sometimes screen goes black
I fitted a new display on the iphone 6 (quality tianma). perfect but sometimes after considerable use the display turns black for a few seconds. is a display faulty?
Probably is a bad display. Trying a different screen, possibly the old one if still available, will confirm this hypothesis.
From experience, it is something I've seen a few times with cheap screen assemblies.
Otherwise, the display circuit on the board may have been affected by the drop; or the proximity sensor cable is damaged (try a different one - this is a bit far fetched though).
My iPhone 5s have experienced the same case, but for my iPhone, i thought it's the storage probelm, as it's a 16GB iPhone.
The black screen problem can be fixed temporary by a restart. i say temporary, because it will happen again, after several days.
I finally fix my iPhone by cleanup all junk files and temporay files and get about 5GB storage back. Now i keep it have about 3GB free stroage space, and it works normally.