Malfunction Phenomenon
Press the power button to power on, the Face ID function can’t work normally. Besides, the rear camera can’t work neither.
Trouble Shooting
Take apart the phone and run the cosmetic inspection of the motherboard. After checking, the cosmetic of the motherboard is in good condition.
For the iPhone X Face ID Not Working issue, the fault is related to the rear camera. Firstly, we need to measure the Tele–camera connector J4000, the measured diode value of pin 27&pin28 is 1700, which is larger than the normal value (normal value is around 820).
According to the circuit block diagram and the bitmap, the fault is might be caused by the false solder of Q3700.
So we can try to resolder Q3700, then make the upper layer and lower layer solder together, and assemble it and test again. After that, the problem resolved.
Tips: In this case, there is more than one issue. So we need to check the problem which normally would be easier to fix.
Here, we measure the diode value for the rear camera connector first.