820-01987 2020 Pro board with cycling USB-C voltage

[sekidata]

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 malfunctioning U9000 cause PPDCIN_G3H to cycle?

 

[2informaticos]

Remove F5200 and check C5250 voltage (without battery).

 

[sekidata]

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

 

[sekidata]

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

 

[2informaticos]

Sorry, I got confused, thinking you have 02020 board.
Looks like your board gets into protection, when secondary power supplies try to start.
U9000 can cause such problem.

Did you check diode mode to ground at L9080?

 

[sekidata]

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?

 

[2informaticos]

That seems to be the case...

 

[sekidata]

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

 

[2informaticos]

You can try replacing one by one.

 

[sekidata]

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