Concentric potentiometer stuck

[diko2]

Hi,

I've just got a Soundcraft 8000 with a lot of concentric potentiometer stuck (the gain and the frequency moving  together)

Did anybody got a tip to make them free again?

I don't even know what is the cause of this trouble.

Thanks

Morgan

 

[Script]

Don't know the specific pot, but had similar problem once. I opened the pot, cleaned the shaft with alcohol and put it back together again. The resin had tried stiff. If that doesn*t work/not doable, you need a new pot.

On another stuck pot the feeler had come off. Needed a new pot.

 

[JohnRoberts]

Perhaps too much of the wrong pot lube has seized up the two shafts

JR

 

[diko2]

Thanks for your replies.

I've read that alcohol can be bad with plastic track. Is it true?

I've used contact cleaner for years with potentiometer before i was told that it was the worst thing to do.
So now i really don't know what to do with those.

thanks

 

[JohnRoberts]

Thanks for your replies.

I've read that alcohol can be bad with plastic track. Is it true?

I've used contact cleaner for years with potentiometer before i was told that it was the worst thing to do.
So now i really don't know what to do with those.

thanks

The pot manufacturers I've talked with about this discourage adding any foreign chemicals into their pots.

Perhaps experiment on one or two first, to determine a solvent (or lubricant) that does the least harm. .

Are replacement pots available?

A liquid spill could cause this, perhaps corrosion of the metal shafts. The remedy may depend on the cause. If the sticky pots are localized in just one area, perhaps a spill, if all the pots over a wide area are sticking, perhaps corrosion, from a humid environment. 

JR

 

[Script]

Just be careful when you open and clean a pot. Your pots are non-functional, so there's little to lose.. But don't use anything containing acetone (propanone), cos it indeed dissolves plastic. I'd start with the worst pot and try to figure out what's wrong with it.

 

[abbey road d enfer]

I've just got a Soundcraft 8000 with a lot of concentric potentiometer stuck (the gain and the frequency moving  together)


I don't even know what is the cause of this trouble.

Either rust or caked lubricant; in both cases a dose of WD40 should do the job. Just make sure you put it on the shafts, not inside the pot. In any case, check that it's not the knobs that are glued together by grime.

 

[diko2]

So i've tried on  one pot with isopropyl alcohol and it works very quick and well.
Didn't need to open the pot to do this.
Now the inner pot turn perfectly as new.

The question is:  is it really bad for the pot.

I've got  40 potentiometers stuck and maybe 10 more that turn with difficulty.

The pot are Preh 2X100k.
The stuck one are all over the desk.

I'm not that good with chemistry: is isopropyl containing acetone?

I've also found this:
http://store.caig.com/s.nl/sc.2/category.293/.f

Would it be better than isopropyl?

You told about lube, is there a type that is better for this?


Thanks

 

[abbey road d enfer]

So i've tried on  one pot with isopropyl alcohol and it works very quick and well.
Didn't need to open the pot to do this.
Now the inner pot turn perfectly as new.

The question is:  is it really bad for the pot.

I've got  40 potentiometers stuck and maybe 10 more that turn with difficulty.

The pot are Preh 2X100k.
The stuck one are all over the desk.

I'm not that good with chemistry: is isopropyl containing acetone?

I've also found this:
http://store.caig.com/s.nl/sc.2/category.293/.f

Would it be better than isopropyl?

You told about lube, is there a type that is better for this?


Thanks

Alcool will partially dissolve the lubricants that are necessary to the proper operation of the pot, that's why I suggested using a standard lubricant, such as WD40, that will restore the fluidity of the original lubricants.
Deoxit is nice for cleaning the resistive track, but I'm not sure it can free the shafts. You have to give it a try.

 

[diko2]

Ok i will try that.

Thank you all.

Cheers

Morgan

 

[CJ]

sometimes you can free the shafts with chemicals but when the solvent evaporates, the shafts freeze up again or get hard to turn,

maybe turn board upside down and flood main chambers, wait for the chemicals to leach out old grease,

problem with this is removing the board and the ten million knobs,

 

[abbey road d enfer]

sometimes you can free the shafts with chemicals but when the solvent evaporates, the shafts freeze up again or get hard to turn,

maybe turn board upside down and flood main chambers, wait for the chemicals to leach out old grease,

I wouldn't recommend doing that, since it's just the shafts that are stuck.

problem with this is removing the board and the ten million knobs,

Soundcraft 8000 is fully modular, so it's not a major issue.

 

[bruno2000]

I would try some "fader lube".....
Best,
Bruno2000

 

[Whoops]

I would take all knobs out, unmount front panels until you have access to the bare concentric pots.

Check the pasts that are stuck, is it metal to metal shafts, metal to plastic?
If so I would used Caig D5 or F5 to make them move again , clean them, and after regrease it with a silicon based grease in spray.
Be careful when you do this, these procedure is just if the stuck parts are Outside the Pots. Dont apply any grease to the Pots Resistive track or wiper.

You need some grease (thicker lubricant) on the Pots mechanical rotating parts in order for them to continue to turn well in the future.

I would not advise WD40 at all as it is a really thin lubricant, it will make the metal parts move again , but will dissolve all the grease and in some weeks after it evaporates metal parts will be stuck again and actually the problem will get worse.
I guess you could use WD40 to make them move again, clean it ,  and then Regrease it, the problem is that if WD40 enters the resistive tracks or any electronic parts it is quite unfriendly to those sections something thats not the case with Caig D5 or F5.

