Malfunction Phenomenon
Receive an iPhone 7 no touch. Besides, the phone displays vertical lines on the screen.
Trouble Shooting
There are 3 main reasons that can cause the vertical lines issue.
- The screen is broken
- Power to the screen PN5V7 was abnormal
- The touch circuit was broken
Based on the repair rule. First, we can try to replace another screen and tested again, the problem still remains.
Then continue to check the display/touch connector J4502 by measuring the diode value. After measuring the diode value, pin 5 of J4502 was found shorted, the normal value should be around 1300.
Pin 5 is on the power line to the screen, PN5V7_LCM_MESON_AVDDN.
There are 3 components on this line between display PMU U3703 and connector, which we can remove one by one.
Remove FL3908 and check, the pad 2 is still shorted to the ground. This means the problem should come from the capacitor C3714.
Then we removed C3714 and measured the diode value on pad 1, the value was 1376, which was normal.
Replace C3714 and put back FL3908 and tested again, there are no vertical lines, and the touch function was back to normal, the problem was resolved.
iPhone 7 Motherboard Repair Course
