How to clean contacts of a precision resistor decade (0.01%)? - Page 1
Forum section: electronics / repair

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 28, 2017, 09:46:12 am
content: Can somebody give me advice how to clean contacts of a precision resistor decade, without doing any harm to it?I used a dry cellulose swab wiping the contact, but resistance is still unstable (rising slowly)...I'm not quite sure, how to relubricate contacts (I'm not a believer to magic contact cleaner chemistry voodoo). There's still enough grease on the remaining contacts, so I hope it will dispense to all contacts some time later in normal usage.Root problem still remains.Some wiggling the dial helps temporarily, but some minutes later, resistance is increasing again.

author: BU508A
author_rank: Super Contributor
timestamp: March 28, 2017, 09:50:52 am
content: I recommend to have a look at this website:http://thesignalpath.com/blogs/2017/02/01/deoxit-challenge-restoration-of-a-precision-decade-resistor-box/You may find it helpful.

author: VK5RC
author_rank: Unknown
timestamp: March 28, 2017, 10:21:01 am
content: Cleaning wafer switches in an old Tek scope I used IPA on foam tipped swabs (no fluff from the cotton swab) , firstly on the common contact area, then the actual moving contact till a clean swab returned, Both sides. I then used a swab lightly soaked in deoxit as a replacement lubricant - but a decade resistor box is a lot more fussy.In wafer switches I didn't try to get between the fixed contact and the moving piece as I figured I would do more damage. (I have used heavy paper to clean between relay contacts with success.)If I recall correctly, Shariar used quite a bit of deoxit - I didn't use nearly that much and applied it just to the contact areas.Rob VK5RC

author: alm
author_rank: Super Contributor
timestamp: March 28, 2017, 10:26:59 am
content: Caig recommends that critical, low current connections (which in my opinion includes decade resistor switches) be finished with Deoxit Gold G after cleaning with Deoxit D (or any other cleaning method that removes corrosion). If the contacts are not visibly dirty, I just spray a little G5 on them and rotate the switches a couple of times.

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 28, 2017, 12:13:28 pm
content: Deoxit is not very common in Germany, difficult to find...

author: BU508A
author_rank: Super Contributor
timestamp: March 28, 2017, 12:17:08 pm
content: You can find it on Amazon:DeoxIT D100S-2https://www.amazon.de/dp/B0014F110IDeoxit DeoxIT D5S-6:https://www.amazon.de/dp/B0002BBV4G

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 28, 2017, 12:20:10 pm
content: Yes, I've seen the offer on amazon, but we cannot buy from amazon (because of our business guidelines...)

author: Kjelt
author_rank: Super Contributor
timestamp: March 28, 2017, 12:24:50 pm
content: There must be some replacement from Kontakt Chemie, I would sent then an email asking what they have to offer. I know they have multiple cleaners each for their own application.

author: BU508A
author_rank: Super Contributor
timestamp: March 28, 2017, 12:28:45 pm
content: Quote from: carl_lab on March 28, 2017, 12:20:10 pmProbably this shop is accepted by your company's business guidelines:http://www.micro-tools.de/Kontaktreiniger-oxid/

author: BU508A
author_rank: Super Contributor
timestamp: March 28, 2017, 12:30:46 pm
content: Quote from: Kjelt on March 28, 2017, 12:24:50 pmIIRC the volt-nuts recommend Deoxit from CAIG. Not sure, if Kontakt Chemie (I know them well) achieves the same performance.

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 28, 2017, 07:30:57 pm
content: I know Kontakt-Chemie well, but I'm not longer a fan of Kontakt-Chemie since the infamous "Kontakt 60" disaster many years ago.

author: Kjelt
author_rank: Super Contributor
timestamp: March 28, 2017, 07:39:29 pm
content: Quote from: carl_lab on March 28, 2017, 07:30:57 pmwhat was that?

author: mcinque
author_rank: Unknown
timestamp: March 28, 2017, 07:40:05 pm
content: Quote from: carl_lab on March 28, 2017, 07:30:57 pmWhat disaster?