 

[CJ]

if you really want to restore this thing to it'sorigial form thenn there is no better way than to replace the pots,

 

[Monte McGuire]

Hi,

I've just got a Soundcraft 8000 with a lot of concentric potentiometer stuck (the gain and the frequency moving  together)

Did anybody got a tip to make them free again?

I don't even know what is the cause of this trouble.

Just to avoid catastrophes due to language subtleties, it's important to determine if the knobs are simply stuck together or that the actual potentiometer shafts are stuck together, not just because the knobs are coated with something that makes them stick together. The first thing that comes to mind is that someone dumped a large amount of liquid (a beverage?) onto this console, the liquid dried, causing things to stick together.

If you remove the knobs, do the pot shafts turn easily? Does it appear that the console has been covered in some sticky gooey substance? If it's a foreign contamination problem, then applying solvents to the pot shafts may just further drive the contaminant into the pot. Maybe a slightly damp cloth or towel can be used to carefully free the contaminant that makes the shafts stick together without driving it deep into the pot itself.

Practically, the cost of replacing these sorts of semi-custom pots will probably far exceed the value of the console, so if this is needed, or if solvents are used that drive the problem deeper into the pot, you might as well throw the console out now. And, this might be the reason that you now have possession of it - it's either been doused too thoroughly or repaired too hastily and sloppily.

So... start slowly and simply remove the knobs. What do you see? Is the problem actually the pots, or just a surface coating of gunk that might be able to be removed if you work carefully? Is the sticky stuff also on the front panel? If so, what seems to loosen or remove it - perhaps a warm, slightly damp cloth? Do you even need anything stronger? Has someone cleaned the unit? For example, if you see no dust underneath the knobs, then perhaps someone already doused the console in water or solvent?

More information!!

 

[mjrippe]

I've just got a Soundcraft 8000 with a lot of concentric potentiometer stuck (the gain and the frequency moving  together)


I don't even know what is the cause of this trouble.

Either rust or caked lubricant; in both cases a dose of WD40 should do the job. Just make sure you put it on the shafts, not inside the pot. In any case, check that it's not the knobs that are glued together by grime.

No Abbey No!  Keep WD-40 as far away from audio and electronics as possible!  I know you said to keep it out of the pot - but it is a thin solution and very hard to control.  IPA (isopropyl alchohol - not the beer) is a much safer cleaner/solvent.  Water Displacement formula 40 has no place in electronics unless they have been exposed to water.  We used it to displace water from circuit boards from a flooded studio but then had to flush the boards thoroughly with IPA to remove all the WD-40!

WD-40 is useful for nuts and bolts that have siezed, but even questionable in that regard: http://hackaday.com/2016/05/17/beyond-wd-40-lubes-for-the-home-shop/#more-204952

 

[diko2]

Hi everybody,

Thank you all for your replies.
It's interesting to see that there is so many point of vue.

After a deep inspection on the board it looks that it was some greasy thing  that stick the inner pot.
Maybe the "too much of bad lube" scenario was the good one.

So i free the 40 bad pots with  a small drop of isopropyl on the shaft (at the junction of  the inner and outer).
Wait 1 min and then try to make it turn.
The first turns were very difficult and after maybe 10 turn it's free as new.

Listen to all EQs: everything work fine. Hope that it will last.


Cheers

Morgan

 

[Script]

Glad to hear that you got them moving again. Should they get stuck again, try opening them, cleaning them properly with isopropyl and then apply a bit of new proper fader lube as suggested above.

 

[Gene Pink]

Hi everybody,

Thank you all for your replies.
It's interesting to see that there is so many point of vue.

And here's yet another one.

After a deep inspection on the board it looks that it was some greasy thing  that stick the inner pot.
Maybe the "too much of bad lube" scenario was the good one.

So i free the 40 bad pots with  a small drop of isopropyl on the shaft (at the junction of  the inner and outer).
Wait 1 min and then try to make it turn.
The first turns were very difficult and after maybe 10 turn it's free as new.

Listen to all EQs: everything work fine. Hope that it will last.

It won't. Alcohol is quite volatile, and will evaporate soon, leaving behind the thick gunk that you started with. But you are treating it in the right place, nowhere near the innards.

I believe your original lube was a petroleum based grease, and not all that highly refined, meaning it was a blend of many different viscosities, many different hydrocarbon chain lengths.

Over, what, 30 years?, the shorter hydrocarbon chain, more volatile components have evaporated, leaving behind the heaviest components, basically something akin to tar. Constant use helps prevent this, as turning a knob occasionally keeps them all mixed, where non-use, especially when stored at higher temperatures seems to allow the lighter components to migrate to the surface where they can evaporate, and they do.

I hesitate to give advice on what to do with your new cherished console, but if it were mine, I would just use a tiny bit of light oil, 3-N-1 or similar, to at least get something resembling a blend of a useable viscosity back in there. If a pot doesn't free up, add a touch of a solvent, I use toluene. Just don't drip whatever solvent you use on the console paint, if it doesn't dissolve it, it will dull it. A piece of cardboard with a pot-thread sized hole helps with this.

The toluene will evaporate quickly, but it helps to break any crusty surface skin preventing the light oil from getting in where it needs to mix with the tar.

I have a Soundtracs 40x12 monotor board that I have to do this to on occasion, while not concentric knobs, it has those wimpy little 4mm white plastic D-shafts, and they get impossible to turn, the knob will split first.

I put a marker dot under the knob on the mounting nut, to keep track of pots that I have done this "back-woods-treatment" to, the next time around, it is rarely the same ones.

Like you, I have no intention of pulling every channel, unsolder every pot, disassemble and rebuild, and put it all back together. Screw that nonsense.

Gene