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iPhone 7 Pmic seems to be failing?

I have checked in an iPhone 7 that seems to have spontaneously gotten extremely hot and then gone dead. As soon as I plug it into my dcps and turn the power supply on it pulls max amperage immediately without being prompted to boot. I immediately checked vdd main and vdd boost for shorts and the diode mode readings seem to be good, checking from a couple different points on the board. Next I checked for heat with freeze spray, and the pmic seems to get extremely hot immediately upon turning on my dcps. I checked the lines in the area of pmic where it got hot, which seemed to have been vdd main, vdd boost, nand 0v9 and nand 3v0 as well as a couple others, but I have no detectable shorts on any of them. Is it possible that the pmic itself is bad? Anything else I should check before attempting pmic replacement?

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The PMIC doesn’t fail very often and it’s not exactly an easy removal either. The last thing you want to change (other than a CPU/SDRAM reball) is the PMIC so check all the outputs, especially all of the ones that have coils on the output as they are the high current rails. Check in diode mode first and then in voltage mode if you can’t find any shorts.

This is when a thermal camera can come in handy because you can see where the heat is distributed. I had a similar case and I could see the CPU/SDRAM “heartbeating” a thermal signature and the accompanying hot spots on the PMIC vis-a-vis the SDRAM output of the PMIC. It opens up a whole new world.

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The mistake that lots of people make is that they always jump to the PMIC being bad just because it’s heating up and looks like it is causing a short but in fact it’s usually something down along the line that uses one or more power rails that the PMIC uses that are being shorted to ground by something else.

Check caps on VDD_main line, NAND 0v9 / 3v0 caps as well. What I do is remove them individually one by one until the short is gone. Do this one at a time so you can re-attach the cap back on and avoid needing to take one from a donor board.

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townsenj2000 さん、ありがとうございました！
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