iPhone 7 won't turn on, how to fix it?

by Nancy N. DIY diagnostic and car repair tools

it is very common that your iphone 7 won’t turn on, you have to master the reason, that's mean why My iPhone Won’t Turn On? is software crashed or the battery charger problem? even is the logic board dead? today we will talk about the logic board is short-circuit on the iphone7 CPU, how to fix it?

First use the iPhone open tool to remove the iPhone and disconnect the battery, then connect the phone to the DC power supply, the current reading of the ammeter jumps to 350 mA and then remains still, which is an abnormality, indicating that the logic board is shorted.

Disconnect power and remove the logic board. Measure the capacitors around the power IC one by one. Except for C1823 all values are normal - 0 is displayed, which indicate a short circuit in C1823. Observe schematic with WUXINJI dongle, C1823 is the filter capacitor of PP1V8-SDRAM, which is directly connected to the CPU SDRAM.

Connect the logic board to the PCB bracket, use QUICK 861DW hot air rework station to heat shield cover, and then remove the CPU SDRAM with a CNC chip grinder. After grinding the chip, attach the logic board to the PCB holder and cleaned with PCB cleaner, and then the black adhesive is removed with graver scraper cutter. After that, apply BGA solder paste to the pads, and solder with a heat gun.

Connect the iPhone to a DC power source, then use tweezers to lead the pin 13 of the J4504 to ground to trigger system power. This time, the current read on

digital multimeter is normal.

Assemble the logic board. Connect your iPhone to your computer, then turn off the volume and enter DFU mode, insert your SIM card and activate your phone.

After testing all the functions work well. Repair work completed successfully.