Could be the main or driver board ate it. Could be a tab fell off the on/off switch. Pins are a crap shoot just like vids, but with pins you need to make sure you're okay with the physical condition moreso than vids. You may never get a new playfield, translite, or plastics. Missing armatures, playfield toys, etc. may require a lot of patience to obtain. And troubleshooting all the electrical and mechanical issues it could have can be tricky (or nigh impossible) if you're not sure what you're doing.
I think with a Williams System 11 with some repro stuff available like Pinbot you're pretty safe. But, yeah, unless the condition of the wiring, cabinet art, playfield, toys, etc. is in good shape, $600 is a little much. Think more like $350-500 if in decent shape, would be less but Pinbot is a relatively popular title.
And keep in mind that once you're done with fixing everything to perfection you may end up spending at least that much again (if you can fix it at all without paying someone to). By the time I finish with my $1500 FunHouse it will probably have cost me at least $2500, more like $3500 if I go for a new playfield. My $2400 South Park ended up being more like a $3000 machine restoration costs included. But then not everyone has the inclination to make their pins 'like new' when they can settle for 'playable'.
Don't sleep on it too long though. Dallas/Austin/Houston can be tough cities to find good pins at decent prices unless MAYBE you hit the auctions. Too many retailers who buy, wipe the game down with a rag, replace the bulbs and slingshot rubbers, and mark up 400%.
