Anything tilt related you usually suspect the slam tilt switch, although this doesn't sound like it.
Firstly, check the one on the door though - it is normally closed (ie opens when slammed), slide a business card through the contacts to clean any much out.
You can do the same with the one at the captive ball near the plumb bob, and of course check the plumb bob hasn't come loose.
Try after that, then if still a problem, reseat all connectors, that's a common problem of course with these old games. If connectors, might need to think about re-pinning.
