Quoted from CactusJack:It's that exposed "line cord" that has me concerned. It may have been there to power the 12VAC transformer mentioned by Inkochnito (now apparently missing).
Your board, featuring the video sound rom, probably worked to some degree and more than likely made sounds like Defender.
I would check across those two exposed line cord wires (with the green one in the middle and see if you have 120AC or maybe 12VAC center tapped there.
Sound Rom 1 is associated with Defender (and a few other WMS Pins and Video Games).
BTW. Those boards do NOT have to run on 12VAC (from a Defender wiring diagram)
defender_2.pdf
In WMS video games, they had +12VDC, -12VDC (unregulated) and +5VDC (regulated) inputs on plug 10J1 in place of using 12VAC.