What did I do wrong? Bizarre Volume Knob Behavior

yeatzee

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Long story short I've got a Fender CS Tele Thinline, I'm the second owner. When I got the guitar the volume knob when rolled back would get crackly at times, and when rolled way down or all the way off and was bumped it would suddenly get full volume. Bizarre. I tried cleaning with deoxit on several different occasions and nothing it just got seemingly worse and worse so I bought new mojo pots to replace it with. Just finished wiring it up and the volume works as you'd expect from say 10 - 1.5, then when it is to the point of almost being inaudible if I keep turning it suddenly it jumps to full volume. For the rest of the pots range it has left (say 1 to 0) it stays at full volume but if I turn the knob all the way to where it hits the rotation limit it's intermittent in and out. There's also an additional hum when the knob is past 1 and jumps back to full volume which isn't present when it's on 10.

I believe I hooked up the pot the same way the factory one was so I'm perplexed. If it didn't work at all ok that's fine I messed up the soldering and I can redo that but here I have no idea what to do.

Below is a recording starting with the guitar at full volume and slowly turning down. You'll hear it be almost silent then jump to full volume and I went back and forth a couple times. Then you'll hear the crackle when I reach the limit of the pots rotation. After that I turn on a RAT and show how at full volume it's regular noise and then when I roll back and hit the point where it goes back to full volume after being almost silent there's a loud hum that's not present on 10.

https://soundcloud.com/tanner-yates-872622389%2Ftele-volume-knob-test
Any help I can get would be much appreciated! This was the stock wiring:



The only change I made was cutting the wire seen going above the pot in half since fender for some reason used one single wire to go from the tone pot through the volume pot to the switch meaning I couldn't remove the pot without snipping the wire or desoldering it from the tone pot and removing it's cloth shield on the side inbetween the tone and volume pots.
 

ARandall

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Typically I'd say that was grounding. But your skill/joint quality is not indicating any poor work involved.

You might just have a faulty pot where the wiper is travelling past the end of the track.....other than that I've got no logical theories.
 

cooljuk

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There's a few things that this could be.

Here's a starting place - looks like you are trusting that foil shielding on the plastic pickguard to provide grounding to the pot casing, which can be unreliable.

I know Fender does this, and has done this, but if you're having trouble you could try a direct soldered ground buss.
 

cooljuk

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Also, make sure the lugs of your two pots are not nearly touching each other, or the cap legs, or the internal walls of the cavity, etc. when installed, and that the pots are installed firmly, but not to the point of damage, with lock washers.
 

cooljuk

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You seem to have a lot of capacitors in there. I think I see at least three?

Here's a schematic. Yours is different. Is it stock?

 

yeatzee

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Typically I'd say that was grounding. But your skill/joint quality is not indicating any poor work involved.

You might just have a faulty pot where the wiper is travelling past the end of the track.....other than that I've got no logical theories.
That's the stock wiring, I took a photo before installing the new pot to make sure I had everything soldered to the same place. Mine's not as pretty, but it functions perfectly normal for 95% of the pots travel. Totally fine. It's the last 5% that's behaving weird. That'd be a bummer if it's a faulty pot, I still think I did something wrong just not sure what!


There's a few things that this could be.

Here's a starting place - looks like you are trusting that foil shielding on the plastic pickguard to provide grounding to the pot casing, which can be unreliable.

I know Fender does this, and has done this, but if you're having trouble you could try a direct soldered ground buss.
Would ground be causing the pot to not function normally on its last 5% of travel? That's mostly what I'm concerned with, the hum also only occurs during that 5% travel.

Also, make sure the lugs of your two pots are not nearly touching each other, or the cap legs, or the internal walls of the cavity, etc. when installed, and that the pots are installed firmly, but not to the point of damage, with lock washers.
When I open it up again tomorrow I'll confirm they aren't touching, I know it's close but i'm almost positive they aren't. Would that cause the pot to not work right on its last 5% of travel? That's what I don't understand, it works perfectly except that last bit.

You seem to have a lot of capacitors in there. I think I see at least three?

Here's a schematic. Yours is different. Is it stock?

Yeah it's three. That's the stock wiring from Fender CS. I believe they call it greese bucket wiring or something like that? No clue what it does, but I have no complaints with how the guitar performed stock, apart from the dang intermittent pot!
 

yeatzee

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Would burning up the pot potentially cause the issue I'm describing? I've heard that can happen, I'd be very surprised if I did because I was not on it long, much less than I've done on my LP in the past. I've heard burning up a pot would result in it not work correctly, but I haven't heard of it malfunctioning in one specific spot of its travel. Maybe some solder could have gotten into the pot on the track where that last bit of it's rotation is causing issues? Hmmm
 

Rocco Crocco

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Pots can get burnt on one specific spot... where the wiper is sitting along the rotation when too much heat is applied. I think your pot is bad... may have been that way when you got it or it could have been burnt when you installed.

