Broken Volume Pot

[onelivewire]

So I just picked up a PEC 100K Volume Potentiometer recommended here on the forums from Digikey. Went and installed everything, and I'm not getting any resistance readings on the top left lugs of the pot , and everything after that in that ground line (headphone jack, terminals 12, 14, 20 - all resoldered, too). I get fine readings on the bottom left lug and the RCA jacks. I did notice that even when connecting the multimeter to the casing of the PEC pot, I could get a reading for the bottom left lug, but not the top left lug. This seems odd to me - do I have an issue with my pot, rather than with my soldering? Or am I to blame?

 

[mcandmar]

Sounds like a bad pot, i have seem fail and go totally open circuit before.  With no source connected to the amp i would test between the three pins on each row of the pot and see what figures you get, if they dont make sense remove it from the amp and repeat to verify it is the pot at fault and not a wiring issue.

 

[onelivewire]

Alright, so I went ahead and reinstalled the old volume pot, but I'm having the same issue, and was shocked trying to plug in headphones.
I've been following the ground resistance path guide, and no matter how many times I resolder it, I cannot get a reading on the top left lug - I don't get readings on the bottom two lugs of the headphone jack, terminal 12, terminal 14, or terminal 20. However, if I attach a lead to the top left lug of the volume pot, I find that there is clear path from there to terminal 20, as I will get a reading for this. Is there a reason why the top left lugs shouldn't be grounding? Any insight would be much appreciated!

 

[onelivewire]

Oh, I should note that the LEDs stopped turning on for me as well.

Edit: I was replacing the washer on one of the speedballs, as the screw had come loose, and after fixing it... well I unexplainably am getting readings from the top left lug of the volume pot now, but the LEDs are still off.

Edit 2: Aaaaand, the readings are gone again. I cannot ascertain as to why

 

[mcandmar]

Ok something is obviously very wrong in that case, i suspect something has been shorted out, possibly the washer on the speedball board.  Until you find the source of the issue do not plug the amp in and attempt to power up. PB will have a better idea of where to start troubleshooting but in the meantime i would start by going over the resistance checks in the manual and post back anything that seems out of spec..

 

[onelivewire]

Ok, after a resistance check, I'm not getting readings at:
Terminal 6, 7, 9, 10, 12-14, 20, B3, B6, and center pins

 

[Paul Birkeland]

Ok, after a resistance check, I'm not getting readings at:
Terminal 6, 7, 9, 10, 12-14, 20, B3, B6, and center pins

Terminals 6 and 10 go to ground through the 2.49K resistors on the headphone jack.  It's literally a solid piece of wire that connects each of those terminals to its resistor.

Having high resistance at 7/9 with the Speedball is good.  Having a "0" at either of those is a big problem.  (Same goes for B3/B6)

 

[onelivewire]

The resistances I'm getting after a resolder are very high. My top left lug is reading 30 Mohm, and slowly dropping. This follows to 6 and 10. B3 and B6, as well as 7 and 9 gave Overload readings, but I believe they are still good joints, as moving the negative lead to the left lug gave me values of about -2 Mohms in B3, B6, 7 and 9. These were approaching zero slowly as well. With the negative lead on the top left lug, 6 and 10 both measured as solid connections at 0 ohms.

I should note that I do have a pair of Dayton 100uF 250V output caps installed, but they worked phenomenally for a week while I waited for the PEC pot to come in.

 

[onelivewire]

Any recommendations would be super-appreciated! I really don't know what I could change anything to make the top left lug ground properly. Should I test the LEDs to see if I shorted something speedball with that stray washer - or would the fuse likely have blown first? Once again, any help is much appreciated!

The Best,
one

 

[Paul Birkeland]

Any recommendations would be super-appreciated! I really don't know what I could change anything to make the top left lug ground properly. Should I test the LEDs to see if I shorted something speedball with that stray washer - or would the fuse likely have blown first? Once again, any help is much appreciated!

The Best,
one

Fix the pot first, the Crack may not work properly without the pot functioning as it should.

 

[kscwuzhere]

Any recommendations would be super-appreciated! I really don't know what I could change anything to make the top left lug ground properly. Should I test the LEDs to see if I shorted something speedball with that stray washer - or would the fuse likely have blown first? Once again, any help is much appreciated!

The Best,
one

Fix the pot first, the Crack may not work properly without the pot functioning as it should.

Isn't his stock pot working?

 

[onelivewire]

What readings should I get directly off of the volume pot lugs if it's on the chassis? I have the stock volume pot in right now, which I can unsolder and check to make sure it's functioning properly. Thanks for the help!