In iPhone 6 repairing, we usually see that the uneven brightness problem which the four corners or one side of the screen have darkness has a strong impact on the usage of iPhone. The effect of the screen still keep the same after we change another screen, so we can affirm that the uneven brightness problem is caused by the damage of mainboard.
Inspecting the screen, the right side of the screen has darkness. It is estimated that there is a problem in the right side connecting circuit of the backlight, which is also the connecting circuit of the fourth pin of the LCD connector.
Using the multimeter to inspect the value of resistance to ground of the capacitor C2018 with diode gear, the red pen connects the ground and the black pen tests the value, the value is normal and function is well.
Using the multimeter to inspect the inductor FL2025, the first pin resistance to ground value of FL2025 is about 600 ohm which means U1502 is in good condition. The second pin resistance to ground value of FL2025 is infinity which explains FL2025 is disconnected and uneven brightness problem occurs.
Installing a new inductor to the mainboard or connect with solder wire.
Installing the screen to the mainboard and test it, the screen is ok.
If the left side of screen has uneven brightness problem, you can check the left side connecting circuit of the backlight, which is also the connecting circuit of the first pin of the LCD connector. Inspect the function of capacitor C2019 and inductor FL2026 and repair the damaged part of them.
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