Unable to setup touch ID, board repair
Hi all! I bought a dead iphone 6 which I repaired just by replacing two vcc_main caps near backlight and working a bit on the backlight circuit itself, now it's fully working except that it doesn't let me configure a new finger. I don't get the error message upon boot that is typical when you let the home button unplugged or when you connect a different one, but rather a message when I go to set a new finger up. This leads me to believe the sensor is being recongnized but is lacking something, power or data.
Before I go into the board itself I should point out that I tried a known good long flex and also tried its original flex on a working phone.
No physical damage on any flex or the board.
Since I was working on the BL circuit which is close to the little LDO that gives Mesa the 1V8 line I replaced it but it didn't do any difference.
I did a diode mode measurement on all pins on that connector and they tested good against a working, known good board.
Now before I start replacing other chips just because, I want to understand the power sequence of the sensor.
As far as I can tell, the sensor sends the MESA_TO_BOOST_EN signal and then the boost converter should start sending the 16.5V and the other two voltage lines too, but I don't understand at which point I should be seeing them.
My first thought is when I try to set up the new fingerprint or on the lockscreen but no power or the enable lines were present at that time. What am I doing wrong? Maybe the previous owner unplugged it while energized and that killed the sensor and all this work is futile wich would suck but is pretty likely at this point