First, confirm whether there is a problem with the home button cable. If the cable is broken, perform a jump wire repair on the home button cable, otherwise, the Touch ID will be lost
After troubleshooting the home button cable problem, enter the motherboard repair procedure.
After cleaning the fingerprint interface, measure the ground resistance and voltage of each pin of the interface. After finding the abnormal resistance or voltage, measure the ground resistance of all the originals on the same line according to the schematic diagram to find the problem.
iPhone 6S’s Back button interface J4100
From the schematic diagram, you can know the resistance of each pin to the ground and then test them. If the resistance of each pin is normal, the interface has no-fault
Test the pin voltage after power-on and start, and look for abnormal pins according to the schematic diagram.
In this example, the voltage of pin 21 is abnormal, it should be a 16.5V boost circuit, and the actual measurement is 4V, then according to the schematic diagram test to find this circuit abnormality.
The interface upper-level chip, MESA IC U4010, tests the resistance to the ground of the chip circuit supporting capacitors C4041 and C4043.
If the capacitance test is normal, the boost IC is faulty, replace and repair it.
After replacement, the test that the voltage of pin 21 is normal. Install the screen and test, the Touch ID is normal
iPhone 8 Plus’ return key interface J5800
Test the resistance of each pin of the J5800 interface to ground, and the test found that pin No. 2 is short-circuited to ground
According to the schematic diagram, the fingerprint 3V power is supplied by pin No.2. If this circuit is short-circuited, it may be a component short-circuit, or the power supply IC U2700 is faulty.
Test the capacitors C5803, C5804, etc. on the circuit, find short-circuit capacitors, and replace them.
Re-test pin No. 2, the resistance to the ground is normal, and then installed the screen and text. The Touch ID is normal.