Reconditioning Bourns 10-turn potentiometer

[motocoder]

I have been working on repairing an HP 6177C DC Current Source. I just found and fixed the major electrical problem with it (bad zener diode), and it appears to be working well now.

Next up, I will start working on restoring the electro-mechanical components, i.e. the switches and precision potentiometers. There is a Bourns 2K 10-turn pot that is used to adjust the current. Compared to a replacement for one of these that I put in an HP 6115A, this one is very hard to turn. I have heard that it is possible to recondition these potentiometers. Can someone describe for me what the process is for that?

Thanks

[retrolefty]

Well I quick thing to try is to see if applying some penetrating lubricant to the front bearing/bushing and give it time to wick into the bushing might free up the pot if that is the problem.

[motocoder]

Well I quick thing to try is to see if applying some penetrating lubricant to the front bearing/bushing and give it time to wick into the bushing might free up the pot if that is the problem.

Hi retrolefty - I was worried that might make it's way into the resistive element, and cause issues there.

[motocoder]

Well, any further replies will be for posterity. I popped it open, but when I went to put it back together, part of the plastic that holds the clip on broke...

[schopi68]

I've just replaced this Bourns 10-turn pot in two of my hp-supplies (6114a and 6827A) - i've opened one of these to clean it up. After short ultrasonic removal of the old lubricants and relubing it i could sucessfull reassemble it to a working state.

BUT: turning it is still hard, it did not change much. Todays replacement models are using another type of shaft sealing. Todays ones are easy to turn, but they have a noticeable axial clearance. The old ones do not have this clearance - and i think they have a better sealing. So from a today's perspective it is not easy to say if the old ones were easy to turn when they were new.

[edpalmer42]

Many 10-turn pots have a brake on them to prevent them from moving.  You didn't accidently leave the brake on, did you?   

Ed

[motocoder]

Many 10-turn pots have a brake on them to prevent them from moving.  You didn't accidently leave the brake on, did you?   

Ed

No, it turned just fine. The grease was just all dried up and crusty, so it was just a bit hard to turn. I've since replaced it with a new one, which is working great.

[nctnico]

BUT: turning it is still hard, it did not change much. Todays replacement models are using another type of shaft sealing. Todays ones are easy to turn, but they have a noticeable axial clearance. The old ones do not have this clearance - and i think they have a better sealing. So from a today's perspective it is not easy to say if the old ones were easy to turn when they were new.

Where did you get the replacements?

[motocoder]

BUT: turning it is still hard, it did not change much. Todays replacement models are using another type of shaft sealing. Todays ones are easy to turn, but they have a noticeable axial clearance. The old ones do not have this clearance - and i think they have a better sealing. So from a today's perspective it is not easy to say if the old ones were easy to turn when they were new.

Where did you get the replacements?

It's Bourns part number 3540S-1-202L. I got the replacement from Mouser:

http://www.mouser.com/ProductDetail/Bourns/3540S-1-202L/?qs=%2fha2pyFaduiwM23ZqLo0TC54lgzp9wd3jTkF5bFAaXdaFS0VmbsebA%3d%3d

DigiKey also carries them:

http://www.digikey.com/product-search/en?keywords=3540S-1-202L

Vishay also makes a good replacement, which IIRC is about half the price.

[schopi68]

Where did you get the replacements?

the same for me, i've ordered the replacement from mouser.