Hi Redcloud . If you work on something as complex as clocks, then I have high confidence that you can figure out an EM. I treat them as a bunch of little puzzles to solve.
I am an electronics geek, but here are things that helped me:
http://www.pinrepair.com/em/index1.htm#top
Search pinside for your game and look at the forum posts tab — you might find your exact problem. You can also use google to search.
Post your problem on pinside and tag your game. There are lots of folks who can give you suggestions.
Use jumper cables with alligator clips to eliminate or “force” conditions in the circuit to narrow down the potential switches/relays.
Build a test lamp with 2 12 volt bulbs in series and clip leads wired to the other bulb terminals. This helps to visually show you what parts of the circuit are energized in a gottlieb or Williams 24 volt machine. Bally uses 50 volts so this tool doesn’t work there.
A pinball machine is a big state machine. It starts in one state, switches and relays then cause it to move to a new state. That doesn’t get shown on the schematic and it takes a while to get the gist of that.
A schematic is a logical representation of the circuit, not a physical one, so that can lead to a bit of confusion when you’re looking at the physical wires.
A short circuit won’t be shown on the schematic. Sometimes weird behavior is because of a connection that isn’t supposed to be there. 2 solder tabs touching, a bare wire touching, or a make-break switch that is touching both terminals at once can screw stuff up.
If it’s a machine that’s new to you, odds are that a fix or hack made by a previous owner needs to be done properly.
I hope this helps. It is a fun and rewarding hobby.
Dave