MacBook Air 820-01521 with DFU issue

[sekidata]

This 2018 Air board is at 20V USB-C, with PPBUS at 12.6V. I have AWAKE, SLPS2R, and NAND rails. No shorts I have found yet. The machine had a liquid-damaged trackpad, which I replaced. No signs of life, not even trackpad clicking.

DFU Restore brings up the Apple logo and progress bar on the target computer but it fails with "AMRestoreError Domain -1 - Failed to handle message type StatusMsg (Generic Error)".

Anything else to check?

 

[2informaticos]

Possibly bad SSD, or short on some power rail.
Check diode mode to ground on all big coils and SSD rails.

Did you try DFU with battery connected too?
Is the battery charging?

 

[sekidata]

Every single large coils has the same resistances as on a good board. PP2V7_NAND is fine and produces 2.5V.

I connected a known-good battery during DFU Restore and it made no difference. The machine always ends up in Recovery Mode after the failed Restore.

Yes, the battery was charging (getting warm and USB-C drawing 1+ A).

 

[2informaticos]

Reflash SoC ROM and try again DFU.

 

[sekidata]

I'm not set up for flashing chips. Would transplanting the SoC ROM (U4770) from a donor board work?

 

[2informaticos]

You can try...

 

[sekidata]

I tried the ROM chips from two donor boards but neither worked. Same error during DFU Restore.

 

[2informaticos]

Read this page and check if missed something.

DFU Mode Restore (Macs) - LogiWiki

We have Apple MacBook and iPhone Diode readings and general fault finding information compiled by the leaders in this area

logi.wiki

 

[sekidata]

I noticed that the PMU (U7800) gets hotter than on a normal board. Any advice for troubleshooting it other than checking each small coil?

 

[2informaticos]

U7800 should be good, if you get Apple logo and progress bar.