Chosen Solution
Hi guys, I have an iPhone 7 Plus here with a broken screen. According to the customer, the phone powered on when he put it on charge. The screen was broken, so my job was to replace the screen, an easy job. I trust the customer, so I didn’t turn on the phone before going ahead with the repair. As usual, I disconnected the battery before removing the broken screen. To my surprise, the phone is completely dead after I installed a new screen. Tried a good working battery, still dead. Tried another screen, still dead. No dim logo whatsoever, just dead. When connnected to power supply, as soon as I pressed the power button, I even didn’t need to hold it, as soon as I pressed the power button, it jumped to max 1000ma, and stayed at 1000ma. It showed that somewhere on logic board is shorted. I tested all the caps, however, I couldn’t find any short on board, the PMIC however was getting very hot. Can anyone suggest where to test next? The PMIC is quite difficult to replace, is there anyway to prove that it’s faulty? I really don’t want to touch the PMIC unless it is indeed faulty. Update (01/29/2019) I believe I found the issue. Using deep freeze, one corner of the PMIC is the first to melt. Unfortunately it’s the PMIC this time. :( I don’t understand why replacing the screen will cause the PMIC to be shorted!!
It’s pretty rare that the PMIC is the root cause. Before you start mucking around with the PMIC, you need to figure out which line is actually shorted. Probing caps haphazardly doesn’t always identify the problem, you need to take a more systematic approach. So open up your schematic, find the PMIC page and check each output , one at a time, until you find the short. Once you’ve identified the short, you need to determine if the issue is with the downstream circuit or the PMIC. On some outputs, removing the coils helps isolate the two sides of the circuit. For the LDO outputs, you have to start removing the caps one at a time. Of course, once you know which line is shorted you can use freeze spray again and focus only on that line.
