820-01700 (A2141 2019) with USB-port problem

[sekidata]

I have this A2141 that came in with no power. I found a dead left USB port (heavily corroded plug receptacle). With a good USB board, the plug still did not work (USB meter turned on & off repeatedly), so I suspected damage to the CD3217. I replaced both CD3217s on that side (U3100 and U3200) from an identical donor board.

Now I get 5V on all four ports, but no 20V or any signs of life. PPBUS is 12.3V. No shorts on any big coil. The only (maybe) abnormal finding is that PP3V3_G3H_RTC_X appears to be less than 100 Ω to ground, but shows a steady 3.3V when powered. I'm using a 96W charger.

Where to look next to get 20V established?

 

[sekidata]

Correction: PP3V3_G3H_RTC_X measures 60 Ω (0.05 diode mode) right after unplugging USB power but over several minutes increases to the expected 500+ kΩ (0.40 diode mode).

 

[2informaticos]

Always allow 10-15s before checking in diode mode, or ohm scale.

Did you maintain the position for U3100/200?

Try reflashing corresponding TBT ROM; make backup first.

 

[sekidata]

Chip position is the same as on the donor board. I also transplanted U2890, the TBT ROM from the donor board.

When I connect a charged battery, all 4 ports show 20.6V but 0.00A.

 

[2informaticos]

What is the current consumption with charger alone?

 

[sekidata]

The USB meter says 0.09A.

Curious observation:
I connected a power button to the logic board and I got the machine to start up by long-pressing the power button several times. This worked once, then nothing again. I had the battery connected for this. The entire system appeared functional when the start-up worked, but as soon as I shut it down, it went back to unresponsive. What could cause this sort of inconsistent behavior?

 

[2informaticos]

Disconnect Touch ID and use a switch soldered to PMU_ONOFF_L.

 

[sekidata]

Same behavior with PMU_ONOFF: I got it to start up once again (fully functional), and then nothing on the next 20 attempts. Could this be a firmware issue?

 

[2informaticos]

What is PMU_ONOFF_L voltage (without pressing the switch)?

 

[sekidata]

I just did a DFU Revive (with connected battery) and the machine is now up and running, starts up normally, and passed all diagnostics.