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Tech: knob control problem ?

GUEST,Dereck Crapton 29 Oct 08 - 11:19 PM
GUEST,Dereck Crapton 29 Oct 08 - 11:29 PM
Peace 30 Oct 08 - 01:25 AM
The Fooles Troupe 30 Oct 08 - 01:58 AM
GUEST,Peace 30 Oct 08 - 02:00 AM
The Fooles Troupe 30 Oct 08 - 02:12 AM
The Fooles Troupe 30 Oct 08 - 02:16 AM
Gurney 30 Oct 08 - 02:53 AM
Darowyn 30 Oct 08 - 03:49 AM
GUEST,Shimrod 30 Oct 08 - 05:13 AM
JohnInKansas 30 Oct 08 - 06:52 AM
The Fooles Troupe 30 Oct 08 - 07:57 AM
The Fooles Troupe 30 Oct 08 - 08:01 AM
Darowyn 30 Oct 08 - 11:14 AM
JohnInKansas 30 Oct 08 - 12:45 PM
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Subject: Tech: knob control problem ?
From: GUEST,Dereck Crapton
Date: 29 Oct 08 - 11:19 PM

The knob controlling the bridge humbucker of my Tanglewood Memphis [reasonable quality Gibson 335 copy]
has stopped working.

I can't adjust it down from full treble any more.

So please whats most likely to need fixing or replacing.

the tone pot, or the capacitor, or whatever other components ?

I already know its going to be a right fiddly bugger of a job
trying to work in and under the f hole
with coathanger wire and string!!!

and I've never used a soldering iron in life ever...

thanks


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Subject: RE: Tech: knob control problem ?
From: GUEST,Dereck Crapton
Date: 29 Oct 08 - 11:29 PM

forgot to mention the knob still turns ok, just no longer varies the tone


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Subject: RE: Tech: knob control problem ?
From: Peace
Date: 30 Oct 08 - 01:25 AM

Take a cold shower--BUT, not with the guitar.


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Subject: RE: Tech: knob control problem ?
From: The Fooles Troupe
Date: 30 Oct 08 - 01:58 AM

Take yer hands off yer knob,
Put yer fingers on the strings.
Keep yer beady eyes on the music stand ahead.
We're having fun, standing in the back row,
Strummin' and a buskin' with Fred!

Sorry...
I'll leave now....

:-P


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Subject: RE: Tech: knob control problem ?
From: GUEST,Peace
Date: 30 Oct 08 - 02:00 AM

"I can't adjust it down from full treble any more.

So please whats most likely to need fixing or replacing."


Your ear drums.


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Subject: RE: Tech: knob control problem ?
From: The Fooles Troupe
Date: 30 Oct 08 - 02:12 AM

"So please whats most likely to need fixing or replacing.

the tone pot, or the capacitor, or whatever other components ?"

Depending on the construction material of the capacitor (and I won't give a lengthy discussion here) - capacitors of the type used in that application tend to be robust and have a long life.

More likely is the variable pot (potentiometer). Usually the wiping contact that moves gets dirt under it, or some other problem. A squirt of the correct pot lubricating liquid (NOT WD40! - which is NOT a 'lubricating', but a 'cutting' oil) will usually bring it back. Otherwise a replacement may be called for.

If the sound is still getting thru, then while it may be a failed (dry) solder joint, then it will most likely be confined to the area of the capacitor and pot wiper arm connector.


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Subject: RE: Tech: knob control problem ?
From: The Fooles Troupe
Date: 30 Oct 08 - 02:16 AM

Further.

"can't adjust it down from full treble"

This probably means that full treble cut is being constantly applied thru the capacitor - a guess is that the capacitor is being 'in circuit' all the time and the pot is not 'removing it from circuit'.


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Subject: RE: Tech: knob control problem ?
From: Gurney
Date: 30 Oct 08 - 02:53 AM

Silly, but not unknown... is the knob loose ON the shaft, or turning the shaft, as it should?


