Cleaning potentiometers

Captain Jack

Captain Jack

Retired human
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So my fancy "new" Technics amp has an issue with its volume control. It's a bit crackly and the channel balance changes depending on where the volume is. Clearly, the pot has had it - or at least dirty.

It's a motorised one, so I can't just pick one off the shelf. It's basically this one though the markings on the side are different (592M MAL instead of 602M MAL - I've no idea what the difference is). I found a new one but it's a different part number and the marking on the side are 413M MAL - again, no idea if this makes a difference. The actual unit looks exactly the same. I assume it's the same internally as well but I don't want to spend about £70 on one to find that it doesn't fit.

The pot doesn't seem to have any accessible holes on it to spray contact cleaner into and I am somewhat reluctant to take it apart in case I completely break it, though it might not be that difficult.

Any insights/advice?
 
Unless it is hermetically sealed, spray will get in there if you do it liberally, or make a small hole with the soldering iron.
 
........ reminisces about Carbon Tetrachloride ......
 
If you can remove it and find a way to soak it with the pot side down (don't get it into the motor) then try and find some of this stuff, it may soak into the pot it's self.
CAIG DeoxIT Pot & Switch Cleaner | stewmac.com

I've had to do the same for some audio control boards, I used a small drinking glass and filled it to a bit above the top of the pot, then let it soak for a bit, exercising the pot afterwards work wonders, let the stuff dry out a bit before replacing it back in operation.
 
Channel Hopper said:
Unless it is hermetically sealed, spray will get in there if you do it liberally, or make a small hole with the soldering iron.
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What are the chances of it being airtight? Any easy way to check? Making a small hole is a good idea.
Terryl said:
If you can remove it and find a way to soak it with the pot side down (don't get it into the motor) then try and find some of this stuff, it may soak into the pot it's self.
CAIG DeoxIT Pot & Switch Cleaner | stewmac.com
Click to expand...
Expensive stuff! But I guess it's good. It's fairly easy to get to and dismantle so another thing to try.
 
Servisol Super 10 is the best stuff I have used over the years.
 
In the motorized case, investigate and plan before acting :O) Careful with the motor. If it's a conductive plastic pot type, some cleaning spray\liquids makes things much worse! If carbon type and very old\seen very much use, the carbon track itself may be worn, no amount of cleaning will help. Regarding pots, a replacement if possible is always better than a fix imo.

Use a dedicated electronics cleaning product. Careful with those that contains much\too much lubricants.
My solution to getting cleaner on\in the right places, or through some small opening ...may otherwise spray everything else than the intended part :O) , the needle tip, very simple, very inexpensive, very recommended.

needle.webp
 
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They use to make some stuff called "Tweak" we used it on the sound boards and video fade pots, it didn't have any type of lube in it, but it sure cleaned a noisy pot.

Don't know if they still make it anymore, I haven't been in the studio business for 17 years.
 
Captain Jack said:
Thanks - have ordered this.

Thanks to all for advice. Will let everyone know of what replacement pot I bought :D
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That Servisol will do the job, use the straw and little squirts at a time, wipe off any excess.
 
Perv.

OK, made a start while I am waiting and he's where I am so far. Took apart the pre-amp and desoldered the pot+motor assembly. These are actually two separate parts but are held together by a clamp thing, which is easy to pry apart. Inside is some needlessly complicated set of cogs from the motor to the pot but very tidy nevertheless.

2018-02-11 11.30.31.webp

I now have relatively easy access to the pot and will spray liberally behind the plastic cog... I don't really want to take it apart any further. I notice the mechanism itself has some oil on it. Should I add some sewing machine oil before putting it back together?

While I was there, I thought I'd clean the source selector knob as well. The symptom is that it tends to jump between sources very quickly when I am even not touching the selector. Not usually an issue but... anyway. Desoldered from the main board and took that apart. The contacts were very dirty inside, so I just wiped them with some tissue and sanded it down with some fine grit sandpaper. Do I need to put some Servisol on that or will the above be fine?

However, inside was again this mystery oil. Should I relube it with sewing machine oil or some thicker one? Or will Servisol be enough to keep lubed? (behave, G).

2018-02-11 11.52.01.webp

These old amps are almost a joy to work with. Everything is accessible and simple to service and replace. I dare not open my Onkyo amp, which has a fault with sound output (there is none). Apparently it's an issue with HDMI board, which are very expensive to replace and are not really user serviceable...
 
@CJ
Ref the Onkyo amp - did you try, as I suggested sometime ago, contacting Onkyo UK to see if it is covered by their extended warranty due to there being an inherent design/manufacturing fault in many of the HDMI i/p boards on many of their products of that and similar generation?

Also, on one of the other UK forums (PM me if you don't know which one) one guy posted info on a repair process which involves reflowing the solder under the BGA chips which is the main problem in those i/p circuits.
 
Yeah I read about the BGA chips reflowing but don't really have the guts to do it. I have a hot air gun but that's about it. It's a useless amp without a fix so may as well try it.
 
You don't need any additional oil with Servisol Super 10.
 
Got Servisol today so cleaned everything up. The source selector knob is now perfect. No jumping between sources.

The volume control, while much better (no audible difference in balance throughout the "rev range"), it's still not perfect. While I can't hear the balance difference (my ears are shot anyway), the needle metres do show a difference. Unlike prior to service, it's consistent, though, so a quick balance adjustment generally resolves it.

I will still try to find the new replacement, even if it means spending £70 on it (new receiver on my shopping list next).
 
Captain Jack said:
Got Servisol today so cleaned everything up. The source selector knob is now perfect. No jumping between sources.

The volume control, while much better (no audible difference in balance throughout the "rev range"), it's still not perfect. While I can't hear the balance difference (my ears are shot anyway), the needle metres do show a difference. Unlike prior to service, it's consistent, though, so a quick balance adjustment generally resolves it.

I will still try to find the new replacement, even if it means spending £70 on it (new receiver on my shopping list next).
Click to expand...
There might be a pot to adjust for balance and the same for the VU meters. I doubt It's the volume pot.
 
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