Missing PP16V5_MESA voltage on iPhone6s
In my quest to repair my daughter's iPhone 6s, I now find that the PP16V5_MESA voltage is missing from the J4100 connector. Unfortunately I know this voltage was fine before (the screen worked), and I apparently affected something while finding and repairing a shorted capacitor in the PP2V75_MAMBA_LDO circuit.
I found the shorted cap (C4121), but only after removing U4100 and surrounding components FL3202, C4128, FL4107, C4106, FL4105, FL4120, C4124, and Q3140. I was not trying to remove them all, but one moment of shaky hands while the hot-air was flowing and the next thing I know there are parts flowing everywhere. Grr! And C4121 was so easy, way out there on the edge of the board... If only I had known that was the failed cap before... double grrr.
I ordered replacements for everything and managed to reflow all the parts listed above. It looked like it all went well, however I think U4100 did not solder correctly because I'm still missing PP2V75_MAMBA_LDO output (the input to the LDO is a good 3.8v PP_VCC_MAIN).
But the bigger problem is PP16V5_MESA is now missing. The only component in the PP16V5_MESA circuit that is near the U4100 LDO is FL4107, which is one of the parts I accidentally removed and put back. I checked both sides of FL4107 and it is 0V, so it looks like something upstream towards the PP16V5_MESA LDO.
Anyone have any suggestions? Is there a common-mode failure for PP16V5_MESA?
Is this a good question?