820-00875 dead short on PPBUS_G3H_CPU

nik1981

Member
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

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

2informaticos

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

nik1981

Member
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
 
Last edited:

2informaticos

Administrator
Staff member
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

Member
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
 
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