Electro-Harmonix Holy Grail Reverb Repair

I recently bought a non-functioning Electro-Harmonix Holy Grail Reverb. It's chock full of surface mounted components, so I wasn't sure if I could fix it, but having successfully repaired one of these before, I thought I'd give it a go.

Fig. 1. EHX Holy Grail Reverb, original enclosure.

Visual inspection revealed nothing, except a few solder joints that looked sloppier than stock. I plugged it in to verify that it didn't work, and indeed it didn't. Oddly, though, when I turned the knob, I briefly heard a reverb-soaked pop/clank sound, almost like when you jar an amp with the spring unit in it. Thinking something must be loose, I left it on and poked every wire and component that was big enough to poke with no luck.

Fig. 2. Everything looked good on both sides of the board, except for the three solder joints on the upper left of the board, which looked like they had been redone. That turned out to be irrelevant.

I ran out of time, so I left it for a week or so. I plugged it in again and it worked (?!). I moved all the controls, unplugged it and plugged it in again, and it did NOT work. After poking everything again and even wiggling the board while it was on, it occurred to me that the pot might be the culprit. I sprayed the crap out of it with DeOxit, gave it a little squirt of compressed air and turned it back and forth several times.

I plugged it in and it worked. I fiddled with all the knobs and plugs like before and it still works. It must have had some gunk in the pot. It turned out to be less complicated than I expected.