Quoted from mkdud:
I would pull and test Diodes CR4, CR5, CR6, and CR7. I have seen these fail before; and the originals are about 40 years old.
I've bought quite a few Gulf repro boards before. They are pretty decent.
Quoted from vid1900:
I think that should be 12v on TP3, so if it's connected to gnd, that will blow your F3 fuse and you won't have 5v to boot from
I still don't get why the hell this jumper would even be here in the first place. Odd.
Thanks for the info fellas. I'll play around with it later and report back.