I go through all of the contacts tightening relay stacks, burnishing the contact faces, and verifying proper wipe. It's amazing how many defects you will find when you look at everything.

I just followed this approach on an El Dorado and even then it wouldn't start. One switch I had not gone through was the coin door slam tilt switch wasn't making. Ohmed it out and found it and adjusted it and the game played 100% after that. Still needed a few adjustments but everything worked.

It's much easier to chase down the exceptions when you know the game has already been gone through.