A while back, I got a Game Boy Pocket at a flea market. When I brought it home and tested it out, the screen had a few missing horizontal lines.

Fast forward a bit, I got a new one. The screen displayed fine, but was scratched up badly. So, I swapped out the internals (including the display screen), and put them in the other unit which wasn't scratched as bad. When I turned it on, bam, there was a line missing in the display. However, this one is vertical, right through the center.

What might cause this? I'm frustrated, since none of my handhelds have had borked screens before.