Chosen Solution
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
from tp0410 to c3905
and from d3702 to c3725
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
1 is c3939 2 is c3905 3 is where in the schematics the c3903 seems to be
On j4502 what diode readings do you get on pins 35, 37, 39. Red probe on ground.
pin35:
pin37:
pin39:
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
