As we know, there is a big difference between the touch circuit between the iPhone 6S and the iPhone 6. The iPhone Touch IC is integrated into the iPhone display assembly, and the iPhone display and iPhone touch IC share the same connector.
Try to fix it by replacing the iPhone display touch connector, remove the iPhone display touch connector, and then install the new one. After replacement, test the iPhone touch screen, but the iPhone touch screen still not working.
Check iPhone 6S schematic diagram by ZXW online account, we know that after the iPhone display and touch IC are integrated into the iPhone display assembly, the iPhone motherboard only provide the power、clock、reset、INT interrupted signal and SPI bus communication to the touch circuit.
When repair iPhone 6S touch failure, once the iPhone can be displayed after booting, we don't have to measure PN5V7_LCM_MESON_AVDDN、PP5V7_MESON_AVDDH and PP5V7_LCM_AVDDH, because these circuits are shared by touch and display.
In this case, generally we just need to use Fluke 17B+ Digital Multimeter to measure diode data for iPhone display touch connector J4200 some Pins, install the iPhone display assembly and turn on the iPhone to measure the voltage of the both PP5V1_TOUCH_VDDH and PP1V8 circuits.
Because the iPhone 6S has 3D touch function, if the 3D Touch function is abnormal, it also will cause iPhone touch screen can't be used. The 3D Touch is connected to the iPhone fingerprint connector, use digital multimeter to measure the diode data for the iPhone fingerprint connector, it's found that the diode data for AP_TO_TOUCH_RESET_L reset signal is smaller than normal value, it's only about 80, while the normal value is about 400.
Check iPhone bitmap, we know AP_TO_TOUCH_RESET_L this reset signal is connect to display touch connector.
However, the diode data for the AP_TO_TOUCH_RESET_CONN_L on the J4200 measured is normal. Continue to measure, it's found the AP_TO_TOUCH_RESET_CONN_L of the iPhone display touch connector and AP_TO_TOUCH_RESET_CONN_L of the iPhone fingerprint connector are not connected.
Use BGA Removal Graver to pry the black glue around the iPhone fingerprint connector, we found the FL4134 and C4134 and several components next to it all are corroded. Clean up the corroded components, and then install the iPhone.
Hope our sharing is helpful to you. If you have other better repair methods, please leave us a message in the comments.