Chosen Solution

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?

MESA doesn’t have anything to do with the screen, it’s for the TouchID sensor in the Home button. If you want to properly test FL4107, you should test it in resistance/continuity mode to see if it good. A ferrite bead should measure essentially 0 Ohm across it’s two terminals. Any kind of resistance would point to it being damaged. You’ll also want to measure PP16V5_MESA relative to ground to see if that output line is shorted. Could be a bad capacitor on the line, or something got moved (and possibly bridged) when everything else got blown away. I would also inspect the components in the MESA circuit (U4040) to insure all the passives are ok. MESA is essentially a Boost Converter so the switching coil has to be in good shape as does the PMID capacitor. Let me know what you find.