If you own a pinball machine and you haven't been to the Pinball Repair site, your missing out. Full of useful guides, including everything from refinishing playfields and plastic ramp repair to the proper way to solder, it's an incredible wealth of information that is like no other site.
Partway down the main page you'll find a section titled Pinball & Coin-op Game Repair Guides. Within this section you'll find a link called Pinball Online Webzine. This link takes you to the repair blog of the Pinball Ninja, probably the most informative, respected, and documented pinball repair tech in the world. He shares a vast wealth of knowledge in photos and videos on how to fix all kinds of machine problems. His Bally/Williams reset solution is the gold standard - even other repair blogs refer to it. He only asks for a donation of $20 to subscribe, and I believe it's well worth for some of the repair stories alone! Although he used to refer to himself in third person with hilarious ninja euphemisms, he's toned that down quite a bit. Still, I'm almost always entertained by his repairs, and his documentation is top notch. Recommended reading.