Vintage WAH repair?

I have Cry Baby from the late 70's, circuit photo below, Model# 95-910511. Has been working fine over the decades but gets minimal use.

I let it sit in the closet for a couple years and just pulled it out. It's throwing oscillation and massive amounts of noise when switched on. If I have it all the way back the tone is as expected (dull wah), but advancing the pedal to any forward point at all results in nasty noises. It doesn't have to be moving - just adjusting the pedal forward a smidge gets the noise.

It's not the basic pedal wiring... the sound is fine with the wah section switched off. I unscrewed the circuit board and looked over the bottom side. There are no obvious bad or degraded solder joints (but I didn't reflow anything).

Where should I start checking?

 

This doesn't seem to really be a dirty pot issue... it's a screaming oscillation along with lots of noise. I could see the noise coming from a bad pot but not the oscillation.

BUT, what do I know. I'll experiment a little. If it's the pot, I should be able to simulate values with another pot wired in to test (before investing $20 in a special WAH pot). I'll report back.

 

Good idea, I'll check /bypass the switch into wah mode while I'm in there. It is fine with the the WAH switched out so it's not the jacks.

 

Initial testing indicates the pot is bad. I will swap it tomorrow and see where I get.

 

So the pot swap helped, but I still have issues.

You know that high level hiss you hear with a/any (well working) VOX WAH when the pedal advances to full? Well, I have it but multiplied about 20 times in volume. To the point of becoming almost a staccato buzz. Worse the more pedal you give it, just like the standard hiss, but again, 20x worse. It's like it has it's own gain section. Otherwise the pedal seems to sound normal.

Ideas?

 

Thanks, I was planning on going that way.

It also occurred to me that this seems like a grounding issue. I've done the basic checks on that and it passed. Also, when switched off it passes the signal OK (no bypass on this oldie) so I figured the jacks were OK. But, now I'm suspicious that maybe the ground is marginal and the WAH circuit is magnifying it.

I'll recheck all that and do some reflowing. Can't hurt!

 

Just wanted to follow up on this: Turns out the pot was not the issue. I have swapped the vintage pot back in because vintage.

It all came down to dirty jack contacts and the jacks not grounding to the chassis properly. I spent some time sanding the contact points, which helped but it was still noisy, intermittent, and hissing treble. I figured I needed new jacks, but as a last ditch I pulled them out an sanded the metal contact surface along with the top of the jacks.

That did it! Sounds good, nice and smooth. Need to test it into an amp but it sounded great into muy headphone amp.

I might have gotten away with just loosening and tightening the jack nuts, but I figured that doing it right should set it up for another 40 years of service. I'll likely be dead but someone younger can use it to reproduce 80 year old music only old goats listen to.