As we know, if the iPhone screen keeps black after pressing the power button, generally there are two situations, one is the iPhone screen problem(black screen), and the other one is the iPhone motherboard problem(doesn't boot). First we need to check iPhone screen problem, after testing, we know it's the not the problem of the iPhone screen, the iPhone X won't turn on, we suspected that it was caused by the motherboard damage, we need to disassemble the iPhone X to check it.
Use screwdrivers to remove the two screws at the bottom of the iPhone screen, and then put iPhone X on the CPB screen separator, after heating for a while, we can open the iPhone screen easily.
After opening the iPhone X screen, we can see that there are not many areas inside the iPhone that are damaged by water.
Observing the iPhone X, we can see that there are traces of water corrosion on the right card slot and tail. Remove the iPhone screen and flex cable connector, connect iPhone to the DC power supply to check the current, the current jumps from 0 to 500mA. According to our experience, this situation is supposed to be short-circuited on the main circuit.
Remove the iPhone motherboard, and then observe it under the microscope.
It's found that the components around the iPhone Nand flash have traces of corrosion, use digital multimeter to measure the capacitor C2647, it's short-circuited. Open the ZXW Dongle to check iPhone X schematic diagram; we know that this circuit is connected to iPhone Nand flash and iPhone CPU.
Use QUICK 861DW hot air rework station and tweezers to remove the C2647, luckily, after removing the C2647, the current tested is back to normal. Check iPhone motherboard again under the microscope, the iPhone motherboard layer and other area are no corrosion traces.
Connect iPhone motherboard and iPhone screen, the iPhone X can enter IOS system properly, install the iPhone X to test other functions, after connecting all connectors, the iPhone X won't turn on smoothly, it automatically reboots after then white Apple logo appears.
According to our experience, it's the problem of the iPhone tail plug flex cable. Use digital multimeter to measure the iPhone motherboard tail plug flex cable, the resistance tested is normal, there are vibration connector and speaker on the iPhone tail plug flex cable. After removing the problem of these two components, we suspect that the tail plug flex cable itself is short-circuited.
Directly replace it with the new flex cable, and then install the iPhone X. Now test the iPhone X charge function and other functions, the charge function is normal. Power on iPhone X, other functions tested also is normal.