So I've spent too many hours to count restoring my prized Gottlieb Spirit and was almost ALL done with nearly no issues when I realized one of the controlled lamps on the Upper PF wasn't working. Given that I'm restoring the machine, I wasn't about to allow a bulb to remain non-functional.

Replaced light bulb. No dice.
Tested socket. All good.
Tested power to socket (with upper PF flipped upside down awkwardly). It was getting voltage but not grounding when it was supposed to.
Pulled the driver board and (ordered), then replaced the associated transistor. No change.
Now a second bulb that shares ground with the first bulb stopped working. WHAT?!!
This bulb now also was getting power, but not grounding either.

After fiddling for too long and pulling the upper PF too may times, I realized the socket for the initial bulb was flaky and was shorting internally to ground ...sometimes. I had tested it at first and all was OK. Moved the socket to replace the light with yet another new bulb (in case somehow I got two bad bulbs in there before) and tested again for the heck of it. Voila!

Take that, bad lamp socket!

It had been a six month process. I had the Pf professionally redone with touchups and auto clear. My cab was good but I spent some time touching it up. The machine has a lot of Mechs to rebuild and clean, etc. Took a lot of pics but still missed a few. Had a log, too which was helpful. Overall it had been fun. A few more minor things and it'll be all done.

I was happy to have figured it out, but was frustrated with the number of steps involved especially due to circuit board work. Gotta get out the tools, set it all up, etc. as I have no permanent workbench...though perhaps I should!

It probably would mean little to other people, unfortunately. Though anyone reading this is welcome to pm for pics they may have misses or questions about wiring, etc. I will probably have the pics for a couple years.