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Subject: RE: Tech: knob control problem ?
From: Darowyn
Date: 30 Oct 08 - 03:49 AM

I suspect that Foolestroupe has it backwards. The capacitor filters the high frequencies to earth to cut the treble, with the amount filtered controlled by the tone pot.
I would think that the most likely problem, unless the tone pot was very crackly previously, or you have dropped the guitar onto the control pots, is that the capacitor has become disconnected from the pot, or more likely, from the earth tag.
You get full treble all the time because the capacitor is never in the circuit.
Cheers
Dave


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Subject: RE: Tech: knob control problem ?
From: GUEST,Shimrod
Date: 30 Oct 08 - 05:13 AM

I was hoping for some good 'knob gags'! But all I got was some boring techy stuff about guitars!


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Subject: RE: Tech: knob control problem ?
From: JohnInKansas
Date: 30 Oct 08 - 06:52 AM

If the info at Guitar Wiring is what you've got, the pot and the capacitor are about the only components associated with tone control that might be likely to fail. You can also refer to Wiring Information for Humbucker Pickups which gets you a .pdf that might be easier to save for later.

With some potentiometer constructions, it's possible for the "wiper" to be bent so that it doesn't contact the resistance element it's supposed to wipe against. If this is the problem, you'd probably need to get the pot out of the guitar to do any "fixing" on it, and pots are usually cheap enough that if you've gone to the trouble of getting it out you'd want to replace it rather than messing with trying to make "adjustments."

As Foolestroupe indicated, cleaning the pot "wiper" with an appropriate lubricant or "contact cleaner" solution may work - if the wiper is in place and isn't making good contact, and if the pot is a sufficiently "open" type that you can get the solution into it.

Although it's rare, capacitors can fail. If this is the problem then replacement of the capacitor is the only thing that will help.

A "cold joint" in the wire connections could have lost it's electrical connection, in which case re-soldering may be all that's needed. Sometimes just "wiggling" the wires will show which one isn't carrying the signal, but it's possible to have a fairly sturdy "mechanical joint" without a good electrical one. A volt-ohm meter judiciously used is usually the best tool for sorting out whether this is part of the problem.

As also noted, sometimes a knob loses "traction" on the pot shaft, so that turning the knob doesn't turn the shaft. You can pull the knob off and try turning the shaft directly with your fingers to verify that turning the shaft doesn't change the tone. The knob may have a "set screw" that can be tightened (and/or replaced); but if it's a "friction fit" knob you probably would need to replace it.

Having a crossover switch set wrong might make everything sound a little like it's at max treble(?) even if the tone control is working - on some guitars.

John


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Subject: RE: Tech: knob control problem ?
From: The Fooles Troupe
Date: 30 Oct 08 - 07:57 AM

"You can pull the knob off"....

not going there - been there, done that before....


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Subject: RE: Tech: knob control problem ?
From: The Fooles Troupe
Date: 30 Oct 08 - 08:01 AM

My comment about the capacitor was not completely wrong, if you look at the Gibson wiring diagram in the first link John gave... :-P


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Subject: RE: Tech: knob control problem ?
From: Darowyn
Date: 30 Oct 08 - 11:14 AM

Calacitors pass more signal as frequency increases. Both wiring diagrams on the link show the capacitor between the signal path and earth, whether the tone pot comes before or after the pot. The more of the signal that goes to the capacitor, the more the high frequency is cut.
If it's stuck on full treble, the capacitor is not in the circuit.
In practice, guitar makers often use the body of the pot as a central earthing point, and they connect a number of earth (ground) wires there, so the capacitor may be directly connected from EITHER the end terminal of the pot and the other end to the metal part of the pot body, or from the central, wiper terminal to the body. That is the main difference in tone wiring between the Gibson and Fender version.
If the fixing nut is loose and the whole pot has been moving about, the wire can break.
Cheers
Dave


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Subject: RE: Tech: knob control problem ?
From: JohnInKansas
Date: 30 Oct 08 - 12:45 PM

Ah yes. There could be a loose nut that's the cause of the problem.

John


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