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Released September 16, 2016. Model 1660, 1778 Available as GSM or CDMA / 32, 128 or 256 GB / Rose gold, gold, silver, black, and jet black.

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iPhone 7 (intel) A1778 no backlight troubleshooting help

hello. i have an iphone 7 logic board that does not have backlight, i put it in a functioning iphone 7 with a functioning original screen and the backlight does not work (i can see the apple logo and the hello (i yet have to activate this one))

my troubleshooting: i put in the usb powermeter and it draws 1.5amps, tried to boot and i hear vibration and sound. connecting to itunes/3utools i get detected. so i checked with torchlight and see that it has display but no backlight

further troubleshooting: i took off the motherboard and checked with multimeter the J4502 connector pins 35 37 39 with diode mode with the red on ground and got 0.6v on each of them, i went further and check the with diode mode the 3 filters (fl3901, fl3902, fl3903) and all 6 pins had a reading (something like 0.59v).

i have done also the diode mode from tp0409 to c3904

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from tp0410 to c3905

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and from d3702 to c3725

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and got 0v, which i think should be alright ( the start of the arrow in the img is where i put the red probe of the multimeter)

now: i am stuck, i dont know how to further troubleshoot this. i have a pretty cheap microscope for visual inspection, and seems to me that the c3903 is missing, but watching many many videos of iphone7 backlight repairs seems to me that the c3903 is missing everywhere (or i cant see because of low quality video). i also have some iphone 6, 5s and 5 donor boards, and a hot air station (no soldering iron yet. though is on its way, arriving later this week). if there is a way to maybe grab a missing component from these boards i am happy to do so

does anybody have an idea on how should i go further?

many thanks for anyone

edit:

further testing: i opened the good iphone logicboard, and checked if there is the c3903 capacitor and it seems to me that there is not

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1 is c3939

2 is c3905

3 is where in the schematics the c3903 seems to be

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How did you get voltage in diode mode.

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On j4502 what diode readings do you get on pins 35, 37, 39. Red probe on ground.

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pin35:

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pin37:

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pin39:

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i said volts because i see the V in the upper of the screen

the board is outside of my phone, nothing connected to it

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Have you tried changing u3701

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not yet. i’d like to be have a bit of confirmation before i start swapping chips. but everything points there, i will swap it tomorrow morning if no other solutions arrive. ty

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ok i swapped chips and now it doesnt draw current, i think i fried some components. the chip took sooooo long to get out (used 320-350 celsius) for i think 2-3 min. it’s midnight here, tomorrow morning i will do other troubleshooting, for more problems.....

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Gyca Popescu zal eeuwig dankbaar zijn.
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