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half backlight , O/L diode mode reading on pin 35 of J4502

Hi , i have this iphone 7 with half backlight issue , i replaced U3701 but it did not fix the issue , I have an O/L diode mode reading on pin 35 of J4502 , FL3902 on this line tests ok , I have removed U3701 and lines from pads A1 and B1 seem shorted together .

I’m a bit stuck now ..

Hi , the phone originally had no or very glitchy touch and had no 5 volts on pin 11 of J4502 , the components on that line seemed ok so I replaced U3703 it still didn’t fix the touch , still no 5 volts on pin 11 .

After that I had the half back light issue , you were spot on with the diagnosis for that ,after scraping the underfill away FL3903 and FL3901 were indeed shorted , the backlight is good again now ..

I’m not sure how replacing U3703 caused that short as I didn’t heat that part of the board and they are heavily underfilled .

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Posted: Jan 24, 2021

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I am not sure why you removed U3701 half backlight would not indicate that it is faulty with OL on pin 35. This has only added variables to the repair. You need to follow the PP_LCM_BL_CAT1_CONN from the connector to U3701. Check the connector pad and not just the pin.

You say that Fl3902 is not faulty. What is the diode reading on both sides of the pads? If the PP_LCM_BL_CAT1_CONN line is continuous to U3701 the only thing that would cause OL on pin 35 would be a missing or damaged pad at (C1) under U3701.

The only time I have seen A1 and B1 shorted together is when other components have been bridged like FL3903 to Fl3901. Check very closely under your scope.

Remember the more things you try and replace on this repair will cause more variables. Make sure the component you remove is indeed faulty.

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iPhone 7

half backlight , O/L diode mode reading on pin 35 of J4502

Update (01/26/2021)

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