Fast Repair iPhone 6S Plus Backlight problem

Since the size of iPhone6s plus display screen is large, it's necessary to use two sets of background lights to supply power, one is provided by U4020, the other is provided by U4050.

2 sets of circuit you can see from WUXINJI schematic diagram

1) PP_LCM_BL_ANODE, PP_LCM_CAT1,  PP_LCM_BL_CAT2 

2) PP_LCM_BL34_ANODE, PP_LCM_BL_CAT3,  PP_LCM_BL_CAT4 

For PP_LCM_BL_ANODE and PP_LCM_BL34_ANODE, if one of the circuit has no voltage value, it will cause the iPhone 6s Plus screen to be half bright and half dark.

For PP_LCM_CAT1, PP_LCM_BL_CAT2, PP_LCM_BL_CAT3 and PP_LCM_BL_CAT4, if one of  these four circuits gets abnormal signal, it will cause the 1/4 screen to be dark.

Solution: 

Use jumper wire to short connect PP_LCM_CAT1 and PP_LCM_BL_CAT2 or you can also connect PP_LCM_CAT3 and PP_LCM_BL_CAT4.

The control signals of these two sets of backlights, one group of inductors FL4211 FL4212 FL4213 are sent to the display interface. The other group is sent to the display interface through inductor FL4291 FL4292 FL4293.

These inductors are easy to get damaged and cause no lights or some parts are not bright, it can also solved by short connection. 

Check on schematic diagram, using an Fluke 15B+ digital multimeter to test 2 points voltage on iPhone 6s Plus circuit board, the voltage should be tested as 10V and 16V,  if the voltage is not normal, it means the U4020 or U4050 requires to be replaced.

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