Here is the guide of the iPad screen
displays abnormal, the right backlight shows dark but the other half is normal.
This guide will help to fix it. I hope you won't use it, but in case, it's
useful for you.
Two backlight circuits control iPad 4 and
according to our experience, this problem is obviously caused by one of the
backlight circuits abnormal power supply. Analyze the circuitdiagram, we know that main power supply management chip U8100
outputs the two backlight power supplies PPLED_OUT_A and PPLED_OUT_B, as shown in
picture 1-1.
1-1
After the two backlight power supplies are
renamed, they are converted to PPLED_REG_A and PPLED_REG_B, as shown in
picture 1-2.
1-2
After they go through inductor L2210 and
inductor L2200, they are converted to PPLED_BACK_REG_A and PPLED_BACK_REG_B,
and sent to display screen socket, as
shown in picture1-3.
1-3
These power supply circuits are directly
connected through inductors and we can measure the diode data of display screen
socket to analyze the problem. When we measure the diode data of
PPLED_BACK_REG_A, we find that the data is much larger than that of
PPLED_BACK_REG_B, as shown in picture 1-4
1-4
Finally, observing under a microscope, we can see the obvious fault
location. Around the inductor L2200, we find the marks of tin explosion, as
shown in picture1-5. Use a multimeter to
measure the inductor and it disconnects. Replace this inductor and test it,
iPad screen display normal, the entire screen is light.
1-5
The related video link: https://www.youtube.com/watch?v=GTOSC6hGIAc
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