Most iPhone 7 touch screen faulty come from touch IC. Since its touch IC has been integrated on screen. This design is more likely to cause touch screen malfunction.
Touch issue on Logic Board IC has much lower probability, but it happens once in a while.
Today we are going to show you how to fix on logic board.
Faulty on logic board is generally caused by abnormal pins. The pin associated with touch screen is the eleventh pin of LCD touch FPC connector J4502.
In the first place, we need to test the pin’s power supply. Therefore we test its voltage. The normal voltage should be 5.1V; however, the true value is 0V. That is to say, this pin is abnormal.]
Has the touch connector been faulty soldered? We test all the pins’ diode readings, and then compare them with standard values. As a result, the touch connector has not been faulty soldered.
Faulty Pin Analysis
Check the circuit diagram.
U3703 is LCD Display Power IC, which supplies power for LCD touch FPC connector J4502. The power supply circuit is the faulty pin. Its code is PP5V1_TOUCH_VDDH.
We conclude from experience that U3703 has been faulty, which cause the pin faulty. So we try to replace it with a new one.
Fix Touch Screen
First of all, take off the faulty U3703.
Next pick up the new U3703 and BGA reball.
Then heat up logic board at high temperature and apply soldering paste.
Lastly, install the new U3703.
When we check the touch screen again, the touch function works perfectly.
Please check the following video for the detailed process: