820-0840 short ppbus_g3h

[Kyle93]

Arrived with no power. No liquid damage. Found PPBUS_G3H shorted at 0.8 ohms.

Lifted pin one on L7410/20/30 but short remains on PPBUS_G3H. 3.2ohms on L7420. Mosfets should be good then.

Injected 1v but nothing is getting hot. Is it safe to inject more then 1v to PPBUS_G3H if L7420/30/40 remain off pad 1?

 

[2informaticos]

Check exact ohm resistance between PPBUS_G3H and mentioned coils.

 

[Kyle93]

2.8 ohms on all three coils

 

[2informaticos]

Is that resistance to ground, or to PPBUS_G3H???
If you lifted the coils, only one of them should get short to PPBUS_G3H.

 

[Kyle93]

resistance to ground on all 3 coils is 12.60 ohms black probe on PPBUS_G3H red probe on pin 1 coils. They are all removed during measurements

 

[2informaticos]

I asked you about resistance between PPBUS_G3H and coils; input pad of each coil, in fact.
And you still mention resistance to ground; I don't understand you.

If you have 12 ohm between and 1 ohm at PPBUS_G3H to ground, then no problem with CPU power supplies; that's good.
Should then be safe to inject voltage into PPBUS_G3H.
Start with 1V, maybe no more than 2-3V needed to find the culprit; one cap probably.

 

[Kyle93]

Q7960 was shorted.

PPBUS back to 13V but board still not booting only drawing 0.02amp. Dead CPU from shorted Q7960?

 

[Kyle93]

Could u7800 be defective? 0v on pins 12 and 21 of U7650. Reflowed U7800 with no change.

SMC_PM_G2_EN voltage fluctuates from 1v to 3.3V every few seconds

 

[2informaticos]

So you had short to ground on L7960.
I said to check all coils first, before inject voltage.

Very likely dead CPU, because of overvoltage came through Q7960.