Help, my trimpots don't adjust!

[ranchak]

I just got done building the Eighteen from Runoffgroove. I built my own board, have everything assembled and my trimpots will not adjust the voltage. I was careful when I soldered them in. I can't believe that I got three bad ones or that I ruined three of them. I don't have any others to replace them with. What do I do now?

[burnt fingers]

Componant failure is always the last answer.  Especially if you have three that arn't working.  Double check your wiring.  They have got to be in there wrong or there is somthing crosswired somewhere.

Maybe remove one and test it with your meter.  It will allow you to confirm the trimmer works and inspect the installation.  If that gets one fixed, the other two should be cake.

Scott

[sfr]

I had this problem once.  Effected signal wasn't making it out, audio probe showed it died just past one transistor.  Problem turned out to be a bias pot - Turned out I had tiny tiny solder trace shorting the trace to the wiper to the trace connecting one of the outside lugs.  So no matter how much I turned the thing, it still worked out as the pot being basically all the way clockwise.  Visual inspection was useless as the short was almost impossible to see w/o knowing where to look (and it wasn't right next to the trimpot) but it was easily discovered checking for continuity where there should be none.

[JimRayden]

To me it also looks like a potential tranny pinout prob. Spectate the datasheet once more and see if you have the tranny the right way around.

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Jimbo

[ranchak]

O.K. Removed one trim pot, it goes from 0 - 100K. Re-install in circuit, same problem - no adjustment. I check the circuit with trim pot removed. Voltage at the source, none at the transistor. Now there are three trim pots all doing the exact same thing. I could see where maybe sloppy soldering on one or two trim pots, but three? I built this project on a perfboard and had the same exact problem. I thought I made a mistake so I made a PCB, but again the same problem. I think I may have found the problem, but I'm new to this electronics stuff. I hooked a battery up to the trim pot that was removed from the circuit. The voltage doesn't adjust. Is 100K not big enough to work? Pablo De Luca if you're out there please help!

[petemoore]

  You can probably measure those trimpots resistances while in the board...?
  If it measures properly out of circuit, and three are not functioning in the circuit, I'd check for continuity across the pot with the dial in the middle just for kicks, assuming it's unlikely 3 pots are failing.