Treating a noisy & intermittent potentiometer

[Neil Purling]

The 1M volume pot in my Franken Pye is noisy and the volume won't entirely reduce to zero, (as it should). The problem is intermittent & very annoying.

Is it treatable?
I can't see any gap where I might squirt anything in around the terminals.
Would I do any damage if I got the case off and dosed it with a contact cleaner such as Servisol 10 or even DeoxIt?

The only 1M pot I have to hand is a small switch pot off a Pye Piper, the alternative being a modern one with a plastic shaft.
I'd like to try and cure the original if possible.

[Sideband]

If you can take the back off by bending the tabs up then you can put a drop of Servisol on the track and wiper contact. Some people liked to pack the inside of the pot with petroleum jelly. I've never done this but apparently it used to work well.



Rich.

[jay_oldstuff]

If it looks too tricky to get the pot apart a trick i've used many times is to very carefully drill a small hole in the back of the pot and squirt some servisol in, has worked for me a number of times.

Jay

[paulsherwin]

You can almost always dismantle pots by bending back some lugs somewhere, though it can be fiddly.

This is one of the few cases where WD40 is a good solution. It dissolves crud better than Servisol and the mineral oil component seems to help with subsequent operation.

Paul

[Neil Purling]

I thought about drilling a tiny hole in the case, but then wondered what problems the drill swarf will cause. The thinnest drill I have got is 1.5mm.

[electrogram]

I have often drilled holes in pots, I usually drill into the side rather than the back, if you do this make sure you have turned the wiper so you are least likely to hit it with the drill. I use a bit just large enough so that the squirty tube will go in.

[Leon Crampin]

If you need to drill, put plenty of grease around the tip of the drill bit. Most of the swarf will stick to the grease rather than falling into the can.

Leon.

[Biggles]

I read somewhere that some problems with noisy pots can be caused by poor electrical continuity between the shaft and the bush that the shaft fits into but I've never proved this one way or another. I suppose you could try squirting some cleaner down the bushing where the shaft enters to see if there's an improvement.

Biggles.

[GMB]

It's always worth checking capacitors near noisy pots as current flowing through them seems to make them much more noisy than they otherwise would be.

If the volume won't go to zero then I wonder if you have a problem with the track end connection.

[Neil Purling]

Yeah, if the track's fractured the pot is knackered.

[Tractorfan]

Hi,
WhenI was in the trade my gaffer used to try 3in1 bike oil through a drilled hole. I remember us doing it to an ancient 12" Philips telly and it worked that time.
Cheers de Pete

[jay_oldstuff]

Not nesseseraly i have successfuly repaired brakes in pot traks useing conductive paint of the kind baught for repairing heated rear screens on cars, as for drilling pots i do it on the side of the pot useing about a 2mm drill bit use a verable speed drill and go very slowly removing the swarf reguarly.

Jay

[Neil Purling]

I will have a bash at drilling the pot cover first, with a hand-drill. I'll squirt in some WD40.
If this has no effect then i'll just change the pot. FrankenPye is a mixture of 3rd party components now. I assume the material is non-conductive & therefore safer, yet I still see the presence of a modern plastic pot shaft as offensive.

[AlanBeckett]

Neil,
I find a very gentle approach with a Dremmel the best bet.
Alan

[Mike Phelan]

Originally Posted by Biggles

I read somewhere that some problems with noisy pots can be caused by poor electrical continuity between the shaft and the bush that the shaft fits into but I've never proved this one way or another. I suppose you could try squirting some cleaner down the bushing where the shaft enters to see if there's an improvement.

Biggles.

If that's so, it means that the wiper is not making good contact with the central ring, which tends to tarnish. The only way to solve that is by dismantling and polishing the above.

The problem with squirting cleaner into the bush is that the bush should be greased; washing it off loses the smooth operation.

[PaulR]

I have never had much lasting success with using switch cleaner. It sounds ok for a while but then reverts to being crackly.

Taking the case apart is usually just a matter of slowly bending the tabs back. If you bend them quickly they tend to break more easily. The greater problem is releasing the circlip which holds the shaft and wiper onto the body. Perseverence usually works here but have an elastoplast ready for when the screwdriver or whatever you are using slips!

I usually try to get them completely dismantled so that I can clean the wiper thoroughly using silver polish. It helps is you re-tension the wiper towards the track. I clean the track with IPA.

Several people have said that putting Waxoyl in the case works well but I have never tried it.

My son has a Rogers amp on which the volume pots were very noisy. He actually destroyed the tweeter in a speaker because of it. I replaced them with a new pot from CPC but within a year or so that was going crackly so I dismantled the originals and cleaned them as above and they have now worked silently for over 18 months.


Paul

[bob_rich]

Hi

I have had a couple of examples of noisy pots caused by the radio directly connecting the pot wiper to the grid ( no blocking capacitor). This results in the grid bias voltage, (from the cathode resistor) being applied to the grid via the pot wiper. I added a capacitor between the wiper and the valve grid and then a 1 meg pull down resistor to re apply the grid bias. Problem completely solved and did not have to change the pot.

Hope this helps

Bob

[GMB]

Yes, that's another example where it's current flowing through the pot, even tiny amount, that massively increases pot noise.

Another example I have is my FT101 volume pot which crackles like hell for about 5 seconds after switch on. I'm guessing this is while the coupling capacitor is charging up through it. After that it's absolutely perfect.

A new pot I used for my multimeter ohms range voltage setup became incredibly noisy after only a few years. Again, it carries current.

[Fredddy]

hi, I've gone off 'Servisol' (I use Oszillin here in Luxembourg), I now use compressed air - it seems to give a longer lasting clean up of the dust, or perhaps it just blows it into a quiet corner somewhere...

Ray

[Lucien Nunes]

The De-Oxit range includes a product called 'Faderlube'. I've used it with apparently good results, although I can't readily compare the results to any other contact-cleaner / lubricant. It is specifically formulated (they claim) for compatibility with both carbon and plastic pot tracks.

But if you have a break in the track fix that first, otherwise the conductive paint will not bond well once the lubricant soaks in.

Lucien