Malfunction Phenomenon
The iPhone X black screen and no response at all.
Trouble Shooting
Take apart the phone and run the cosmetic inspection of the motherboard. There is some deformation on the motherboard.
Since the issue is related to the display. So, we can measure the diode value on the display connector J5700 first, the measured diode value of pin 21 on J5700 is large than the normal value.
From the circuit diagram, pin 21 on the J5700 is connected with pin A6 on the CPU by way of L5720.
First, we can change the inductor L5720 with a new one. After that, measure the diode value again the issue still unresolved.
So we can detach two layers from each other and remove the CPU, and find the pad of pin A6 is missed. So we can conclude that the fault is related to pin A6 on the CPU.
Then we scrape out the relevant lines of pin A6 with a special knife and connected them with a jumper wire.
After finished it and put back the CPU, then assemble it and test again, the problem resolved.
