Great to see you have it home "safe and sound". Looks like a great machine to add to the gamesroom.
Could simply be a microswitch issue, or if the joystick is a two way, it might be the leaf switches. Either will be on the joystick. Look for a loose wire.
Did you get original documentation ? There should be a dip switch for "cocktail mode" - depends if the board is original or a copy. I have some documentation I will check tomorrow.
Pete - Please be VERY CAREFUL around the monitor. There's some high voltages that you don't want to mess with.
There are not many techs that look after these old machines - it depends on the issues that you have, they might be a simple adjustment. Can you take a picture of the screen and describe the problems ?