I’m in the process of writing a troubleshooting guide for the VPM-1…but it’s been hard to finish due to the pandemic and me not working at the lab much.
As far as the volume not turning off…check the optocouplers (especially on the LED side) to make sure that one of the heat shrink tubes didn’t pop open, or has an “optical” leak that could let light in. If so seal it with some opaque material…like caulk or even sticky tack (poster putty). I use black hot glue for this.
You can also try to re-setup the microcontroller’s memory registers by running through the stereo set up procedure. To do this jump together the 2 pads of “CAL1” as you plug in the power. Once the power is on you can remove the jumper…i just use my metal tweezers to short the pads together upon power-up. The red LED will start flashing for a couple of minutes as it re-writes the registers. It will flash 256 times, if you care to count. When it is done writing, the green LED will start flashing, letting you know that you can unplug the power and remove the jumper if it’s still on.
As far as it not working anymore, what do you mean? Does the LED turn on? If not, check your DC jack to make sure the wires are still intact. Then check to make sure the voltage regulator is putting out 5V, which powers the microcontroller, which light up the LED.
As always, check for solder shorts with your magnifying glass.
Let me know what you find.
-Brach