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

sekidata

sekidata

Member
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

2informaticos

Administrator
Staff member
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

sekidata

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

sekidata

Member
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?
 
sekidata

sekidata

Member
Good call. I got an IR camera and found U7100 warmer in one corner by a few degrees °C. Removed it and the low resistance on PP3V8_AON is gone.
 
sekidata

sekidata

Member
After replacing the SPMU (U7100) the machine gets 20V and chimes. However, it is stuck in a boot loop and never fully starts up.

DFU Revive fails with error 21 and sometimes 9. DFU Restore fails with unknown error 4042. Am I correct assuming that the NANDs are likely bad and need to be replaced?
 
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