Volume pot trouble shooting - never had this one before.

[Skruffyhound]

Hello! I haven't posted here in a very long time
I have a friends' pedal on the bench with a volume pot that works fine from about 6/10 to 10/10 but does nothing from 0/10 to 5/10. When I say nothing, I mean that it's passing signal, moderately loud, but won't get any quieter as I turn anti-clockwise down to zero.
In circuit the pot measures 108K from pin 1 to pin 3 and as I rotate it measuring on pins 1 and 2 it goes from zero steadily up to 108K.
It happens to be a Black Russian Big Muff V8 (from 2004 I think) and I've just spent the evening tracing all the wiring through the switch etc.etc. everything seems to be how it should be and original.
It would make sense if there was no volume up to 6/10 and then rapid increase, or something like that, but why won't it go to zero. Tomorrow I'll have to check all the earth connections because, well, surely it's something to do with that... The volume pot is totally standard- Earth on 1 Output on wiper Effect return on 3.
Anyone else experienced this?

[PRR]

Measure Ohms from wiper to output jack ground/shell as you turn knob.

Bad solder joint, cracked pot wafer, c0ckroach poop inside pot.........

[Mark Hammer]

As I all-too-frequently remind folks, much of the dirt in a pot is actually created within the pot.  Wipers - especially well used ones - can scrape material off the resistive strip.  This is where I often recommend that people gently pry the tabs up that are holding on the back of the pot, remove it and clean the resistive strip with suitable materials.  You'll be unsettled by the dirt you see during the removing.

This is also where I recommend that folks get hold of something called Stabilant 22.  It is not a contact cleaner, but is a contact enhancer, and behaves a bit like a liquid solder joint.  Bear in mind that many contact cleaners remove oxidation from the wiper.  If that was the source of the problem, one would not expect to see good continuity above the 2:00 position but none below.  If all that pot rotation has worn away resistive material on the strip - and I find it is most often worn away from the first half of rotation since people usually start volume controls out low and then turn them up - Stabilant will form a conductive layer that maintains the continuity.  It never dries out, and remains viscous for the life of the thing you've applied it to.  Unfortunately, because it doesn't dry out, you can't build up layers with multiple coatings.  So there are limits to what it can revive.  It's also pretty pricey, such that it may be cheaper to get a new pot than buy some of the stuff.  Plus, it may be the case that a good cleaning of the resistive strip will restore continuity.  Finally, while you have the back of the pot off, you can give the rivets that hold the solder lugs on a little "pinch" to tighten them.  Not too tight because that can damage things.  Once you've confirmed the pot is working properly again, you can put the back on again.  Keep in mind those tabs are not meant to be bent back and forth too much, so be gentle with the pliers.

[MikeH]

Just say this yesterday on the volume control of an electric bass. I would suspect the grounded lug is internally disconnected, or the joint is bad. The volume will be affected at first because of the addition of resistance from the pot as you turn it, but never goes to zero because the signal is not being shunted to ground.