I have a few Segas with the supersize DMD displays, and most times the connector ribbon cable is the issue.

There is a new cable(upgrade cable) that u can purchase from Marco Spec or Bay Area Amusements which most of the time fixs the problem.

Here is the fix below - from Marco Spec

http://www.marcospecialties.com/product.asp?ic=500%2D6326%2D00

I added one to my Batman Forever and it fixed the issue