Author Topic: NOS Wire-wound potentiometer cleaning question  (Read 2006 times)

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Offline innkeeper

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NOS Wire-wound potentiometer cleaning question
« on: October 15, 2018, 09:41:28 pm »
I'm looking to clean this NOS wire-wound pot.  it appears like there may have been some kind of lubrication on the wiper area, that has dried out and turned waxy / flaky and maybe and even perhaps even moldy.
I've certainly cleaned carbon pots before with doxit,
I'm looking to how to clean it without damaging it, and also what, if any, lubrication would go into it and where it would go. 
I did notice some dead spots, but not sure if that's due to just the dry lube or oxidation

See pics below.




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Offline coppercone2

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #1 on: October 15, 2018, 09:49:35 pm »
maybe ultrasonic
 

Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #2 on: October 15, 2018, 11:30:15 pm »
don't have access to an ultrasonic cleaner at the moment, though if people have had good experience with it for this purpose id consider getting my hands on one.
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Offline ogden

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #3 on: October 15, 2018, 11:50:08 pm »
Try IPA alcohol + brush first.
 
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Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #4 on: October 16, 2018, 12:00:04 am »
if it is of any help
I just put it under the microscope to get a better look at that white stuff, and it's all fiberous looking strands and looks to me like a white mold. I did find a thread on another forum where this is talked about for the exact same potentiometer having this issue, so seems to be a common problem with these RA30 pots that are NOS.. I didn't see where anyone came up with a good cleaning solution.  my microscope doesn't have a camera, but I do have one of those cheap USB microscopes I can try and get a picture of it with if anyone wants a close up view.

the spec is a linear pot 4W with a 280 degree effective rotation and a 300 degree mechanical rotation... id love to clean this nos part and use it, but, I'm open to finding a modern replacement at a reasonable cost. The 280 degree effective (electrical) rotation is critical due to it being used on a calibrated scale.
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Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #5 on: October 16, 2018, 12:04:37 am »
Try IPA alcohol + brush first.
Does ipa alcohol work well to remove mold deposits?
I know I hadn't posted what I had seen under the microscope before you replied with the ipa idea.
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Offline ogden

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #6 on: October 16, 2018, 12:09:11 am »
Does ipa alcohol work well to remove mold deposits?

I would just try. It takes less time than to post forum message. If does not work - then obviously you have to look for other ways of cleaning.
 

Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #7 on: October 16, 2018, 10:45:58 am »
I could certainly experiment. But I really don't wanna play guess what might work on this part.
Hobbyist and a retired engineer and possibly a test equipment addict, though, searching for the equipment to test for that.
 

Offline ogden

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #8 on: October 16, 2018, 11:11:52 am »
I could certainly experiment. But I really don't wanna play guess what might work on this part.

Well, then take samples of dirt/grease/fungus, send to laboratory and ask them to determine best possible cleaning solution :horse:

Trying most popular cleaning fluid in the electronics industry shall not be considered as experimenting. After all IPA alcohol shall be in your toolbox besides screwdriver and soldering iron. Other option would be to try any contact cleaner in case you have one.
 

Offline xavier60

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #9 on: October 16, 2018, 11:30:27 am »
Be sure to lubricate it after cleaning. I have good success with Synthetic PAO oils or PAO based grease like Super Lube.
My go to solvent is mineral turpentine.
Hioki AS100D vom, HP 54645A dso, Fluke 87V dmm, AN8008 dmm, Agilent U8002A psu,  FY6600 function gen, New! Brymen BM857S-(With Battery)
 
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Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #10 on: October 16, 2018, 03:36:00 pm »
Be sure to lubricate it after cleaning. I have good success with Synthetic PAO oils or PAO based grease like Super Lube.
My go to solvent is mineral turpentine.
What areas should be lubricated? I am assuming the shaft but, should the area where the wiper hits the wires be lubricated as well?
Hobbyist and a retired engineer and possibly a test equipment addict, though, searching for the equipment to test for that.
 

Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #11 on: October 16, 2018, 03:46:27 pm »
I found something interesting today digging around in some older documents. seems that the wire wound resistor is wound around material made up of Phenol-formaldehyde which is degraded by the white rot fungus Phanerochaete chrysosporium.  I'm positive this is exactly what I am seeing here. 

I will say this is the first seeing this on phenolic, but, seeing that the whole unit this pot is going into is also made of phenolic pcb's id hat to see this get into the rest of the unit.

Anyone has experience with this and how to deal with it so it doesn't keep happening.
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Offline Gyro

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #12 on: October 16, 2018, 06:08:16 pm »
I think IPA is pretty destructive to all forms of microorganisms due to its strong dehydrating properties. It will suck all the water out of the cells.
Chris

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Offline xavier60

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #13 on: October 16, 2018, 08:13:28 pm »
Be sure to lubricate it after cleaning. I have good success with Synthetic PAO oils or PAO based grease like Super Lube.
My go to solvent is mineral turpentine.
What areas should be lubricated? I am assuming the shaft but, should the area where the wiper hits the wires be lubricated as well?
Mainly lubricate the where the wiper contacts the resistive element.
If the shaft rotation feels good, it's best to leave it alone because it is usually lubricated with something with high viscosity to give it a smooth glide feel. It is difficult to find out exactly what to use.
 If the feel of the Pot isn't important then just Super Lube oil or grease can also be used.
Hioki AS100D vom, HP 54645A dso, Fluke 87V dmm, AN8008 dmm, Agilent U8002A psu,  FY6600 function gen, New! Brymen BM857S-(With Battery)
 

Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #14 on: October 16, 2018, 08:55:36 pm »
what I went for was to first use isopropyl alcohol for both de-grease and cleaning and to kill as much of the fungus as I could, using a soft brush to get as much of it off as possible. then followed that up with a mix of white vinegar with a little salt, this helped remove any tarnish from the metals, and also helped kill fungus as well. then gave it a quick rinse with water and dried it with compressed air.
looks good so far, will post some pics later.

so i did disassemble the pot to clean i. under the wiper that connects to the windings is a brass plate and a wiper that connects it to the center pin.
it seems to have been lubricated with some dark grease, like axle grease. but had gotten very waxy.

what i have that might be closer to what was there is some silicone/PTFE grease. I also have fader lube, but only the spray kind, but it is quite thin, I might use it but not spray it on, but spray it onto an applicator and put it on with that.
Hobbyist and a retired engineer and possibly a test equipment addict, though, searching for the equipment to test for that.
 

Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #15 on: October 16, 2018, 09:37:52 pm »
Mainly lubricate the where the wiper contacts the resistive element.

Are you sure xavier? or are you going on experiences from carbon pots....

I know the non-resistive wiper that wipes against the brass plate that connects the wiper to the center pin is grease covered. Are you sure that the wiper that brushes the wire windings is lubricated?  Id think if it is, the lube would need to be quite special as to not soak into the phenolic the wire is wrapped on and cause damage over time.

plus being a 4w pot, it might get a bit toasty.
« Last Edit: October 17, 2018, 09:24:16 pm by innkeeper »
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Offline xavier60

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #16 on: October 16, 2018, 10:27:50 pm »
I'm never really 100% sure of anything :-).
I'm going by my experience with other types of pots and switches with sliding contacts that always perform better with a suitable lubricant that reduces wear and tarnish.
There is another problem that can be caused by lubricants of mineral origin, wax content, which tends to form and insulating layer on contacts.
Synthetic lubricants are expected to have no wax content.
Hioki AS100D vom, HP 54645A dso, Fluke 87V dmm, AN8008 dmm, Agilent U8002A psu,  FY6600 function gen, New! Brymen BM857S-(With Battery)
 

Offline xavier60

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #17 on: October 16, 2018, 10:34:43 pm »
Hioki AS100D vom, HP 54645A dso, Fluke 87V dmm, AN8008 dmm, Agilent U8002A psu,  FY6600 function gen, New! Brymen BM857S-(With Battery)
 
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Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #18 on: October 17, 2018, 01:13:51 pm »
after some nosing around a bit more, and seeing some pics of disassembled clarostat wirewound pots ... I've gone with using archer Professional Gel Lube (same as super lube from what i understand) to lube the washer at the end of the shaft, the brass plate, and brush that connects to the center pin, and lastly lubricating the winding / brush area. pot works smooth as you would expect it to with no dropouts.

The Lube itself is synthetic with PTFE, (PAO),  doesn't attract dust, and has a very wide temperature range -65 to 650F, it's quite thick and stays put and is non corrosive. seemed like the perfect lube for a 4w wire wound pot that will be placed in service with some tube equipment.  I don't have to worry about it getting liquid when it gets hot, or gumming up over time, or gathering contaminants. 

I did consider the various deoxit choices, and nye reolube. seemed to me the deoxit lubes were too thin for this particular pot and they nye options seem to be good but didn't nessisarly offer me anything extra over the super lube / professional gel lube to justify 50 bucks and higher for a small tube.

I believe this is pretty close to what the factory did but with modern lube. oh for anyone interested, I found a date code in the pot 13th week of 1936.   nice to bring something that old back to life.. and it's going into a pice if vintage test gear mode with vacuum tubes, a Sprague TO-6A

« Last Edit: October 17, 2018, 09:28:16 pm by innkeeper »
Hobbyist and a retired engineer and possibly a test equipment addict, though, searching for the equipment to test for that.
 
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Offline xavier60

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #19 on: October 17, 2018, 05:17:46 pm »
In case others were also suspecting, there is a mistake in the current data sheet for SUPER LUBE® MULTI-PURPOSE SYNTHETIC GREASE.
Super Lube representative says the base oil viscosity is cSt @ 100°C: 8, SUS @ 40°C: 350  or simply ISO grade 68.

« Last Edit: October 17, 2018, 05:49:12 pm by xavier60 »
Hioki AS100D vom, HP 54645A dso, Fluke 87V dmm, AN8008 dmm, Agilent U8002A psu,  FY6600 function gen, New! Brymen BM857S-(With Battery)
 

Offline SilverSolder

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #20 on: October 18, 2018, 02:34:32 am »
A completely crazy idea that might not work! - but mold/mildew can be terminated with a product like Wet and Forget mold and mildew remover.  The active ingredient in Wet & Forget is Alkyl Dimethyl Benzyl Ammonium Chloride.  It is a surfactant and disinfectant. It is often the active ingredient in anti-bacterial wipes.  It is not aggressive (like bleach, lye, etc.) and doesn't seem to degrade the materials it is used on (no guarantees though!).

I have used it in diluted form to clean mold out of the interior of a car, with good results - it hasn't come back, and it hasn't harmed the automotive vinyl or fabrics.
 

Offline innkeeper

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Re: NOS Wire-wound potentiometer cleaning question
« Reply #21 on: October 23, 2018, 12:12:10 am »
end result....if anyone wants to see any pics on the steps involved let me know

« Last Edit: October 23, 2018, 11:02:03 pm by innkeeper »
Hobbyist and a retired engineer and possibly a test equipment addict, though, searching for the equipment to test for that.
 


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