Response from Jonathan: Steven,

Actually it sounds like you’ve done a lot of great troubleshooting already. By replacing the monitor with a known working one, you’ve basically narrowed down the issue to your Double Dragon board. Ribbon cables are notorious failure points for arcade boards so cleaning, reseating and replacing them is always a good idea. Keep in mind that it could still be an issue with the wires going to your monitor so make sure you check those out (and the connector they are going into) as well. Also, you might check out our post on Inspecting An Arcade Board for some helpful tips on troubleshooting board issues.

Other than that, it’s probably an issue with some components on the video board. You can find the schematics for the board on the MAMEWorld Forums. Those should help you at least figure out where the problem is with your board. If you’re not familiar with schematics and board repair, you might consider contacting one of the people under the Board (PCB) Repair & Component Sales heading on our resources page as these people specialize in this area and should be able to help you with your issue.

Hope that helps. Thank you for your question and good luck with your repair.