Sealed Potentiometer Lubrication

As a friend's father used to say, "I've never been intimidated by a rivet." Drill them out, replace with screws to reassemble.

Umm, did the op say he was putting OIL in the pots ?? That should settle the matter :-)

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I use a hypodermic needle, like I use to refill ink cartridges, filled with Naptha to restore nosiy pots. Usually works, maybe 90% of the time. THe Naptha penetrates into almost anything.

My method of doing this is to get a pencil soldering iron with small long tip. Melt a hole in the case carefully and slowly. When you break through, be sure to turn the pot back and forth so the slag does not jam the pot. Then spray Caig pro gold or such into the hole and work the pot back and forth. I usually melt the hole opposite the terminals if possible allowing room for the resistance film.

bob

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

that washes away the shaft grease,right into the pot.

when I was working at TEK field service centers,that is exactly what I used to do. I made up a fiberglass rod with a coupler on the end holding a small drill bit(to get into tight areas without taking apart the whole scope),and hand-drilled small holes in the sides of the black Bourns modpots (multisection!). I had taken one apart to find the best place to drill without hitting the rotor,and you have to be careful when you're just about to break thru,and pull OUT the last bit of plastic so it doesn't get carried into the pot.Then I fixed a hypo needle to the plastic spray tube on the tuner/lube TEK used to supply,and after the spray cans of that went away,I made up a spray can with a brass fitting from an old inner tube soldered to the top,so I could fill the can with TEK's cleaner-lube that came in a bottle,it had Cramolin in it,along with some Freon solvent.Then I could pressurize it with a bicycle pump.The needle slipped easily into the small drilled hole,and a squirt would do the job. I didn't bother resealing the hole. It worked very well,and saved customers a lot of money,and me a lot of time.

"Rheilly Phoull" wrote in news:kNGdnYAf5MqwQ7PWnZ2dnUVZ snipped-for-privacy@westnet.com.au:

easier said than done.

I now use Radio Shack's tuner cleaner/lube 64-4315

it contains mineral oil.

There seems to be a rubber O-ring or other seal inside. I couldn't get very much cleaner past it. I don't think there's any grease left in the old pots, but you're probably right about it for fairly new pots.

I was going to use a Dremel drill, but I guess you're a drill in a pin vice should give better control. Thanks for saving me from that disaster.

That main thing is that you've confirmed that drill and squirt is the most practical way to deal with this.

Good point. Any clue as to the best place to drill? Obviously on one of the sides.

I have plenty of syringes and the usual electronics chemistry set. I like to use alcohol to do the initial cleaning followed by a drop or two of mineral oil. The big advantage is that it doesn't soften most plastics. I have some Cramolin, so maybe that's a better cleaner (because it removes various oxides).

Clever, but I don't plan to make this exercise a regular habit. A simple syringe should work except for awkward locations. Also, it's fun terrorizing visitors and customers with my collection of syringes.

Thanks much. I'll try it after I find and dissect an old pot to see where to drill.

I don't mind drilling out the rivets. It's the rest that has me worried. There are 4 rivets per pot. I just counted 12 pots per instrument. I have 3 Wavetek/SSI 3000b service monitors to fix:

all of which have the same problem with intermittent pots. That's 144 rivets. Drilling is the easy part. How am I suppose to get them back together? I'm not sure but the rivet holes appear even smaller than a

Yes, I did. A different problem with many pots is rust, dirt, dust, and crud causing the shaft to jam or turn roughly. There are various ways to lube the shaft, but one of the easiest is an adapter that screws onto the mounting threads, which directs the oil around the shaft under pressure:

I built my own, which is similar to the one in the photo except that it's brass, longer, and ends in a bicycle valve. I run some solvent (usually just alcohol) through the pot first, then follow it with some oil or grease. Incidentally, I've had some spectacular failures from using too much pressure.

What I tried to do unsuccessfully was to use the same device to deliver a load of contact cleaner into the Mod Pot sealed potentiometers using the aformentioned device. It didn't work.

Hopefully, that should settle your manner.

Coleman white gas camp fuel is basically naptha. Is that what you use? Seems a bit strong and overkill to me for pot cleaning.

I have two friends that are diabetics that give me some of their old syringes. I grind off the sharp point with bench grinder, and clean up the burr by polishing and forcing a fine stainless wire down the bore. The syringe needle is much shorter than the common ink cartridge fill syring, but is also much smaller diameter, which is useful in tight places or through small holes. It looks like this:

Well, I guess you could rivet them back together. By the way, regarding syringes, you don't have to grind off hypodermic needles. You can easily buy dispensing syringes, and needles in any diameter and a variety of lengths.

Agree that you're facing a big job, and one fraught with potential danger.

Use fine ni-chrome heater element wire (stronger than Cu for fine wire) , straightened out , through the holes and twist up tight - who else is going to peer in there ?

From my experience of cubic form / rivetted pots is problem due to too much lubrication, it bleeds, over time, from the bush area grease down onto the track degraded to an oil, open up and clean out with meths

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

On the black modpots,the resistive element is brown,and is exposed on one side,and I drill about 3/32" (rough guess from memory) back from the brown element,on the centerline.The case is circular on the inside,so centerline is the thinnest part.

I didn't have much success with the blue modpots that were riveted together.

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

may attack the plastic. use a standard tuner cleaner/lube spray.

I used my Dremel to grind off the sharp on the needle. a cutoff disc will work fine.I didn't use a really fine needle,maybe 1mm.

Force it down the shaft.

Bob,

Do you mean melt the hole at the back of the pot??

Shaun

I frequently just spray the outside with some very light stuff. I have used Bullfrog cleaner that has high vapors. I also just use alcohol maybe with a little light oil. It works sometimes. Most pots can be taken apart, but I have drilled holes before. Sometimes it takes a day or two to settle in.

greg

Chuckle... please pardon my amusement. There are various ways for pots to fail, but for test equipment, wearing out the resistance material or contacts is not one of them. What seems to be happening here is that the grease, oil, or lube used in the pots, mixes with surface scrapings from the resistance material, and turns to tar. Given sufficient time, it hardens into a mound of goo on the resistance material, which causes a "bump" in the rotation. In less extreme cases, the tar is spread over most of the pot, resulting in a "noisy" pot.

Over the years, I've notice that test equipment pots that have *NOT* been used much, are the ones must susceptible to the aforementioned failure. In my case, I have 3 out of 20 adjustments on the front panel that work just fine. These are the pots that I use most (signal level, deviation, volume). However, the other 17 assorted adjustments rarely get moved and have now become a major problem.

I haven't had time to drill and lube my service monitor quite yet. I'll do it in the next few days.