820-2879 PPBUS_G3H Dropping from 12.6 to ~5V then back to 12.6

[Therealkilometers]

So I have a 820-2879 were PPBUS_G3H will sit at 12.6V for a few seconds then slowly drop to 5V sit there for a few seconds then back to 12.6 and repeats. I think i have narrowed it down to CHGR_AGATE it will be at 16V then drop down to 6V for a bit then back to 16 causing Q7085 to not output the correct voltage. This happened with or without F7040 on the board. Does anyone have any idea why this is happening and how to fix it.

 

[aprendiz]

voltage is stable at pin 2 from U7000?? check sense resistors from U7000 (R7022-R7021 and R7051-R7052), corrosion on R7085-R7086 or around U7000??? if everything is right remove F7040 and check if 12.6V stabilizes...

 

[Therealkilometers]

voltage seams stable at pin 2 of the U7000 ~16.3V. All the current sense resistors are fine. And yes it drops even with F7040 removed

 

[dukefawks]

Is PP3V3_S5 pulsing too? What is the history, liquid?

 

[Therealkilometers]

I believe PP3V3_S5 was pulsing as well. But i went to go mess with this board today and it magically lost its green light over night and now has a short to ground on SMC_BC_ACOK. This board is going to meet the bottom of the pile for a little bit.

 

[larossmann]

SMC_PM_G2_EN is going to enable PP3V3_S5, which comes from the SMC.

SMBUS_SMC_BSA_SCL/SMBUS_SMC_BSA_SDA talk to the U7000 to set the voltage of PPBUS_G3H, which come from the SMC.

SMC_BC_ACOK, which you say is shorted to ground, connects through the SMC.

See a pattern?

 

[Therealkilometers]

I do... Sadly... And this is why this board is sitting in the pile.