Chosen Solution
I have an iPhone 6 that came in with water damage. There was the classic C5202_rf short on VCC_Main, which I removed and the short is gone. The phone will now power on, but is stuck boot looping (white apple, black background) and the PMIC gets warm. It only seems to heat up when I have 5V USB hooked up, if it’s just the battery I haven’t noticed any heat. Any ideas on where I should look for the short?
Before anything else, did you do a proper decontamination of the logic board (remove shields, ultrasonic bath, Branson EC, IPA rinse etc)? If you didn’t do this initially, then you should do it now. Once you’ve done that I would start by going “bare bones”. Disconnect everything from the logic board except the Battery and Dock. Connect an iTunes enabled computer and run 3uTools (www.3u.com) to see if the phone is still rebooting. If it is, then it is most likely a logic board issue (it could be the dock though). If you suspect a logic board issue, check PP_BATT_VCC, PP_VCC_MAIN (which you already did) and PP5V0_USB. I would start by checking to see if those rails are shorted to ground. If one of these rails is shorted to ground, then you will need to identify what is causing the short. It could be a bad decoupling capacitor, conductive debris or defective IC that is directly supplied by those rails. Then you move onto the PMIC and check the voltage rails it generates. The PMIC generates ~15 voltage rails. They are all important (for obvious reasons) but the ones to check first are as follows: PP_CPU & PP_GPU, PP1V8_SDRAM & PP1V2_SDRAM, PP_VAR_SOC & PP0V95_FIXED_SOC, PP3V0_Tristar & PP3V0_NAND, PP1V8_ALWAYS, PP1V0.The PMIC also generates, what I would consider secondary, yet still important voltage rails for the following sub-systems: PP3V0_MESA, PP1V8_VA_L19_L67, PP3V0_PROX_ALS, PP3V0_PROX_IRLED, * PP3V0_IMU, PP3V3_USB, PP3V3_ACC
Sounds like you found an solved a pp3v0 Tristar short. Great job–was it the little cap by the dock? After this, the next thing to rule out is software. If you had a short on Tristar and since Tristar is part of the main i2c data communication bus from CPU then software corruption is next most likely. Restore phone and see if it passes restore.
Try testing with a new battery.
