When the external volume control is bypassed, like it is in flash, the volume pot is extremely touchy, but you should be able to get a reasonable volume level out of it. I think its wired backwards or the schematic is wrong, CCW for louder, don't think I ever swapped that back around on the replacement sound board.

If you can't get a good volume out of it and don't want to solder on the circuit board, add a pot back to the four pin plug with the red wire jumper. If you look at the wiring diagram from a later game with the coin door volume pot you should be able to figure out how to wire it up. Just make a little pot hanging off that plug with a short run of wire.

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