Chosen Solution
Hi, Newbie here, just on my third iPhone repair (microsoldering) and wanted to get your feedback before I take off the PMIC and replace it. I have a water damaged phone here, upon first inspection and after cleaning it didn’t look so bad, but it was dead as a doornail. AMmeter does show 0.5a when I plug the logic board in (new battery, new dock connector, new screen). No sound/image though and the PMIC gets hot real fast. Measuring caps along VCC main revealed a short to ground on C1200. I replaced that with a known good working one from a donor board, but the short is still there. Seeing as PMIC gets hot as well, I think it’s that that needs replacing or do you gurus have another thing I can try before I go that route ? Thanks in advance for any tips ! Major update : Turns out I was looking at the wrong spot the whole time. I thought the PMIC was getting hot, but in reality it was the CPU, a lot of caps near the CPU top row were also shorted out. Measured D1501 diode and only came out on 0.002, so the backlight diode was (one of the culprits), I suspect the backlight IC itself is also faulty. and maybe even the coil. I’ll order a set of those and give it one last try. I didn’t think it would be ‘just’ a backlight issue, since I tried shining with a heavy duty flashlight through the back of the lcd and nothing appeared, but I guess a faulty backlight coil/ic/diode could cause these symptoms ? This is really a rabbit hole, I don’t think I’m a big fan of waterdamage repairs :)
Update : removed the backlight IC, the filter, coil and the backlight diode (since I ordered those to be replaced anyway). The shorts are still here. So no use in replacing the backlight parts. At this point I have no idea anymore where to check for shorts (thinking it might even be a short underneath/in the cpu itself), so I’m giving up on this one. Better luck next time ;) In the meantime I’ve been learning to use PADS. Can any of you pros give me a reason why I should buy the Extended version instead of keep using the free PADS X2.1 viewer ? It can handle the iPhone .pcb-files just fine, and with F5/F6 I can see which components link to which points/components. Thanks Minho, you’ll probably see me around here in the future :)
There are a lot of caps on VCC_MAIN, you pretty much have to test them all until you find the bad one (if that’s the problem). The PMIC getting hot could be either the PMIC or a (or multiple) shorted line(s). Given that this is a water damaged phone, you really should test all of the voltage lines it drives to see if something downstream is pulling everything else down with it. First check to see if they are shorted and then test actual voltage. Caps are a likely failure point but an oxidized IC anywhere on the board can also cause a short on VCC_MAIN. Water damaged phones are the toughest to troubleshoot because there could be multiple issues stemming from anywhere on the board. If the water damage was minimal and localized, you could focus your efforts there but otherwise, you will need to start at the beginning.
