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These coils are for MPMU and SPMU boost converters.

Check L7700 voltages too. You can also try replacing it.

Is important voltage on boost side of L8430; which shoudn't be 3.8V...

Check voltage and diode mode to ground on all buck outputs of U8100 and U7700. Just in case, replace L8430.

So main power supply is discarded; resolder F5200 now. Any fluctuation/spike on CHGR_A/BMON lines?

Post voltage for all big coils.

Very likely board has been affected by corrosion in time, probably under some BGA chips. Remove F5200 and check if C5252 voltage is stable.

Not big differences. MPMU LDOs are in page 43 (LDO OUTPUTS). PP1V5_MPMU_VREFADC isn't there. Also, if PPVDD_LDO20_14_8_3 isn't present, you can't expect any LDO derived from it. Only LDOs directly derived from 3V8_AON must appear in first moment. PP0V88_S1 should appear later; so...

"A1990 820-0928" Can you tell us what exact board do you have there?

Check diode mode to ground on the lines with missing voltage. Compare with working board. If not the same model available, compare with a similar platform.

"Check RD560 and its traces" Broken trace.... If you bypassed RD560, M1 CPU can't supervise 3V3_S2 current consumption.

Check RD560 and its traces.

There are more LDOs for MPMU and you didn't post any SPMU LDO yet. BTW, don't bother with "NC" marked ones.

As I said, SoC ROM is reflashed when DFU completes. You have another problem, that breaks DFU process. What was the initial symptom/problem of the machine? Anyway, here you have a dump to play with. https://drive.google.com/file/d/1DiarRnMLJlozA94KlSUQN2EEj8uVyj80/view?usp=sharing

Any history available? "Keyboard and Trackpad are functioning" Do you mean that Caps Lock LED reacts correctly? Did you check USB activity and external video?

First of all, welcome to the forum! Which area has been affected by liquid? Remove F5200/1 and see if power meter still restarts.

"Check J4401/2 voltages and signals" Do that with touchbar connected.

Check voltages and diode mode around U7800 (adjacent small coils); compare with good board. Do the same for diode mode on big coils, including SSD power rails.

Fix 3V3_S2 problem; check UC710.

Do you get correct LDO voltages on both chips? 3V3_G3H_RTC is good?