I've had my head in one of these at one point... I recall them being similar to the Bally setup. There should be multiple large search discs, and as the disc is rotating, it is scanning the combinations of possible winners. When it finds one, it will hold that search disc in place while the user makes a choice.
bingobutch recently fixed one, and he told me that it operates a bit differently than expected... but I don't remember what he said.
I'd start by looking for the search discs and cleaning as needed. If they rotate in the same way as Bally games, there will be small metal hooks that sit in grooves beside the search disc. These are called slip rings and slip ring wipers. Those also need to be clean to transfer power to the search relays. Several search relays activated simultaneously will allow the search index (or whatever Keeney called it) to pull and hold the disc in place while the user makes a choice.
Some photos of the backbox interior would probably help, but it is likely going to come down to 'keen' observation without the appropriate paperwork.
You might check with Steve Young's Pinball Resource to see if he has a copy of the paper for it.