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My iPhone suddenly stops working and when I pushed the lock button it asks to connect to iTunes .so connected to my laptop to do restore but it failed! so I tried again but now the laptop wouldn’t detect my iPhone and now its dead. then I went to repair shop he said “I changed the power ic and it worked but when I tried to restore it went dead!” he said it cant be fixed the problem in the CPU. I don’t know if he was honest with me so I tried to troubleshoot by myself. I connect the iPhone to the power supply with 3.8v when I pushed the lock button it read constantly 0.2 amps. the battery voltage was 2.6v but after charging it became 3.7 v I connect it to the USB charger and measure the voltage on the battery connector it was 3.7v I tried to do some measurement depending on the schematic but I don’t know where to start. but I noticed that the test point TP1120 which I suppose connected to the PP_GPU read 0 v .and the multimeter beeps when I put it on the beep mod! so is the PP_GPU shorted? any idea what to do next? and how to test the PMU? I’ll be grateful for any answer
PP_GPU only activates when the screen is used, so it will read 0V if the screen isn’t turned on. As for beeping, PP_GPU (as well as PP_CPU and a few other lines) are low resistance lines. They will cause a multimeter to beep but they are not shorted. They typically measure anywhere from 20 Ohms to 100 Ohms and that’s low enough for most meters to “beep” in continuity. If the shop has already tried changing the Tristar IC, then hopefully they have done some additional troubleshooting to come to the conclusion that the problem is with the CPU. If all they did was shotgun replace Tristar, then you should seek a second opinion.
