Here is a Zeta violin that stopped working. I started taking it apart and noticed that there were a couple of wires that had become unsoldered. The plug into the volume pot was unpluged and the batteries were dead. It uses 3 stacked 3v batteries to make 9 volts.
I stripped the shrink tubing from the ends of the wire so I could sleuth which wires went where. At first the plug with 3 connectors threw me off a little, but then I realized that the white wire was a sheilded wire. It's somewhat clever how they must have stripped the sheilding back, then soldered it. Then the hot is just simply coming out of what seems like a soldered ball. That makes it easier to attach another wire to the soldered ball.
Note: Before I loosened the volume pot, I tightly tied and glued a string to the shaft. Then I could get the volume control out and work on it. Then to replace it I used the string to get the shaft back through the hole in the top.