I took apart my Gameboy Color recently to replace the housing, but when I put it back together I noticed a small black bar on the top of the screen, it bugged me enough to ask if I had broken it, or is the case not a good fit for the screen?
Make sure the ribbon cable is pushed in all the way, or else it can result in small dead pixels like that, but pushing the cable in all the way should get rid of it.
