Hello,
I had a similar problem with my ms-pacman cocktail. I would get intermittent video but the game played on without a problem.
I installed a cap kit on both the monitor and the ms-pacman motherboard. They are a cheap and relatively easy fix to many problems (just be very VERY careful when working with monitors). However, while my image improved greatly, my intermittent video problem persisted.
Finally, I inspected the 2 pin molex connector that supplies power to the monitor. It had worn to a point where the connection was no longer reliable. I replaced that connector and haven't seen a problem since.
That's my story and it probably isn't yours but I thought I would share it for you and others.
Things you may want to try:
1) With game on, CAREFULLY turn up the brightness on the monitor until you can see a mostly white picture with lines on it. If you can see this, then your monitor is working but not getting a video signal. If you can't see this and don't hear the familiar high-pitched whine of a video monitor, then your monitor is dead and there could be several reasons. Search the web for a troubleshooting flowchart for the monitor type you have. It is most likely either an Electrohome G07 or a Wells Gardner monitor. A new cap kit and the replacement of the high voltage transistors on the chassis is a great way to start. Just do your homework if you've never worked on a monitor before.
2) If you can see the white lines when you turn up the brightness, then the first thing you need to check is the connection between the game board and the monitor.
The following web site has a wealth of information regarding Pacman/Ms Pacman and troubleshooting a restoration project.
http://users.adelphia.net/~68hc11/pacfile/pacfile.htm
A Ms Pacman board is just a Pacman board with a daughter card in the place of one chip. The problems are all the same between them.
Anyway, I wouldn't replace the monitor before you spent a little time first with troubleshooting the existing monitor. Most can be fixed easily and at very little cost as long as you take some time to learn and are safe.
Good luck.
