How to clean vernier potentiometers with ball bearings - Page 1
Forum section: electronics / repair

author: Unknown
author_rank: Unknown
timestamp: February 22, 2019, 07:48:32 pm
content: I'm trying to restore an ancient Gamma Scientific X-Y plotter (analog!). Looks like it was in a filthy basement for decades (lots of mouse droppings, nesting materials, and dead insects inside it).It cleaned up pretty good (I didn't take any photos of what it looked like when I got it), but the X and Y gain pots don't move when I turn the verniers. They're the type with three ball bearings. Looks like one of them has crud on it.What's the way to clean these? I can do Deoxit but I think the bearings need some oil lubrication, right?

author: Gyro
author_rank: Super Contributor
timestamp: February 22, 2019, 09:04:46 pm
content: I'd be a bit careful because anything you introduce into the bearing area will work it's way down to the (look like carbon) potentiometer tracks, contaminating them.The balls themselves need frictional rolling contact with the center spindle and metal rim to provide the 'reduction gear' action (dragging the black plastic hub around). I think they would have originally been run dry.Probably best just to remove any visible debris, maybe a cotton bud very lightly moistened with IPA, and then check whether there is any issue with electically noisy pot wipers that require further attention.P.S. Re-reading, the sticking pots could be down to either contamination of the balls or the plastic hubs sticking, the above gentle cleaning should hopefully tell you which.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: February 25, 2019, 03:01:15 am
content: One of the tricky things with equipment of that vintage is how many different materials were used for the various pieces. They really hadn't settled on the relatively small number of somewhat identifiable plastics they use now. This takes some time and easy-going to decide what is compatible with the base materials while dissolving only the things you want cleaned away.Watch out for reactions with contact surfaces, paint, silk screens, other labeling, etc.When I've had to do similar work, which of course was with very different equipment, I found that I needed to use several different chemicals in sequence. The most similar part I worked on were concentric wirewound potentiometers on the same shaft as multipole switches. The grease dried up, but they also have complex mechanical stackups.Eventually after trying other things to get the shafts loose, cleaned, and re-lubricated I did this:1. WD-40 for dissolving the grease. Spray in, work it for a while, and then spray out. Absorb with paper towels, etc.2. Alcohol for dissolving out the WD-40.3. New shaft lubricant. I happened to use sewing machine oil.4. Contact cleaner that is safe for plastics to clear away anything that flowed in from the alcohol.

author: David Hess
author_rank: Super Contributor
timestamp: February 25, 2019, 03:27:35 am
content: I have cleaned a few like that. I used plastic safe contact cleaner which is naphtha and a lubricant for the potentiometer elements so it is safe if it gets into the potentiometer. After the naphtha evaporated, I added some heavy oil to the ball bearings.