Pinrepair:
Line-Out.
The pre-DCS A-12738 has "line out", through connector J509. This is a tap into the mixed analog signal (from all three sound generating devices) before it going to the volume control and final output amplifier circuits. Connector J509 pin 1 is the Analog ground, and J509 pin 3 is the Analog sound out.
Unfortunately a bit more needs to be done then just tapping into connector J509 to get a usable "line out". On pre-DCS games on the component side of the sound board, lift resistor R102 on the side which connects to pin 3 of J509. On the back of the sound board, connect a jumper wire between the negative side of capacitor C21 and the plated-thru hole left of resistor R102 (which connects to pin 1 of J509). This will give a functional line-out at J509 with the pins indicated above. The line-out you get from this modification is a fixed level and does not get changed by the volume control.
To get a line-out on a WPC DCS game (pre-WPC95), add a two pin .156" molex header to the sound board connector J6 (the left pin is audio and right pin is ground). On WPC-95, just add a two pin header to sound board connector J509 (left pin is ground and right pin is audio). Note the line-out on DCS and WPC95 sound boards is directly controlled by the volume control buttons inside the coin door.