Intermittent Nano Big Muff Pi volume drop

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Hey all. I recently bought an "excellent" condition Nano Big Muff Pi off Reverb with an intermittent volume drop making it virtually unusable. My understanding is that fuzz circuits are on the less complex side of pedals, so I thought I might spin it as a learning opportunity.

It's not intermittent in the sense that I jiggle a knob or a cable and it cuts in/out; rather it will work perfectly for awhile then I'll turn it on one day and it drops the volume so low that at first I thought no signal was getting through at all. Once it's like this it stays like this until it just starts working again one day.

Symptoms:

• For days/weeks at a time volume will drop to a whisper, regardless of messing with knobs or changing cables
• It has gone back to normal once for about a month, then regressed; both seemingly randomly
• LED reliably stays on when pedal is engaged
• I can hear that the knobs are affecting volume/tone/sustain as expected by cranking my amp
• Bypassing the pedal works as expected
• No crackling; it's either working or it's not

Things I've tried:

• Swapped all the cables
• Removed all other effects from the signal chain
• Tried battery vs power supply; swapped the battery
• Checked the board for cold solder joints and resoldered suspicious ones
• Repeatedly toggled the switch, swept the pots, and plugged/unplugged cables to see if I could clear contacts

That's about it I guess. I mean it looks basically brand-new. While I don't have a scope, I have a voltmeter, a soldering iron, and several years of experience soldering synth parts; is there something I can check? Anything you would start with? Unfortunately the Nano is mostly surface mount resistors, but everything else looks pretty straight-forward.

EDIT: forgot the "Pi" in the name

[52 Bill]

Welcome to the place.

The store that I work in sells these things and in the past I have noticed a common problem with the bypass/effect switches. Try switching the switch rapidly a few times and see if you can cause the problem to start or stop. If you have a can of DeoxIt, spray a little into the switch and toggle it on and off a few times to work it in. That may fix your problem.

Good luck

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Thanks 52 Bill. I picked some up and it really did make everything move super smooth. Unfortunately while reassembling everything a pot snapped ( https://imgur.com/a/jEj1veB ); I wonder if this was the original trouble maker or if the EHX nanos are built...questionably. Going to order a replacement and see what happens.

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Whelp, I swapped it with a 100k pot I had lying around and I'm still getting the volume drop.

EDIT: And rewired the cable between the switch and the main PCB. Still no change.