I totally LOVE reading these EM repair threads. Since multiple Tim's have chimed in, I'll do the same...
I'm new to EMs as well, and I have gone through the kind of situation you did in August. My Space Odyssey went for 13 days without working properly due to 2 separate issues with leaf switches. One was fused shut and just needed some cleaning from a flexstone and the other was bridged by its leaf stiffener causing the switch to be "made" at all times. Both problems were caused by my own attempts to "fix" other issues.
*The fused contacts were on my Tilt Relay. This was causing the game to be constantly in "Tilt" and cutting power to all my playfield scoring.
*The bridged switch caused by the bent stiffener was on the ball eject switch. This meant that the circuit was being told that the ball was still in the drain hole even after the solenoid had kicked it into the shooter lane.
So I had a game that was not scoring AND the ball eject solenoid was firing over and over every time I turned the sucker on and started a new game. However, this situation (as those with more experience than me likely could have EASILY seen and backtracked through) was causing the score motor to work through the reset sequence over and over again when I fired up the game. It was driving me absolutely nuts and I reached a point where my frustration led me to just give up. At that point, I told myself that I wasn't going to ever be able to fix the thing and I was on the verge of considering calling in a tech or whatever to get the table working again. All I can say is that I'm glad I didn't. Why?
Because it was only by settling down, taking a breath and listening to some great, helpful people on here like chrisbee and SteveFury that I got to the bottom of the issue. I had gotten myself so worked up, being new to the hobby, that I was forgetting exactly what so many people have said in this thread - it is usually very logical and basic with an EM. Settle down, reference the schematic to find out what switches and relays are "in play" for the specific issue, and methodically work it through. It was a huge lesson for me to learn and I'm glad I stuck with it.
Glad you're up and running again! Every time you (or me or anyone else new to this) take the time to work the logical steps out and find the source of the problem, it makes you that much better at EM repair. It amazes me what I've learned in my first six months with my machine, and hopefully you're feeling the same way. I feel like the confidence gained through sticking it out and fixing such issues makes things less stressful down the road when other issues pop up.
Tim in Motown