I will see if I can help, pac-man is a game I'm pretty familiar with.
It sounds like it could be a power issue, first thing to do is look here
http://lawnmowerman.rotheblog.com/ there are many fixes and things to help you fix your game here. I suggest checking your fuses/fuse block those are known to go bad and should be replaced. These cause all kinds of issues.
While you are in there check voltages going to your board, the website I listed gives tips on how to do that.
Pac-man is also known for having it's edge connector go bad so that may need to be replaced at some point as well.
The filter board is not needed and should NOT be used as it can cause more issues.
Fun fact - that little connector you mention at the side is a diagnostic port, I haven't seen it used for anything except this
http://cambridgearcade.dyndns.org/?q=node/44