820-01521 2019 Air not starting up

[sekidata]

This 2019 Air board is at 20V USB-C (0.02A) with PPBUS at 12.6V. No signs of liquid damage.

It enters DFU mode but any T2 firmware restore attempt ends with error 9, even with connected good battery and Apple charger.

No shorts on the big coils or the small coils around U7800. I am missing the S5 power rails as well as PP1V2_S3. Also missing are some of the power-good input signals into U7800: PVCCIO_PGOOD, CPUVR_PGOOD, and PVDDQ_PGOOD.

Anything else to check before I blame this on a faulty T2 chip?

 

[2informaticos]

Try reflashing SoC ROM (U4770)...

 

[sekidata]

Do you have any hints for how to get a reflashing setup started? What's the best way to be able to handle different sizes of chips?

 

[2informaticos]

This may help you.

820-00850-A - Tries to turn on and restarts

I do have a CH341A Linkj ->...

boards.rossmanngroup.com

Try to read all the threads in the forum, not only personal ones; at least the recent posts.
You may find interesting information...

 

[sekidata]

I reflashed the SoC ROM, but subsequent DFU Restore attempts still fail, this time with a different error (below). Now the board is in perpetual DFU mode, with PPBUS between 11.5 - 12.3V.

 

[2informaticos]

Force the machine off first.
Then try DFU keys combination again.

 

[sekidata]

When I force the machine off with the power button, it disappears in Apple Configurator for a second, then immediately reappears with the DFU icons on its own.

 

[2informaticos]

Try again with original SoC ROM dump.

 

[sekidata]

I confirmed on another machine that the persistent DFU mode is the default state after reflashing the SoC ROM. The board enters DFU mode as soon as power is applied, ready for a DFU Restore.

On this particular board, DFU Restore fails (I think) because I'm missing PP5V_G3S and PP2V7_NAND.

 

[2informaticos]

I got several times SSD voltages after DFU revive/restore.
So DFU should fix it; unless is caused by another problem, not T2 corruption.

 

[sekidata]

When I revert to this board's original SoC ROM dump, I still get the above error ("added from invalid state Restoring") during Restore attempts.

 

[2informaticos]

You may have SSD problem, or T2 itself.
Check for short on all secondary power supplies, from S4 to S0.