If the swap doesn't fix it, I have a very simple step that I would do next. Since it started to work for a while and then crapped, it sounds like you do have a bad connection somewhere that is vibrating out of place. I'd reseat everything on all boards and press on all seated chips. This simple step has saved me many headaches, particularly with this game. Even if this doesn't fix your current problem, remember this simple step when you have strange issues that come and go. After the reseat, I'd also move wiggle/move any connectors related to the graphics/DMD around in hopes of finding cold solder, loose connections or cracked wiring. If voltages are good and the swap is still bad, you have a bad connection or failing chip. Because it worked momentarily, my money is on a bad connection.