Open the pedal, take out the Color slider switch, open it carefully (pry open the little tabs holding the switch together…carefully don’t break them), try to catch all the bits that fall out on your lap and all over the floor, curse loudly, find the bits that fell on the floor and clean them with contact cleaner — there should be a couple of little brass things that look a bit like staples — re-tension those (bend them a bit) and put it back together again and back into the pedal. See if that helps. Failing that, radio shack sells a replacement switch that will do the job for a couple of bucks.

I have a 76 small stone and mine did the same thing. As was suggested, I went to radio shack and purchased a new switch and it works fine. So it’s probably the switch. Good Luck!

I might have a switch for you. I have a 1977 Doctor Q that I’ve been tinkering with (the decay is warbly) — I haven’t yet tried the switch, but if that’s the problem, I will replace it and you can have the original. A year or so ago, I got some pretty helpful answers about a 1981 Mini-Chorus (not Full Chorus) somewhere in these forums, so I’m glad to have a chance to help someone else out.