Hey Rob....I had the same problem with my footswitch on my JCM900 a couple of years ago. Well, not exactly the same problem, here is what mine did. My footswitch has a channel and a reverb switch on it...It got to where I'd push the channel button, and nothing would happen. Then I would push the reverb button and it would change the channels. I never could get any reverb with the footswitch plugged into the amp. Anyway, I took it apart, and like you, couldnt see anything wrong, so I took it to a tech and found out the cable going from the footswitch to the amp had a broken wire in it. They replaced the cable, about $35 if I remember right, and it's worked fine ever since.