820-01700-A MacBook Pro 16” A2141 with shorted SSD

[sekidata]

This 820-01700 board arrived stuck at 5V USB-C. I found a short on the SSD0 NAND chips: it shows 3Ω to ground on L9530 (P1V8_SSD0) and 2Ω on L9580/1 (P2V5_SSD0). When I temporarily remove L9530 and L9580/1, I get 20V on USB-C (0.03A) and PPBUS is 12.6V. But no chime or startup.

Before I transplant the 4 NANDs from a donor board, I’d like to make sure that the rest of the board is functional. With the SSD power rails deactivated, I would expect this machine to chime, then flash the question mark folder. Am I wrong?

 

[2informaticos]

NO.
iBridge partition is on SSD...

 

[sekidata]

Ah, yes. This is also why DFU Revive/Restore fails without a functioning SSD, correct?

 

[2informaticos]

Of course...

 

[sekidata]

Replacing all 5 NANDs removed the shorts on P1V8_SSD0 and P2V5_NAND_SSD0 and I now measure all correct voltages. But the machine is stuck at 20V 0.04A with no startup.

No shorts on the big coils. DFU Restore fails with error 9.

PPBUS is cycling back and forth between 12.6V and 12.3V. With connected battery, the USB meter reads 20V during PPBUS 12.6 and drops to 5V during PPBUS 12.3V.

All PMIC outputs are there, except PPVCCPRIMCORE_PRIM_REG (not sure if that’s required). Also, PP1V2_S3 = 0V.

 

[2informaticos]

Where did you get the replacement NANDs?

 

[sekidata]

From a donor board.

 

[2informaticos]

Same model maintaining exact postion on the board?

 

[sekidata]

Yes, of course.

 

[2informaticos]

Cycling 10-20s, or how?

You may have a bad NAND, or solders.

 

[sekidata]

Yes, cycling PPBUS 12.6V for 15-20s, then 12.3 for 2s.
Checked NAND seating and solders and all are ok. Of course, there's no guarantee that the NANDs were fully functional on the donor board...

 

[2informaticos]

Not only shorted NAND is dead.
Sometime a NAND chip gets bad without bad reading on its power rail.
This kind of restart points to SSD...