PPBUS Short 820-00840

[Mamdouh]

I have a 820-00840 board that has no power, originally customer said it was working and suddenly stopped after a restart, no liquid else than a bit on the ssd connector, put it through the ultra sonic and seems clean. pubs_g3h is shorted to ground with less than 1ohm to ground and shorted to PPVCCCPU_S0G with around 5ohms. would this be a dead cpu. Tried injecting voltage on ppbus and nothing got warm.

 

[2informaticos]

STOP to inject into PPBUS_G3H in this manner!!!

Check first if any high-side MOSFET is shorted.
If you have 1 ohm at PPBUS_G3H and 5 ohm at PPVCCCPU_S0G, then is not an high-side MOSFET from that power supply.
But you MUST compare with ALL big coils.

Only inject if you are sure no high-side MOSFET is shorted.
In such case, you can increase voltage, untill heat something...

 

[Mamdouh]

What is considered a high side mosfet? how do i check if they are shorted and what do i compare big coils with

 

[Mamdouh]

L74(10,20,30) all had less tha 1ohm to ground removed corresponding u74** and no short on ppbus anymore. Ppvccgt_s0g is shorted which i assume was responsible for the 3 coils. That line just goes to the cpu and some caps could it be a bad cpu?

 

[2informaticos]

So you had shorted high-side MOSFET.
Injecting voltage on PPBUS_G3H could very easy killed CPU.

Low values on CPU coils can be normal, just compare with similar board.
But not too many chances to have a good CPU, after what you did on PPBUS_G3H.

 

[Mamdouh]

Only injected around .7v the board didnt take anything more than that even for the first time. Coils ended up going down to 0 ohms after waiting a while. if cpu isnt dead wat should i do next

 

[2informaticos]

You should compare ohm values with similar board.
Less than 1 ohm is not good sign...

 

[Mamdouh]

I'm getting 3.5ohm on those 3 coils on another board. if i do leave the probes on this board, it goes down to 0 or 0.1 theres not much left on that line is there anything left to do?

 

[2informaticos]

Dead CPU, trash board...