820-01598 2019 MacBook Pro A2159 with missing 5V rail

[sekidata]

This board has had prior work done on it; I expect it was liquid-damaged. Several power rails were shorted, which I fixed: replacement of U8510 removed a short on PP3V3_G3H_RTC, and replacing U7800 removed a short on PP3V3_G3H.

PPBUS is 12.3V but briefly dips to 9V every second or so. No shorts on the big coils.

PP3V3_G3H is 3.3V but I'm missing PP5V_G3S. The enable signal for PP5V_G3S is fluctuating between 2.5 and 1.6V. What's required for the PMU to send the enable signal PMU_PVDDMAIN_EN?

 

[2informaticos]

Liquid damaged board, previously worked on other place, is probably waste of time.

"enable signal for PP5V_G3S is fluctuating between 2.5 and 1.6V"
Then 5V_G3S should also pulse.

Be sure no short (or low resistance) on any secondary power rail.
What about U7800 LDOs?
Can you enter DFU mode?

 

[sekidata]

I just saw that PMU_PVDDMAIN_EN is 150Ω to ground. A good board shows 45kΩ. I think the U7800 (PMU) I replaced from a donor board was bad and internally shorted on this pin. Will need to try another PMU.