I always forget to do this, but when soldering a pot, it should be turned all the way down to zero.
 
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jonesy

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It's not a grounding issue. Sounds like there is a short somewhere that is bypassing the volume pot and allowing the signal to go to full strength. Pot could be shorted as Rocco Crocco suggested.
 

jonesy

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NOTE: Why not use a multimeter to diagnose the problem??? :facepalm:

You could determine in 2-3 minutes where the leak is and if the pot is bad (or good) by using a meter. It takes a lot of the guess work out of these type of problems. I see these kind of threads quite often here at MLP where theory and speculation go on and on and the problem is still not solved.

If you plan on working on your own guitar wiring then invest $20 in a multimeter and learn how to use it. When used properly the meter does not lie and is one of the best ways to find problems in a circuit. Saves a lot of time and headaches.

Best regards,

Jonesy
 

yeatzee

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NOTE: Why not use a multimeter to diagnose the problem??? :facepalm:

You could determine in 2-3 minutes where the leak is and if the pot is bad (or good) by using a meter. It takes a lot of the guess work out of these type of problems. I see these kind of threads quite often here at MLP where theory and speculation go on and on and the problem is still not solved.

If you plan on working on your own guitar wiring then invest $20 in a multimeter and learn how to use it. When used properly the meter does not lie and is one of the best ways to find problems in a circuit. Saves a lot of time and headaches.

Best regards,

Jonesy
I have a multimeter, give me instructions on what to do and what I'm supposed to look for and I'd be happy to check and report back.
 

cooljuk

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I like the Greasebucket circuit, myself. The way I'm familiar with Fender using it is two caps and a resistor, though. ...but I can't find a schematic for the CS version of your guitar, so just focus on your pot.

You COULD fry a pot in such a way as you describe but it takes lots of heat and time and your soldering looks quite nice so I don't suspect that.

A pot can fail mechanically in the way you are describing, too. Say you had a heck of a time pushing the knob onto the pot shaft - the shaft attempts to push through the back of the pot and loosens the tabs on the casing. Then, it doesn't rotate properly inside, making and breaking connection here and there. That "push through strength" is actually a stated spec on CTS pots, when ordering them from the manufacturer. They know it's a problem and charge more to address it.

A ground can indeed be the cause of such a failure, as well. Especially if you are relying on the foil shield for grounding. Consider this - you rotate the pot to its physical limit, the pressure of your hand causes the pot to rotate or tilt in the pickguard (just ever so slightly) and the mechanical connection between the lock washer, the bushing, and the foil sheet opens a little. You're no longer sending signal to ground and the guitar "un-mutes" to full volume as a result. You can add some alligator clips as jumpers to the backs of all the pots and to the output jack or string ground, if you want to test this in a temporary way (though it might be hard to close up the guitar with a bunch of jumpers in there).
 

jonesy

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I have a multimeter, give me instructions on what to do and what I'm supposed to look for and I'd be happy to check and report back.
Set your meter to ohms, select range above 500K, 1M, 2M or whatever your meter has.

You are going to want to test the pot and see if it is working properly. This video will help you understand how a pot works and how you connect the meter to the lugs to test it.

 

Antigua

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Long story short I've got a Fender CS Tele Thinline, I'm the second owner. When I got the guitar the volume knob when rolled back would get crackly at times, and when rolled way down or all the way off and was bumped it would suddenly get full volume. Bizarre. I tried cleaning with deoxit on several different occasions and nothing it just got seemingly worse and worse so I bought new mojo pots to replace it with. Just finished wiring it up and the volume works as you'd expect from say 10 - 1.5, then when it is to the point of almost being inaudible if I keep turning it suddenly it jumps to full volume. For the rest of the pots range it has left (say 1 to 0) it stays at full volume but if I turn the knob all the way to where it hits the rotation limit it's intermittent in and out. There's also an additional hum when the knob is past 1 and jumps back to full volume which isn't present when it's on 10.
It's definitely any issue with the wiper losing contact with the resistive strip of the pot. If not for that treble bleed cap, there would be no sound at all. The volume pot is wired as a voltage divider, as you turn it down, it puts more resistance between the hot lead (center lug) and the pickup(s), and less resistance to ground. But once the wiper loses contact with the resistive strip, there's no connection between the hot lead and ground, and the hot lead is connected to the pickup(s) via that treble bleed cap alone, which apparently produces something close to full volume.

The theory that the wiper burned the surface of the pot during soldering seems the most plausible to me. The pot is too new to have oxidized over. You might not have held the heat on long, but soldering guns with wide tips, for example, can get the parts really hot really fast.
 


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