820-01041 Unable to complete Touch ID enrollment

I have a 820-01041 that was liquid damaged and did not turn on. I fixed all of the damaged areas on the board and it now turns on and boots fine, but I am not able to setup touchID for some reason. Its not the normal error you get if the power button is not the original one, and there was some heavy liquid damage around the U4900/10/20 area (see photo from before I cleaned and replaced parts). I replaced all 3 of those and a bunch of the other components around that area, but I still get the same error. When trying to add a fingerprint, it will get to the point where it asks me to place my finger on the touchID button, and then as soon as I do, it gives me the error "Unable to complete Touch ID enrollment". Checking voltages with just the board on the desk with charger and another power button connected, I have PP1V8_MESA and PP3V3_MESA, but PP16V0_MESA is missing. It looks like U4900 creates that rail, but MESA_BOOST_EN is also missing. R4923 and R4954 are good. I'm confused on how this circuit works, so hoping someone can help figure out why I'm missing PP16V0_MESA and MESA_BOOST_EN
u4900.jpg
 

2informaticos

Administrator
Staff member
Check R4954 and its traces.
16V enable comes from Touch ID, through J4900 and R4954.
Can be bad Touch ID, corroded connector, or internal traces between both sides of the board.
 
I checked all the traces and resistors in the area and they are fine. I have another one of these boards that is fully functional, and that one also does not have any voltage on MESA_BOOST_EN, but touchID still works. I guess that voltage is not required for touchID functionality. I will assume the issue is with the touchID button itself and not waste anymore time on this. Thanks anyway.
 
Update on this one. I still have this board so decided to take another look at this. Found that MESA_INT_CONN was shorted to ground, only when the power button was connected, so the short was coming from the touchID button itself. The pad on the power button flex cable for that signal was burnt a little and shorted to the one next to it so I had cut it out and run wires to reconnect all the connections. It doesn't look pretty, but it works correctly now and I can configure touchID. Hopefully this helps someone else.
WIN_20210330_23_34_11_Pro.jpg
 
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