I’d recommend starting with the bingo repair videos. I’ve watched both videos three times. If you know as little as I did (some would say, still do), it is money well spent. It helps if you compile your own table of contents as you watch the videos. For example, you might record “Search Disc - volume 3, about the 5.23 minute mark.” It will save you time when you need to go back later for a refresher.
Alan Marriage video:
ebay.com link » Bally Em Bingo Pinball Machine Service Dvd Video Volumes 1 2 New Sealed
Richard Gerlitz video:
ebay.com link » Bally Bingo Pinball Repair Course 11 Total Videos Get Your Game Running
The Gerlitz video is better of the two, but it’s useful to see two guys who both know their stuff explain things their own way.
Phil Hooper’s web site has the most detailed explanation of bingo circuitry you will find. Start with the “How They Work” section. Make sure you have a bottle of scotch so you can follow along in full fidelity:
Ask questions here on Pinside, you’ll get plenty of help.
Check out the Bally Bingo’s in Britain forum. There are lots of knowledgeable and helpful collectors there, many of them European: