Air A3114 2024 M3 (820-03286) stuck at 5V USB-C

[sekidata]

The machine has no signs of liquid damage. USB meter shows 5V 0.16A. PPBUS is 12.3V. PP3V8_AON is present. The main PMU (U8100) does not produce any power rails, it appears to be off despite good input power. What signals are required to turn it on?

 

[2informaticos]

Dont you get any LDO from MPMU?

 

[sekidata]

PP1V5_LDOINT_MPMU is 2.0V. Nothing else.

 

[2informaticos]

Possibly bad MPMU.
If it gets 3.8V on its VDD_LDOx inputs, should generate corresponding LDOs.
Check diode mode to ground on its LDO lines.

 

[sekidata]

No shorts on the LDO lines. U8100 gets 3.8V inputs but lines like PP1V2_AON_MPM or PP1V8_AON_MPM are 0V.

 

[2informaticos]

Then replace U8100...

 

[sekidata]

After removal of U8100 I noticed that PP3V8_AON is 50Ω to ground. Enough resistance to produce 3.8V but probably not enough to power either PMU. I'm assuming that without a good thermal camera, this short will be impossible to find?

 

[2informaticos]

Yeah, only performant IR camera can show you small differences.