820-00875 dead short on PPBUS_G3H_CPU

[nik1981]

Hi I have an 00875 board with an exploded C7222. Removed the capacitor and others around it on PPBUS_G3H_CPU.

PPBUS_G3H_CPU is still shorting to ground with them removed but I can't locate the short anywhere. Its 0.000v on diode mode.

I've tried a little voltage an some alcohol to see if anything is getting warm but no luck with that.

Any ideas?

 

[2informaticos]

Which is the exact ohm value?
Always switch to ohm scale, for low readings.
Compare with good board.

 

[nik1981]

0.002ohms PPBUS_G3H_CPU to GND

 

[2informaticos]

Oooops, is about PPBUS_G3H.
I was thinking about VCORE.
Now search for the same value on all big coils.

 

[nik1981]

The closest to 0.002ohms are L7410 @ 4.8ohms, L7420 @ 4.9ohms and L7430 @ 4.9ohms. L7210-7210 are both at 10ohms. The rest are 60ohms on a couple and Kohms or Mohms to GND

 

[nik1981]

Had to edit the last post as my readings were wrong

 

[nik1981]

Do you think maybe remove U7410,20,30 to see if shorted?

 

[2informaticos]

No, as these values are higher than PPBUS_G3H reading.
In your case, is safe to inject voltage on PPBUS_G3H; should be a shorted cap.
Start with 1V, you should find the culprit with less than 2V, because of pure short.
You need powerfull (20A) lab PSU.

I hope you checked all big coils correctly!!!

 

[nik1981]

It's pulling 2.42a @2v but nothing seems to be heating up

 

[nik1981]

Unfortunately its a short within the layers under pad 1of C7220
Not sure if this will be fixable

 

[nik1981]

Took off the pad, dug down and separated the short. It had burnt the fiberglass layers under it so bad that it was shorting under the pad. I've removed the short now and i'll attempt to run trace wires in its place instead