Gerkin clip trimpot issue

[qak]

I'm having a weird problem with the Gerkin fuzz and wondered if it's a problem with the PCB or just me.

Got everything working (or so I thought) and boxed it up, but didn't test the trimpots. Duh.

Then I noticed, that with the CLIP trimpot all the way to the si diode side, it goes silent. So I removed the trimpot, D3 & D4 and changed C8 in case the cap was bad. So I noticed that the space where leg 1 of the trimpot goes is grounded (as well as where the diodes are connected), but otherwise all seems good and continuity checks out ok.

I tried to figure this out for a few hours, but couldn't figure out what is grounding the connection between the diodes and trimpot leg 1. I think there might be a short in the PCB itself.

In the meantime, I lifted leg 1 of the trimpot and soldered the diodes directly from the trimpot to C8 and now the CLIP control works as it should.

 

[Chuck D. Bones]

I looked at the PCB photo on the PedalPCB website. It appears that the square pads under the two trimpots might have insufficient clearance around them. If so, then pin 1 of one or both trimpots would be shorting to the ground plane on the top layer. You could try measuring the resistance between the square pad and ground, I'll bet they are indeed shorted. You'd have to remove the trimpot to see or fix it. The fix you implemented will work fine. Alternatively, you could remove the trimpot and scrape the corners off of the square pad until the short is gone. Does the Voice trimpot work correctly?

 

[Robert]

Sorry for not seeing this thread sooner!

Chuck is absolutely correct. This was an error on the first run of Gerkin boards, but they have since been modified / corrected.

I can send you a replacement if you'd like, or a credit towards another board since you've already got this one working.

 

[qak]

Thanks for the info you both! I guess the voice is working as it should (don't have anything to compare it to now), although it does change quite dramatically after the first 15% of the turn.
I got the board from Musikding and built it for someone else. I don't think I need another board, but a credit for another PCB would be nice! Either here or Musikding is fine.

 

[Chuck D. Bones]

That's normal for the Voice trimmer. It might as well be a switch because all of the action takes place at the two ends of rotation and there is a big dead spot in the middle.