tcampbell34
Member
Hello. I have a 820-00928 board that had liquid damage around U4200, U3900 area and PPBUS was shorted to ground inside the board under Q3501. I was able to dig the short out and replaced Q3501. I cleaned and replaced a bunch of corroded resistors around U4200 also and the board turned on and booted to the OS fine. The touchbar was on, but it was not responding to touch. I reinstalled a fresh copy of big sur on it but it was still not responding to touch. I did confirm that touch ID was working after reinstalling big sur on it. I found that pin 15 on J4402 was OL, so it was not connected to U3900. I removed U3900 and confirmed the trace was broken. I ran a small wire under U3900 to reconnect this trace and also had to replace U3900 with one from a donor, because I found the original U3900 was damaged. I replaced it with one from the same model donor and now it boots and touchbar responds to touch like it should, but now touchID does not work. When I try and add a fingerprint, it gets to the point where it asks me to place my finger on the scanner, but then it immediately says it failed. I know the touch ID button is paired with the board but is it paired specifically with U3900? I already tried replacing U3900 again with another one to rule out bad soldering, but I have the same issue still.
