wirewound pots restoration and tactile feel - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: March 27, 2021, 10:45:38 am
content: So I redid the wirewound single turn potentiometers on my harrison HP supply. They were filled with real nasty black crud. I used ultrasonic on them for ~15 min and used a small brush to scrub them out after 6 min in, then sprayed with goo-gone, let it sit for a few min then back in the ultrasonic and then wiped with a Q tip. Then I sprayed it with deoxit immediately after to discourage any oxidation from the water and put deoxit grease in there on top of the coil with a q tip to push it in there, put a generous amount, traversed the wiper a few times and put it back together and soldered it back into place, so I can't take pictures unless I take apart another similar HP unit (which I may, the 3310B might get a potentiometer revitalization if the replacement PCB works)The feel is very springy now. They measure OK but it feels almost like its like a car riding on a bumpy road.The only thing is, I am used to 10 turn potentiometers, these are single turned ganged potentiometers (fine and coarse on top of each other).The contact just rides on top of the wire coil, it does not have some kinda slide element like a variac.Are they supposed to feel a little bit vibratory? When I compare to the 10 turn helipot or something, it feels much more averaged/fine. I am just wondering if you are supposed to pack these potentiometers with a more sticky grease, the deoxit 260DL grease reminds me of vasoline more then anything, but it has deoxit in it. I was imagining what it might feel with different greases, i.e. wd40 all purpose grease, or silicone dielectric grease..I did service a cheap rheostat before with silicone dielectric grease (a power component that functioned in the same way, but it was open to the chassis, real cheap piece of shit), and that one felt even worse then this HP potentiometer, and the really really tacky silicone CRC grease only improved it slightly.I could see the WD-40 all purpose grease maybe making it a little smoother (its mad slick, I put it in a magnetic drill and it felt like it was gliding on the bore handle) but it almost seems that in this case like this is purely a consequence of wire geometry.. I want to say the 10 turn trimmers have finer wire.. so you feel them less.But, I thought maybe the black crud that was in there originally was some kind of grease loaded with something, to make it more smooth by filling the gaps or something like that.So in a nut shell, are these single turn wire wound potentiometers supposed to run with a little bit more vibration or did I loose some kind of opportunity?I thought maybe to get deoxit fadergrease.. but generally I see people recommending silicone, perhaps out of concern for the plastic parts.?I think my cleaning was really good, it was shiny in there under light before regreasing.. so I don't think its a problem related to hygiene. Ware maybe?The sensation I am explaining maybe can be likened to imagining yourself doing a very small zipper (clothing zipper). It is MUCH less noticeable on the ten turns I have, but I don't think I ever serviced them.Also, does anyone have any tips on bending them open? I broke the bend flap on the thing holding the two pots together, but this thing I am describing is not related to that, because they function independant of each other, and they did the same thing when not soldered it, and they do not align each other or anything like that, it was just there to make it easy to grab out of a box on the assembly line with the two units being joined together and aligned correctly for soldering. I tried to bend it up slightly with a knife then grab it with smooth jaw stub pliers and bend it up, but it broke. I have various luck with this, mainly related to DIP chips, and battery holders.. if you get a expensive one usually it lasts ALOT longer in terms of bending then a cheap one, which seems brittle... but is there a good technique other then be more gentle?And right, I feel like the potentiometer felt.. less vibratory before I serviced it.. but some how shittier/scratchy/dirty. I prefer how it feels now then how it felt before, but I think I noticed it is running with more vibration with the new grease. Typically I was only using this stuff to grease crimps and stuff like that. Like when I was deciding if I should clean it, it was 'defiantly' but when I finished it was like 'well thats a new noticeable mechanical parameter'. I thought maybe when they get mad old and disgusting it some how smooths it out, but I don't know what it felt like in 1960.Oh right and it did have electrical problems with not being smooth electrically, so it IS a good thing I cleaned it, its supposed to be a precision supply, and inside some of the parts were super worn (i.e. corroded transistors).my theory: I noticed on my stove extraction hood when I pried off a panel, there was a thin amount of really old grease in there under the plastic (you had to snap plastic pop in rivets to get in there), and the old grease was almost like.. a rubber membrane. I thought it might have been glue at first but I don't think so. I noticed this on a deep fryer also. I thought maybe in the potentiometer as it got old some kind of highly polymerized grease formed on the wiper that acted as a kind of damper to mask the vibrations that it produces when its clean (so its like a rubber washer developed/grew under the wiper that smoothed things out).