Chosen Solution
so i have a 5s that came to be because it wasnt charging. after opening it i found it to have water damage. did some probing and came to the conclusion tristar needed to be replaced. after that its pulling arounds .5 amps through the charger and battery voltage is rising..however now i cant get the phone to boot past apple logo even with power from dc psu. i compared pp_batt and vcc_main to a known good board everything looks good there. then i moved to fpc connector and in diode mode i checked the voltage drop on every pin seems good. then i connected a screen and while it was powering up i tested to make sure the 5.7v was present as well as the 1.8v data line. both are there and functional. also when i try to boot it with dc power it draws 130ma, apple logo shows a 3ish seconds and then goes black. but it continues to draw the 130ma even when the screen goes dark. already tried to dfu restore and i know my tristar replacement is good, i do them all the time and can confirm the phone is now charging. what can i check now? any ideas would be appreciated. main place i found corrosion was at the top of board between front camera fpc and digitizer fpc. also at the bottom of the board near the battery connector and charge port. also it was ultrasonic cleaned a few times with a crest ultrasonic cleaner and branson ec
Just to confirm, because you don’t mention it specifically, did you remove the shields before putting it in the bath? You said you tested the fpc in diode mode…which one ? It sounds like it was kinda working before you got it, minus the charging issue but now it is boot looping. I would take a step back and start probing the outputs of the PMIC to see if anything is shorted. Then power up the board again and test the output voltages of the PMIC. If something is amiss, it could help you identify the problem. Boot looping means a subsystem is failing during the boot process. The PMIC powers all of the critical digital subsystems. You could also check PMU_RF, which does the same for the RF subsystems. Probe and report back.
