How do you have the board connected to? PVM? Old CRT? SCART connector? Svideo? Component? Or an actual arcade monitor?
Either way, you may want to test continuity from the source to the JAMMA edge. Also make sure your arcade board doesnt have a broken trace for the BLUE contact pad.
Most of the time there will be a broken connection from jamma connector and wire, however, you will not notice due to the heat shrink tape gives the appearance that it is connected. But it is not connected. You have to reconnect it.
Hope this helps,