Hey, guys. Does anybody have any experience getting a Nintendo Vs. light gun to work on a Unisystem cab?

I've got a properly modded PCB with an original Gumshoe chipset installed. The gun is properly installed in the cabinet. When I start the game, it recognizes trigger pulls, but it's not functional--ie no shots register when I shoot at something.

My friend had the same problem with this on his Unisystem, but when he installed it on a red tent it worked fine.

Adjusting the brightness hasn't yielded any results. I know the gun works in a Unisystem cab because I've seen VS. Hogan's Alley running on a Unisystem in the wild. Anybody have any advice for us?

Thanks in advance!