The monitor is fine. Since no one had this problem with a Frogger board, I looked for Galaxian boards with this problem(since they share the same video hardware) and found that someone had this problem and fixed it by replacing the octal transceiver that talks to the VRAM.
Repair log(not mine): http://wiki.arcadeotaku.com/w/Galaxian_Repair_Logs
Hopefully replacing that chip will fix the problem.