Repair iPhone 6s can't add fingerprint failure

The iPhone 6S accidentally dropped into the water, and then it came up with a fingerprint faulty, the iPhone 6S can't add fingerprint. So the customer sent it to us to repair. Now, let's take a closer look at this iPhone and then repair it!

Disassemble the iPhone by JM-P01 Toolkit, carefully remove the iPhone motherboard. After checking, we found signs of corrosion in the fingerprint socket, and then detect MESA_TO_BOOST_EN_CONN.

Use Fluke 15B+ Digital Multimeter to measure the diode data of PP16V5_MESA_CONN fingerprint boost boot signal and 16.5V, the data is normal.

Observe the iPhone PCB board carefully under the VGA Camera 7-45X Trinocular Stereo Microscope, we found something else. The bottom pin was severely corroded after the corrosion was removed from the fingerprint boost U4040. A2 pin PP_VCC_MAIN is disconnected, and the A1 pin CND close to PP_VCC_MAIN is dropped by corrosion.

Soldering the jump wire on A2 pin via Quick 861DW, but the fault still exists. Why is there such a problem? There are no problems anywhere else, L4040 boost inductance is normal after checking.

We have to rearrange the repair ideas, and then re-check it. Most of the time, we're only one step away from fixing the iPhone, it depends on the details. Open the WUXINJI Dongle to check the iPhone schematic diagram, we found this boost IC bottom pin only has two GND.

Someone would say, the ground is interlinked, that's definitely not a problem. The iPhone motherboard GND must be connected. However, after measuring, the two ground of IC bottom pin is disconnected, which means these two are indispensable. If one is missing, it will cause U4040 not to work. After weld the jump wire, the problem of fingerprint that don't have 16.5V has been solved.

Install the iPhone and turn on it to test, the fingerprint entry is normal, now you can add fingerprint on your iPhone. Test the other functions, all is fine.

Summary

Fingerprint bottom pin GND cannot be ignored, because it can cause U4040 IC not working. During the repair process, you can ignore any place that might cause problems. Just be careful and patient.