Quote Originally Posted by celerystalker View Post
Speaker out, though, is pins 10 and L for both, so it should be functional
That's incorrect, 10 and L are ground and hot for mono sound on a JAMMA board. On a MVS system they're both hots for left and right speaker, so if you slap a JAMMA board in you're crossing hot with hot.

Pin 11 is the hot for one speaker mono audio on MVS, but on JAMMA it's a preout audio hotwire that isn't amplified.

The audio wiring and the test button issue are the sole reason people buy MVS-to-JAMMA fingerboards. Single slot MVS boards do not have these issues though, they're JAMMA compliant.