We received an iPhone 7 recently from a regular that had done water damage treatment on the client’s device. After cleaning there was still no image.
We checked this and there was an image but no backlight. We removed the board and checked for blown filters and shorts on the bottom of the board on the backlight circuit. We found FL3901 had blown and there was some corrosion on capacitors around this area. We checked voltage going into FL3901 and found a very low reading. We tested at D3701 and found the same which meant that the backlight IC was not outputting the correct voltages.
We removed the blown filter and replaced with a new one and then removed and replaced the backlight IC. After doing this we checked for shorts around the backlight and image circuits and all seemed clear. We tested the device and the screen came on as it should. We tested all basic functions as this phone was originally water damaged and no further faults where found. We reassembled and returned to the customer who was very happy to have a working phone back.