820-00239 missing PPBUS_G3H


Hi all.
I have a dead 820-00269 from an A1706.
Missing PPBUS_G3H.
I get 20v on F3001, however no voltage on F8400.

I removed F8400, and injected 1 volts into pin 1 and found U7960 getting very hot.

I removed that and there still appears to a direct short (zero ohms) to ground on the pads of pins 6,7,8 - (PPVCCIO_PHASE, which becomes PPVCCIO_S0_CPU, after L7960)

With U7960 still removed, I now get 13.03v on pin 1 of F8400 (PPBUS_G3H).

I understand that some CPU rails will normally appear to have very low resistance, but I don't assume it should show zero resistance?

The only other components on PVCCIO_CPU are a bunch of caps - C7964, C7965, C7966, C7967 and C7970 and C7971
I removed C7964 but the short remains.

I've removed the board and applied 1v to PPVCCIO_S0_CPU.
It still shows a short -its drawing approx 2.5A at 1v.
Nothing seems to be heating up however.

A dead CPU perhaps?
Any suggestions greatly appreciated.
Last edited:


Staff member
Remove F8400 why?

Injecting voltage into PPBUS_G3H without checking first for shorted high-side MOSFETs???
Hundred times explained in the forum...

In the moment when U7960 got burnt, a spike from PPBUS_G3H went to CPU; very short time, but enough to fry it.
This kind of problem is fifty/fifty; sometime CPU can survive, depending of the peak of voltage.


I'm still learning!
I removed F8400 to see which side had a short.
I only injected 1v, which I thought would be safe. :(
The max amps it drew was 2.5A.

So do you recommend replacing U7960 and hoping?


Staff member
With 0 ohm resistance to ground (pure short), very likely dead CPU.
However, nothing to lose if try...