Cleaning potentiometers

[Dead_Nid]

Hi all! Done a search on the subject in the forum and found almost no info. I thought it would be beneficial for all to gather some opinions and tips on what is the ideal way to clean an old potentiometer. Mostly refering to the ones using carbon but any info on other types is mostly welcome.
Personally, I've heard that it is best to use a Contact Cleaner (degreaser) spray with no grease of any kind. If using one with grease then this grease may make matters worse some time later when it dries out. true? false? other?

 

[Dead_Nid]

And don't forget to mention the actual procedure that you follow. For example is it better to open the pot and clean directly the internals or just throw some spray from any opening and rotate the shaft a few times? such stuff...cheers!

 

[ante1]

Hi Nid,

I wouldn’t recommend cleaning any pots at all but when I have to because it can’t be replaced I have used video drum cleaning spray with some success. I flood them completely and work them hard for a minute or so repeating this a few times. But no promises!  ;D

 

[steven2]

i used to use a can of wd40 the same stuff you use to free up rusty bolts on cars and get rid of mioster in your disy pionts, to clean post with

 

[steven2]

i mean potentiometers just spray some in the little opening and rotate the pots so that all that dirt and stuff is cleaned out  and the pots, if they are a bit stiff should be easyer to rotate then, you can use crc to

 

[ante1]

Hi tnk2k,

You are correct, most of the time it’s a write-off but sometimes it can be dirt and dust. Slider-pots especially are more exposed due to their construction. Not all pots have carbon inside, many have a cermet “track” inside which do not wear out as easy as carbon.

 

[Dead_Nid]

Hi!

I guess when the specs of a pot have changed there is nothing more you can do to save it, right? I am trying to refurbish an old 100K stereo pot. At its fixed center position it gives about 10K difference between channels, measured on its own (not on any circuit). After some cleaning I managed to narrow the difference down to 8K...waste of time. So I guess this is why my left speaker plays at a slightly lower level than the right speaker for about a year now...(The pot is for the Balance control).

Best regards!

 

[ante1]

Hi Nid,

If you are desperate enough you might try reducing the difference by moving one of the tracks slightly. I don’t know the mechanical construction of the type you’ve got but it might be possible and worth a try if there is nothing else wrong with it. Each track is sometimes made on a separate strip of fiberglass or similar and this way they can be moved independently, if filed of in one end.
But you’re maybe not that desperate! ;D

 

[MP1]

Potentiometers are being manufactured very cheaply these days. You used to see a much better quality in potentiometers. Lately, most pots will not have a cover or will have an open frame where it is easy for dirt to get on the resistive material.
Years ago there was no such thing as contact cleaner for potentiometers. As mentioned above in an earlier post, many of us used WD40 or similar. This was not very good because it left a residue and the pot got dirty again at a faster rate. It worked well in an emergency. The new contact cleaner is pretty good stuff since it dries with no residue and evaporates quickly.
I notice a dirty pot most in audio circuits where you get pops and scratches when rotating the knob. Of course, cleaning will not help a damaged pot come back to life.
A 100K pot? That is a pretty standard value. If it is damaged, couldn't you replace that one for very little $$? As long as the value is the same, all you have to be concerned with is the watt rating and number of turns.

MP

 

[Dead_Nid]

Hi! This is a 2-gang pot metal-shaft with a center click fixed position made by ALPS. Type 100KMN. It is used for the balance control between the 2 speakers. So when it is in the center position it should measure 100K for gang-1 and 100K for gang-2. However it measures 88K and 82K respectively. As I told before, my left speaker was playing a bit lower than the right one. Is this 6KOhm difference audible or am I searching in the wrong place?

MP, 100k sure is pretty standard but it is also a matter of dimensions and it is ALPS, rather good quality...I got a plastic pot from Piher from a local store to replace a volume pot and yikes...Raising the volume you could hear the signal swinging from one speaker to the other. Then I measured it gradually and found out that my ears were right. So, I will definitely replace the pot but not until I find a good one and that's not an easy thing to do in my country. That's why I am looking for international stores to order from.

One last thing that just came to my mind. Let's say I don't need the balance control. I want my speakers to play equally everytime. So isn't it reasonable to put two 100K static resistors in place of the pot? (Does it matter if it is a little less or more than 100K?) But the total resistance for each channel should be equal. Common resistors are not that accurate as far as I know. Let's say that you buy 2 resistors of 47K. One might measure 45K and the other 48K...so same shit. Is there some type of resistor that is very accurate?

Thanx!!!best regards!

 

[audioguru2]

Hi Dead,
Usually the balance control on a stereo amp is a single pot. Your amp probably uses one pot to attenuate one channel while the other boosts up to 3dB. In the center position then both channels are attenuated 1.5dB. Do you have a schematic?

 

[MP1]

A 100K pot will not measure 100K in the center position if you are measuring at the wiper. The wiper should give you 50K in the center. However, if the pot is measured in-circuit, you might be measuring across other circuitry as well. Also note that some pots do not have the wiper as the center post. If you are measuring across the pot, out of circuit, then this would seem reasonable for a 100K pot. Most pots are spec'd at a 20% tolerance. Thus, you could have 80K to 120K. If the measurement is linear, you can add resistors to one end or both to fine tune it.
Hope this helps.

