Holy shit. I gave my buddy a JNX JAMMA to MVS adapter for his birthday, and it's worked fine on some of my boards. However, he bought a Pandora's Box 4S+ multi-board, and when he put it in, the screen just started flashing like crazy and it made popping sounds. I went over to check it out, and all I could tell was that the 5V rail was all over the place. So, tonight, I brought over a brand new switching power supply, wired it up, and bam, we have picture, but no sound. Long story short, after reseating it a ton and really clamping the edge connector on for, like, 40 minutes, I finally got that bitch running!
We played a game with a misspelled title that he'd researched, which turned out to just be Wolf Fang, which I've played to death on Saturn. Still, I didn't want to spoil the fun for him feeling like he discovered something new, so we played through it.