PCBS with known issues added to first post:
PCBS WITH KNOW ISSUES ON THE CBOX:
Mortal Kombat 1 (worked fine but seemed far out of spec) @mathewbeall
Mortal Kombat 1 (had the same issue as before with extremely dim screen (almost black) and -6.6v on the -5v line) @djsheep
Killer Instinct 1 (Unknown?) @mathewbeall
USAAF Mustang (reading of 12.7v on the 12v line) @djsheep
Thunder Zone (13.2v on 12v) @djsheep
Sorry, but every PCB displays higher voltage on the 12v line, at least in my case. This is not an issue with just a few boards.
The Supergun is solid, I have tested over 200 boards and my only issues have been the sound missing on some bootlegs and Chequered Flag. This is not a big deal, as I have the same issue with my Sigma Raijin and these boards.