Since a previous owner may have replaced the DMD chip on your set, the DMD board may not be aligned properly. This will cause a black band across the top or bottom. I've encountered this once, and it took me a while to figure out how to correctly re-align the dmd board to fix it. In my case the board that held the dmd chip was STUCK into position, so loosening the "adjusting screws" was doing nothing until I was finally able to free up the dmd board. Once that was done, I was able to re-align the dmd chip to the light tunnel and viola, all was well. I'll only add that MINUTE changes result in big movements on screen, and unless you want to run back and forth and back and forth (like I did about a dozen times) seeing what affect your tiny board movements are having, it's best to do this with two people. One to give you feedback on what's happening with the black band on screen, and you to loosen, adjust and re-tighten the board positioning screws.