iPhone 7 No Backlight But Display Can Work
Malfunction Phenomenon
Press the power button and boot, we can see a faint apple logo on the screen.
Trouble Shooting
Normally, there are 3 situations can cause this kind of issue.
1. Related pins on display connector J4502 was corroded or dirty things on the pin;
2. Backlight IC U3701 or combined inductor M2800 or components on the rail was damaged;
3. The related rail was disconnected.
We measured the diode values on pin 35, pin 37, pin 39 of display connector J4502.
These 3 pins are related with backlight as we checked in schematic.
Pin 35 PP_LCM_BL_CAT1_CONN
Pin 37 PP_LCM_BL_ANODE_CONN
Pin 39 PP_LCM_BL_CAT2_CONN
The diode value on pin 35 & pin 39 were normal, but pin 37 was abnormal, it shows “1”, which means diode value was infinite.
We followed Pin 37 to check the components on the line according to bitmap, and we found the line between FL3901 and J4502 was disconnected.
Pin37 and FL3901 are in different sides of the motherboard, it’s difficult to jump wire on the connector. We checked the motherboard again, there is a test point TP0411 connected with pin37, we jumped wire from TP0411 to FL3901 directly.
After we jumped wire, we tested, backlight was back, problem was resolved.
