820-00850 board with 20V but no signs of life

[sekidata]

This 2018 A1989 board shows 20V on USB-C pulling 0.05A. No liquid damage. I have PPBUS_G3H at 12.6V and the SLP and AWAKE voltages are present. It is missing all G3S rails and their G3S_EN signals, which come from the PMU U7800.

What does U7800 require to produce the G3S_EN signals?

 

[2informaticos]

Try DFU revive first; restore, if no important data to save.

 

[sekidata]

The machine enters DFU mode but since all SSD power rails are 0V, the DFU Restore fails with the timeout error. I need to get my power rails restored first.

 

[2informaticos]

Check diode mode to ground on SSD power rails.
Many times, SSD and G3S voltages appear after complete DFU.

 

[sekidata]

The SSD power rails are all free of shorts. I'll try DFU Restore again with/with battery and with/without charger.

 

[sekidata]

No luck. I've tried 6 times to Restore/Revive and I always get the "gave up waiting" error. SSD and G3S rails are still missing.

 

[2informaticos]

Check for short on any other big coil

 

[sekidata]

All big coils measure the same resistances to ground as on a good board.

 

[2informaticos]

The battery is charging?
Keep it connected in DFU...

 

[sekidata]

Mystery solved! I just did a gentle reflow of the PMU (U7800), just in case it was the problem point. This restored the SSD and all other power rails and the DFU Restore went through. I can't say for certain why this worked but the machine is up and running now.