

so I found that q7630 is shorted, I replaced it and the short is gone, fuse's resistance is more than 1 , so I replaced it too, now I have fan spin, and ppbus is 8.6v, but no chime and no image, resistance to ground on L7130 is 0.5kohm

 

[Yoel Ren]

Nvm, board turn on now.. But i still need the answer regarding is mosfet the Q7 bla bla thing? So when searching for shorted mosfet it must be done manually? ( Not by injecting) thanks before for helping 2informaticos!

 

[2informaticos]

"I found that q7630 is shorted"
Ton of luck, you didn't fry the CPU injecting into PPBUS_G3H.

"searching for shorted mosfet it must be done manually?"
If already detect the short, just compare readings from PPBUS_G3H with all big coils.
You had EXACTLY the same reading on PPBUS_G3H and L7630; guess what that meant...

 

[Yoel Ren]

yeah because before i found the short, I remove all the caps 1 by 1 and check if the short persist, well it doesnt really take a lot of time, but sometimes, the ppbus_s5_hs_computing_isns's caps doesnt resist the heat quite well and burst ( pop sound , and bad smell coming out of it ).., okay at least I learn something from this, thanks a lot for helping!