I had a similar problem with my ds-1. my friend gave it to me as a sort of "if you can make this work it's yours kind of thing." it wouldn't turn on, but then when I opened it up to inspect it, everything worked fine. what was happening was that the board was shorting against the bottom of the case. the low cost solution was to coat the panel with electrical tap. the other problem was that the momentary switch wasn't returning to origin. I took that apart before I tried to replace it, the internal spring had slipped off of its seat and kinked, I just bent it back and I haven't had a problem since. If I had to guess what happend to the pedal, he stomped on it a little too hard, broke the switch, and then when it stopped working properly, he just threw it across the room.
I got a vintage ampeg from him dirt cheap($10) in a similar manner. when I got it, it was missing the power tubes, the chasis was bent, all of the shock mounts and a knob were broken, it had a blown fuse, and the rectifier was bad(the tube had white junk on the inside of it, which I didn't think was right). If I had to guess what happend, I'd say that the rectifier went, took the fuse with it, and when it stopped working, he threw it, causing the chasis to fly out of the head, and possibly causing the power tubes to go along with it. after checking the electronics for shorts and bad components, geting a voltage reading off of the power transformer, and in general just looking for other possible failure modes, I concluded that my friend is an idiot, replaced the tubes and fuses, and fired it up. it sounds awesome now, and the prices of old ampegs are on the rise. I made out like a bandit.
Obviously, I don't let this guy near my stuff anymore.