Chosen Solution
So I picked up an iphone XR, and the screen wasn’t working. When it turned on, only a faint white light showed and nothing else, but the phone was still working (vibrating, iTunes/3utools detects it). So I bought a replacement screen, followed the ifixit tutorial, and reassembled the pieces onto the new screen (as far as I know exactly like it should’ve been), and connected the 3 flex cables to the phone and tested it before screwing everything back into place, but the screen didn’t turn on, and also didn’t have any faint white light showing. But the phone was still working. I tried restoring it, hard reset but still nothing on the screen. So then i replaced the parts from the replacement screen, and putted it on the old screen, but this time it was also completely black and not even the white light was showing. So what could be the issue here? I guess it has to be a hardware problemen, but wich part? The screen itself or the earspeaker? Thanks in advance!
You have ruled out parts and backlight and confirmed it is an image problem. The next step would be making sure the display connector has no bent pins and the connector is seated properly than use a multimeter in diode mode and test the pins on the logic boards display connector. You will be looking for an open or shorted line. Once you have found the faulty line you can trace it back to the failed component. I would mention that to fix this issue will require microsoldering skills and equipment plus board view software.
