Sorry to hear this, Simon. A photo could be helpful. Hold the camera/phone reeeeeel steady. The designer of the Percolator is, even as we write, at his brother’s wedding reception, out-of-state. It will be tomorrow night at the earliest that I can put him in front of a PCB and, hopefully, your photo, and we’ll trouble shoot with you. In the meantime, LEAVING THE AMP SAFELY UNPLUGGED, you could carefully check continuity from each of the switch contacts to ground (the chassis). Note which ones appear to be continuous to ground, with the switch both on and off. This will help us get started.