In general, a Jamma board needs +5V to power on (and operate it) and +12 for sound.
But, some Jamma boards also require -5v for sound, so, if you power a the game up, and the +12V lines are attached, but the -5v lines are not attached, and you don't hear any game sounds; then, your next move should be to turn the game off, attach the -5V lines, turn the board back on, and see if you get any game sounds.