MP

 

[Dead_Nid]

Hi! I am measuring out of circuit of course. Now I don't think that this pot has a wiper. In the center position there is a clearing on the carbon layer like there is no carbon there. I don't know if that is called a wiper. So here is a rough drawing to help you get the picture of what I am measuring with my multimeter: (that is on center position)

PINS->

View attachment 38044

 

[audioguru2]

Hi Dead,
The pot has a wiper on its pin 2 and the cleared spot on the track is the tap for pin 3.
When the pot is in its center position then pin 2 should be connected to pin 3.

I don't think the slight 7% difference in resistance between the two sections would be noticeable. It would be less than only 1dB. The room's acoustics and the efficiency of the speakers could be more than that.

 

[Dead_Nid]

audioguru I had done the following thing which I forgot to mention:
I fed some line level inputs (the CD input if it matters) with a constant 1KHz sine tone from a PC pro audio interface. I measured the VAC at both channels right at the input and it was exactly the same amount of a few mVolts. Then I measured VAC at the speaker outputs and found out that there was about 500mV difference with the speaker playing lower getting the fewer volts (so I can't be wrong about my ears). Then measured the outputs of the preamp and there was a respective difference. So I am sure that the unequality comes from the preamp but I am not that good to find out where exaclty without a schematic. But I think that the pots are the first to suspect, right? There are actually four 2-gang pots in the preamp section. They control bass,treble,balance,volume. I took all of them off and measured out of circuit. All show some difference in resistance between gangs but the one for the balance control was the worst.

I am going to post schematic soon.

Sorry for altering the initial subject of this thread but I think we had enough interesting posts on how to clean a pot (at least a carbon pot). I will personally follow the "contact cleaner without any grease" way. Products like the blue Philips degreaser spray. Definitely not going to use the WD40!!! Though it does a great job when my doors' hinges start to squeak

 

[audioguru2]

Hi Dead,
You didn't say exactly how much the levels were different between the channels. Ten percent voltage difference is only about 1dB which isn't noticeable to your logarithmic hearing. Maybe your speakers are out-of-phase, then one that is slightly closer sounds much louder than the other. The bass will be weird too.
When I visit "home entertainment equipment" stores, they always have the speakers wired out-of-phase and the bass cranked-up to try to compensate for the cancellation. I can't stand hearing their amps clipping on the over-driven bass so I quickly fix the wiring, turn down the bass and leave it sounding fine. ;D

I use "contact cleaner" for pots and switches. I think if you use "degreaser" instead then the bearings in the pot will bind and maybe squeak.

I don't use messy WD-40 on door hinges, It attracts dirt then evaporates leaving dirt without lubrication resulting in worse squeaking. I use dry graphite powder as a hinge lubricant. It is good in locks, too.
WD-40 makes a very good flame-thrower. Don't try it indoors! The smoke is pitch black.

 

[ante1]

Hi Audioguru,

I agree, WD40 should not be used for this purpose. We also have another similar “drug” called 5-56 which have the same effect, collecting dirt and making things worse. As I mentioned before I use video drum cleaning spray for this with some success this leaves a non sticky, dry and clean surface.
Yes, it makes a good flame thrower too very effective when you have too many mosquito’s around.  ;D

 

[audioguru2]

I saw a kid with an RC toy car. It had a lighted small can of WD-40 on the back making lots of flame, smoke and noise. I don't think it provided much thrust. :

 

[Dead_Nid]

Hi Dead,
You didn't say exactly how much the levels were different between the channels. Ten percent voltage difference is only about 1dB which isn't noticeable to your logarithmic hearing. Maybe your speakers are out-of-phase, then one that is slightly closer sounds much louder than the other. The bass will be weird too.

Hmmm, if you mean acoustic levels I think about 2db max. My speakers were never out of phase, I mean for several years...hey I am a damned sound engineer.

When I visit "home entertainment equipment" stores, they always have the speakers wired out-of-phase and the bass cranked-up to try to compensate for the cancellation. I can't stand hearing their amps clipping on the over-driven bass so I quickly fix the wiring, turn down the bass and leave it sounding fine. ;D

lol...not everyone is an audio guru.

I use "contact cleaner" for pots and switches. I think if you use "degreaser" instead then the bearings in the pot will bind and maybe squeak.

OK. Here I have in front of me 2 spray cans. Both Philips. One is the blue "DEGREASER CLEANER", the other is the red "CONTACT CLEANER". So, the blue should be good for cleaning e.g. connectors. The red should be good for cleaning pots. Correct?

I don't use messy WD-40 on door hinges, It attracts dirt then evaporates leaving dirt without lubrication resulting in worse squeaking. I use dry graphite powder as a hinge lubricant. It is good in locks, too.
WD-40 makes a very good flame-thrower. Don't try it indoors! The smoke is pitch black.

Yeah actually I am using graphite (in powder or spray can) for hinges too. I only used WD40 in the past. However I didn't know it was that "messy".

I agree, WD40 should not be used for this purpose. We also have another similar “drug” called 5-56 which have the same effect, collecting dirt and making things worse. As I mentioned before I use video drum cleaning spray for this with some success this leaves a non sticky, dry and clean surface.
Yes, it makes a good flame thrower too very effective when you have too many mosquito’s around. ;D

I'll try to find and buy a "video drum cleaning spray". Is there a particular product I should check out?

Now I am really curious...I need to get a WD40 and do some ghost-busting...Isn't there a chance it blows in your hands? ;D ;D ;D