I've learned it's the simplest things.
Messing around with various options for why Solar Ride wouldn't coin up, and it boiled down to a failed connector from the power supply 5V to the MCU. Luckily it wasn't the -12V when that happened during a game for the original owner.
Sometimes it's better to just order a replacement part, then try to repair the original part. I've still got the original power supply for Solar Ride sitting off to the side of my workbench, although I'll probably just pop the new parts back off of it and consider ordering a brand spanking new power supply.
When something starts going wrong, power down immediately and figure out where the problem is. When you smell something distinctly non-edible (like plastic) cooking or burning, again power down immediately and figure out where the problem is.
In other news, coils trying to pull to stop and failing to move will not only get very hot very quickly, but will also make their mounting hardware very hot as well.
3 days is a long time to not have a working pinball machine.