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Update: I ended up replacing all 4 NAND chips plus the PMIC chip U9000. Functionality has been restored.

If I replace NAND chips from a donor board, can I do a single chip replacement? Pairs? Or all 4?

L9080 is showing 0.42, definitely no short on PP2V5_NAND_SSD0. But I noticed that one of the NAND chips (U8900) is getting hot along with U9000. Possibly a shorted NAND drawing too much current from U9000?

When I remove F7000, PPVBAT_G3H_CHGR is steady at 12.3V. PPDCIN_G3H is steady at 5.1V.

I'm assuming you mean F7000, the PPVBAT_G3H_CHGR fuse?

No obvious liquid damage on this board. PPDCIN_G3H cycles between 5V and 0V several times a second. PPBUS cycles between 0V and 12.3V. When I connect a battery, USB-C is around 20V and PPBUS is around 11V. No shorts on major coils, but I found the Ocarina PMIC chip U9000 getting hot. Could a...

PM_RSMRST_L is 0V and never goes high.

PM_SLP_S4_L is 0V and does not change when I connect SMC_ONOFF_L to ground.

PM_PWRBTN_L drops to 0V when I trigger SMC_ONOFF_L.

I have a 820-00281 board that came in with liquid damage and completely unresponsive. After removing a capacitor that had shorted PPBUS_HS_CPU to ground and replacing all four CD3215, I now get 20V on USB-C but 0A. PPBUS_G3H: 12.6V PP3V3_G3H: 3.3V PP3V3_PMICLDO = 3.3V PP1V25_PMICVREF = 1.24V...

It's still 0V.

So no other ideas on this one?

Here are the Buck converter output test points for the PMUs.

I replaced U8100 from an identical Air 2020 donor board. However, the situation is unchanged, with rapid voltage fluctuations on all PMU outputs. MPMU_VREF_ADC is still 0V.

Donor board is the only source available, correct?

1.5V

MPMU_VREF_ADC shows 0.58 (300k on Ohmmeter), which is exactly the same as on a good board. Perhaps the MPMU U8100 is bad?

If there is an overcurrent situation, how would you find the culprit?

Thanks, you're right, I got confused by the "LDO" in the rail name. However, note that the schematic does say that PP1V5_VLDOINT_SPMU is an output. Here are my complete output voltages for U7700 and U8100: SPMU: PP0V72_S2_VDD_LOW: fluctuating 0-0.7V PP1V2_AWAKE_PLL: fluctuating 0-1.2V...

I'm trying to understand the fluctuating power rail issue. The wildly fluctuating voltages are all buck converter outputs of the PMUs U7700 and U8100. The PMU power input is steady at 3.8V. The LDOs (PP1V5_VLDOINT_MPMU, CAP_PPSPMU_VLDO9, PP1V5_VLDOINT_SPMU) are steady. What tells the PMUs to...