Reconditioning Bourns 10-turn potentiometer - Page 1
Forum section: electronics / repair

author: motocoder
author_rank: Unknown
timestamp: July 02, 2015, 04:30:12 pm
content: 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

author: retrolefty
author_rank: Super Contributor
timestamp: July 02, 2015, 04:46:01 pm
content: 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.

author: motocoder
author_rank: Unknown
timestamp: July 02, 2015, 04:49:46 pm
content: Quote from: retrolefty on July 02, 2015, 04:46:01 pmHi retrolefty - I was worried that might make it's way into the resistive element, and cause issues there.

author: motocoder
author_rank: Unknown
timestamp: July 02, 2015, 05:45:38 pm
content: 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...

author: schopi68
author_rank: Regular Contributor
timestamp: July 10, 2015, 02:29:18 pm
content: 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.

author: edpalmer42
author_rank: Super Contributor
timestamp: July 10, 2015, 02:53:58 pm
content: 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

author: motocoder
author_rank: Unknown
timestamp: July 10, 2015, 03:28:34 pm
content: Quote from: edpalmer42 on July 10, 2015, 02:53:58 pmNo, 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.

author: nctnico
author_rank: Super Contributor
timestamp: July 10, 2015, 07:47:54 pm
content: Quote from: schopi68 on July 10, 2015, 02:29:18 pmWhere did you get the replacements?

author: motocoder
author_rank: Unknown
timestamp: July 10, 2015, 10:11:39 pm
content: Quote from: nctnico on July 10, 2015, 07:47:54 pmIt'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%3dDigiKey also carries them:http://www.digikey.com/product-search/en?keywords=3540S-1-202LVishay also makes a good replacement, which IIRC is about half the price.

author: schopi68
author_rank: Regular Contributor
timestamp: July 11, 2015, 01:18:31 pm
content: Quote from: nctnico on July 10, 2015, 07:47:54 pmthe same for me, i've ordered the replacement from mouser.