Fault description: iPhone 5S fingerprint happens intermittent faults
We may need to disassemble it and get the home button, check whether the IC happens fault, then let us start.
First we need to check iPhone 5S fingerprint schematic diagram in WUXINJI Dongle, there are three 3 sets of power supply circuits mainly, they ware 1.8V, 3.0V and 16.5V, the 1.8V and 3.0V are available after booting.
When press the iPhone power button, the 1.8V and 3V can be measured on the fingerprint socket by Fluke 15B+ Digital Multimeter, and can be measured on the interface J7.
The 16.5V cannot be measured at ordinary times, it can only be measured when the finger touch the iPhone home button to add a fingerprint or when unlock iPhone with fingerprint.
There are two cases of fingerprint failure, one is failed to open the "add fingerprint" icon, and the other one is "add fingerprint" icon can be opened, but it has no response when you touch the iPhone home button with your finger. The first case is caused by abnormal 1.8V or 3.0V or damaged iPhone home button, the second case is caused by abnormal 16.5V.
According to iPhone schematic diagram, we know that the FL33 easily corrode and cause 1.8V failure, and then causes iPhone fingerprint failure, we can fix it by short connecting. Furthermore, the U1700 is a 4 pin glass tube and it is easy to damage, so the 1.8V can't be outputted, and causes fingerprint addition failed, we can use tweezers to remove the U1700 and then short connect A1 and A2, as shown in picture 1-1. The 3.0V is supplied by iPhone power IC, iPhone power supply IC output 3.0V power supply PP3V0_NAVAJO via FL19 to interface J7, FL19 is easy to corrosion, and caused no 3.0V, so the iPhone fingerprint will be failed，we can fix it by short connection.
The 16.5V is supplied by U10, U10 output 16.5V power supply PP16V5_MESA via FL54 to iPhone tail plug flex cable J7.
FL54 is easy to corrosion and caused PP16.5V can't be sent to fingerprint interface, we can use QUICK 861DW hot air rework station to short connect it. U10 also is easy to damage; we can replace the U10 to fix it.
Then assemble it again, try to reboot the iPhone by home button with volume key, you will get the answer.
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