Chosen Solution
I recently took my iPhone 6 apart in order to fix a sticky power button. Before I did this the screen was working perfectly and afterwards it is completely black, no backlight or anything. The screen definitely works works because I have tested it on a known good device and it is still fully functional. All the connectors on my device do not seem visibly damaged at all. When connected to iTunes the phone is recognised as being connected and acts as it normally should on the computer although the screen still remains black on the phone. Is there something I may have dislodged/broken/not put back together properly that is causing this issue?
The easiest thing to damage is the digitizer connector of the screen flex, if being pushed too hard plastic gets damaged and the connector gets bent. I’d suggest start checking that first and later all the small components around the connector on the logic board side. You will need good magnification and light.
