How to Deal with Half Backlight Failure

Backlight failure or Half backlight is common in iPhone 6P/6SP/7P/8P models because two sets of boost circuits are used in the backlight circuit of these models. If one of them fails, a Half backlight occurs, that is, only half of the backlight works normally.

First replace with a new screen to test, eliminate the screen backlight failure, then start to repair the motherboard

For example:

iPhone 7 plus backlight Half backlight failure

  1. First, test the pins of the screen link base J4502. According to the schematic diagram, the pins 37/39/41/43/45/47 are related to the backlight. Test the ground diode values of these pins and compare the point diagrams. If the measured values are normal, the base is not faulty.
  2. Measure the voltage value of the test points TP0411/TP0418/TP0419/TP0409/TP0410/TP0417. This voltage is the backlight circuit voltage.
  3. The test shows that the voltage of TP0411 is 16.97V, which is normal. The normal voltage value of TP0418 when the screen is on is 0.2V. At this time, 4.3V is tested, which is the voltage when the screen is off, which is abnormal.
  4. Since the test of the J4502 pin to the ground pole value is normal, there is no short circuit or open circuit. Therefore, it is judged that the TP0418 boost circuit failure may be related to the backlight IC U4601, or the inductor M2800.
  5. According to the analysis of common failures, the U4601 has a higher probability of occurrence, so replace it.
  6. After the replacement, the screen is turned on and tested, the backlight is normal, and the fault is resolved.

 

Repair skills

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