Chosen Solution
I smashed my iPhone 6. I do minor repairs on iPhones. I replaced the screen on my iPhone. It worked good for a while than touchscreen would freeze. ( home , volume, lock button worked ). I had to do hard rest to make it work again. I assumed faulty screen, then I tried and 5 different screens, but the results were same. Two days later I was in face time, than phone heated up and died. Than no matter what I do it wouldn’t turn on. No apple logo or nothing. Does anyone know what might be the problem. Could anyone reply the proper fix ( other than apple Genius Bar) I have all the tools necessary to fix the logic board. How can I test which component has gone bad.
This is a belated answer so hopefully it can be of use to folks who search for and find this question. In a case like this, the issue could be caused by a repair gone bad (it happens :>) or it could be caused by whatever impact damaged the screen in the first place (more likely). When dealing with a “dead” phone, there is no “silver-bullet” solution. You have to probe the board to get a better understanding of what is working properly and what is not. It may be a simple solution or a complex one. Sometimes we see a visibly blown cap, replace and all is well. Other times, everything looks perfect yet the phone won’t boot. The proper course of action is to do a good visual inspection (under magnification) of the logic board. Assuming everything looks good, then start at the beginning and check PP_BATT_VCC, PP_VCC_MAIN and PP5V0_USB. I would start by checking to see if those rails are shorted to ground. If one of these rails is shorted to ground, then you will need to identify what is causing the short. It could be a bad decoupling capacitor, conductive debris or defective IC that is directly supplied by those rails. If they are not shorted, then you can connect, preferably, a known-good battery (or a current limited DC power supply with the appropriate connector adapter) to see what voltage you measure. If the voltage is low or lower than the battery voltage (which you measured before plugging it in ;>), then there could be a short circuit on secondary subsystem that is causing the battery or DCPS to be current-limited. If you are measuring the proper voltage, then you move onto the PMIC and check the voltage rails it generates. The PMIC generates ~15 voltage rails. They are all important (for obvious reasons) but the ones to check first are as follows: PP_CPU & PP_GPU – These rails supply the CPU & GPU. They are low resistance rails so they may “beep” when you test them on your multimeter in continuity mode. It’s important to look at the reading and not focus just on the beep. You will typically measure something around 20-100 Ohms on these lines.PP1V8_SDRAM & PP1V2_SDRAM – These rails supply the SDRAM (which is sandwiched with the SoC/CPU).PP_VAR_SOC & PP0V95_FIXED_SOC – These rails supply the rest of the System on a Chip. What we commonly refer to as the CPU is actually a SoC.PP3V0_Tristar & PP3V0_NAND – These rails supply Tristar & the NAND chip.PP1V8_ALWAYS – This is an “always-on” voltage rail that is used for the bootstrapping of the devicePP1V0 – Supplies the High Speed Digital Communications via the SoC From there, you check the remaining lines and then move onto the Baseband PMU if necessary.
