820-00840 No Power - PPBUS_G3H Was short to ground

[ZAKLINTOWN]

Hi guys,
Have a feeling that this is a hopeless case but before I dump the board want to see if anybody might give me a hand with this,
So basically board came in with no power, got 20V on charger 0.02A - 0.11A, checked rails and PPBUS_G3H was 0.04 short to ground,
Injected 1V board was pulling around 2.5A but nothing really got hot, after a while suspected U7210 getting worm, didn't inject more than 1.4V, replaced it and short was gone,

PPBUS_G3H 13V stable
PP5V_S5 5.01 stable
PP5V_S4 as soon as probes touching it's 0.00 then quickly jumps up to 3.5V, 4.7V and back to 0.00 and so on... (NO SHORT)
PP5V_S0 as soon as probes touching it's 0.00 then quickly jumps up to 3.5V, 4.6V and back to 0.00 and so on... (NO SHORT)
PP3V3_S5 3.34V stable
PP3V3_S4 as soon as probes touching it's 0.00 then quickly jumps up to 1.5V, 3.3V and back to 0.00 and so on... (NO SHORT)
PP3V3_S0 as soon as probes touching it's 0.00 then quickly jumps up to 1.2V, 3.4V and back to 0.00 and so on... (NO SHORT)

Checked rest of the rails and can't find any short

Just poked probes around big coils and have stable 1V on L8060 as well...

 

[2informaticos]

Dead CPU, overvoltage because of shorted U7210.
Why you people still inject voltage BEFORE discarding high-side shorted MOSFET???
Is something I will NEVER understand.
Such a simple thing, which must be cheked before applying any power to MLB.

 

[ZAKLINTOWN]

Thanks for confirming this
Just wondering here - was it dead cause of the shorted mosfet or cause injected 1V ?

 

[2informaticos]

1V couldn't kill it; if you really didn't inject more.
I hope you will STOP to do this in the future...

 

[ZAKLINTOWN]

Well see it was my own board I was experimenting with but still sad if I killed the cpu,
If i didn?t kill the cpu by injecting more than 1V on PPBUS_G3H so did that happen while mosfet originally got blown? So technically there was no fix anyhow right? Or what steps would you take in that case? Sorry if I?m bothering you there, no rush anyway, it just good to take an example from somebody who knows more...
I appreciate any help
thanks very much

 

[2informaticos]

When high-side MOSFET connected to PPBUS_G3H gets shorted, you can expect fatal damage.
Less than 5% chance the CPU survive.
Seems that you are in the non-lucky 95%...

 

[JohnB8812]

CPU is dead when U7210 shorted RIP.

 

[ZAKLINTOWN]

Ok great to know, thanks a lot for this!