Pacman arcade party video issue

[1supercomputertyler]

I have a coin-op pacman arcade party with 2 coin slots, the video output has weid dark lines that go across, slow down, stop, go away, and then go in the opposite direction. It's almost reminiscent of a sync issue. I tried connecting another vga monitor and see similar output. I almost wonder if it's phase and clock settings but they don't seem to fix it. Could this be a power supply issue or is this the gpu starting to go out. It has done this for several years but seems to have gotten a little worse. Any recommendations on how to diagnose

[grantspain]

it sounds like an earth issue or a capacitor failing on the monitor or even a power supply problem
can you connect an external monitor to rule that out

[lilshawn]

not sure of this one specifically, but other games I've had with symptoms like this where GPU capacitors are going bad.