70's MXR Phase 90 & Envelope Filter won't work

randy barnes · From: alexandria, MN USA

I recently took these gems out of storage and tried them out but can't get them to work. I'm wondering if anyone knows what I should check in the circuitry to see why they won't work? Appreciate any input on how to get them working again. thnx

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Make sure the battery connections are good, and that there's no corrosion. Any other problem (most likely dried electrolytic caps) will have to be replaced by a technician. Should you decide to go that route, realize that you can probably buy working (used) units for what it might cost to fix your defective ones. Crying or Very sad

It should be made more obvious that many electronic devices cannot be put into long-term storage with any reasonable hope of them working 10 or 20 years down the road.

Stephen Cowell · From: Round Rock, Texas, USA

Make sure you're not using a TRS ('stereo') cord on the input... the battery is turned on by making the connection via the input jack; has to be a 1/4" mono plug to work right.

Make sure that the battery is good/connector is tight... make sure that the jacks are clean inside. Switch the switches/turn the knobs/plug the plugs several times, these things are self-cleaning to a degree. The switch contacts are designed to wipe... if they're not used for decades then oxidation can build up. There's probably no blown components... electrolytic caps can dry out but try everything else first before 'shotgunning' them.
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