MacBook Pro M1 13 820-02020 stuck at 5V 0.1A

[mitchw]

Board had some light liquid damage, nothing serious, just one bad looking cap that I removed (from PPBUS_G3H to ground), near speaker amps.
There was no corrosion as such, just few tiny spots, really minor.

The board is stuck at 5V, it draws 0.1A all the time. Only at poweron the amperage surges up to about 0.15-0.18A, then it settles at 0.1A.
I put it in DFU and it didn't do anything, wasn't detected on other machine.

Voltages all seem OK near the CD3217 chips, all LDOs are present, also no liquid damage was nowhere around those.
But measuring other voltages, all of them were present when I checked the PP5V_S2 which is missing.
PPBUS_G3H is 12.3V, PP3V8_AON is 3.8V,...

So this is about what I checked, but don't know what to check next. I am not sure if the problem is with USB-C detection or it might be with CPU or something completely else

[mon2]

PP5V_S2 which is missing.

Remove all power. Meter in resistance mode. What is the exact resistance to ground of PP5V_S2?

[mitchw]

Remove all power. Meter in resistance mode. What is the exact resistance to ground of PP5V_S2?

Resistance is over 2M ohms. Diode drop is 0.315.
PP5VS2_EN is also missing

[mitchw]

Found a corroded resistor: RD531, replaced it, no change. Also that cap that was shorting PPBUS_G3H was CR604 which I removed, but it should work without it.

Next, I was checking all the LDOs and discovered that I am missing one voltage: MPMU_VREF_ADC, which is at 0V. All other voltages (except for PP5V_S2) are all present.
MPMU_VREF_ADC is not shorted and it reads 0.590 in diode mode.

So where to look next? Nothing else is looking crusty or corroded.

[mitchw]

So in essence, what I found and corrected:
- CR604 was badly corroded and removed
- RD531 was O/L also corroded and replaced
- CD3217 area wasn't affected at all, every LDO voltage measure spot on

Voltages:
-All voltages expect the following are present:
-PPBUS_G3H is 12.3V (should be 12.6V or more)
-PP5V_S2 is missing and not shorted
-PP5VS2_EN is also missing (generated by U8100)
-On the U8100 all LDO voltages are present, except for MPMU_VREF_ADC
-U7700 has all the output voltages present


So from what I have gathered, the U8100 might be at fault, but I've seen other threads of similar U8100 issues (missing MPMU_VREF_ADC), and replacing it with another U8100 didn't solve it.