820-01700 - short on U6960

[Palhano]

I found a short circuit on the PP3V3_GH3_RTC line. It was a badly burnt U6960. I removed it and the short circuit disappeared, but when I put in a new chip, I have problems with the PPBus voltage fluctuating.

As a test, I removed R6900 and the PPBus has 12.6V. If I leave the board without U6960, with R6900 in place, I have 12.6V on C6910.

I've already tested with 3 different U6960s (2 new and 1 from scrap), same problem.

I checked all nearby components and lines, everything is OK. I have the 3.3V line on L6960/61.

Any tips?

 

[2informaticos]

Remove R6934/5 and check if PPBUS_G3H is stable.
Also check diode mode to ground on pins 1 & 2 of R6934/5.

 

[Palhano]

Removing R6934/5 stabilizes PPBus at 12.6V.

R6934/5 in diode mode, both pins 1 and 2 have 0.450

 

[2informaticos]

So no low value at 3V3_G3H_RTC.
Not easy to find a culprit then.

Check diode mode to ground on all power rails from Intel side.

 

[Palhano]

I found changes in the U3200. When connected to that port, I don't get PPBus. I checked in diode mode and the 1.5V LDO line has 0.090.

I'm going to order this chip to replace it. Could it be the cause of the problem?

 

[2informaticos]

Be sure is not the filter cap; before touching the chip.
Just in case, don't forget to check in diode mode again; once the chip is removed (out of board) and board colled down.