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 28, 2017, 08:01:14 pm
content: Kontakt-60 was very aggressive, and if not washed out carefully after application, contacts were destroyed.Even the original metal can was destroyed by pitting corrosion (that's my personal experience, confirmed by some colleagues).Not exactly the magic agent I want to remain in my precision instruments...http://www.hifi-forum.de/viewthread-84-1094.htmlhttps://www.amazon.de/CRC-Kontakt-Chemie-Kontaktspray-100ml/dp/B001CRC22Y"Ein Nachteil:Im Laufe von vielen Jahren (>15) wurde meine erste Dose von innen her undicht, und der Inhalt verteiltesich immer mehr im Aufbewahrungskarton. Die Dose rostete von innen her durch. Wahrscheinlich haben diez.T. aggressiven Inhaltsstoffe das Metall zum korrodieren gebracht."What about "Oszillin T6" ?http://teslanol.ch/teslanol-produkte-uebersicht.html?id=5https://www.elv.de/teslanol-kontakt-tuner-spray-200-ml.html

author: Vgkid
author_rank: Super Contributor
timestamp: March 28, 2017, 08:46:48 pm
content: What is the decade(model/manufacturer)Post pics of the switches. That will help in the determination of the course of action.

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 28, 2017, 08:51:20 pm
content: It's a Burster 1422:I can post photos of the switches tomorrow.

author: babysitter
author_rank: Frequent Contributor
timestamp: March 28, 2017, 10:02:23 pm
content: Hier als Datenpunkt: Ein zufriedener Nutzer von Teslanol Oszillin. Solltest Du im RheinMainGebiet sitzen kannst Du dir einen oder Spritzer abholen ohne ganze Flasche zu kaufen!BTW: Das Kontakt 60 kann man zum _reinigen_ verwenden, wenn man es hinterher gut auswäscht.

author: Vgkid
author_rank: Super Contributor
timestamp: March 29, 2017, 07:00:22 am
content: Quote from: carl_lab on March 28, 2017, 08:51:20 pmI look forward to it. Burster makes some high quality resistors.

author: BU508A
author_rank: Super Contributor
timestamp: March 29, 2017, 10:01:50 am
content: Here you can find a .pdf of the Burster 1422:http://www.physicomcorp.com/doc_series/1422_Ser_Ovr.pdfNice gear, btw.

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 29, 2017, 10:07:53 am
content: New photos...

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 29, 2017, 10:09:00 am
content: .

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 29, 2017, 10:23:45 am
content: ..

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 29, 2017, 10:24:57 am
content: ...

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 29, 2017, 11:43:10 am
content: Quote from: BU508A on March 29, 2017, 10:01:50 amThank you!Quote from: babysitter on March 28, 2017, 10:02:23 pmYou have mail! (PM)

author: Kjelt
author_rank: Super Contributor
timestamp: March 29, 2017, 03:34:40 pm
content: Quote from: carl_lab on March 28, 2017, 08:01:14 pmJust checked andDarn I bought this can I think two or three years ago, what a mess.But indeed it needs to be washed with WL that is standard practice.BTW: I got the same problem two years ago with a can of videohead cleaner, but that took ten years to rost through and is not corrosive at all.Any bit of moisture inside can start the process.

author: Kjelt
author_rank: Super Contributor
timestamp: March 29, 2017, 03:46:49 pm
content: It even gets weirder, just cleaned my drawer and when placing back the Kontakt 61 and Kontakt WL they felt empty and they are empty.Never used in three years and then poof gone with the wind. Unbelievable.My Kontakt Dustoff, PCC and IPA are ok though.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 29, 2017, 04:51:16 pm
content: Hi,Years ago, I also cleaned a Burster resistance box, same problem, first with Q-Tips and alcohol, but that was not enough, so I did it mechanically, using fine polishing emulsion I use for our CERAN cooking field.Take a bit of this emulsion on a Q-Tip, and polish the contacts until the copper contacts look bright again. The Q-Tip will get really black.Afterwards, wipe the emulsion off with another Q-Tip.This procedure lasts for many years already, zero resistance is still about < 20mOhm.I can confirm the rusty Kontakt-60 can-I'll never use that stuff again.Frank

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 29, 2017, 06:43:04 pm
content: Hi Frank!Quote from: Dr. Frank on March 29, 2017, 04:51:16 pmAre you sure, that were copper contacts?The 1422 contacts looks more like gold or silver plated to my eyes...Maybe your decade is 1406 or 1407 (7-digits)?You had the problem in "0-position" or in "10-position"?I think "0" and "10" are prone to contact problems, because there is no possible "mechanical overshoot" when dialing these positions (the mechanical end stops are very tight tolerated).If I wiggle the dial very little bit back and forth (barely noticeable), contact resistance becomes immediately good.Quote from: Dr. Frank on March 29, 2017, 04:51:16 pmThat's not enough for the 1422 spec. (5 mOhm for each 3-digit "half").My decade is in spec. regarding "zero". Only problem is the 10x1 Ohm position.Quote from: Dr. Frank on March 29, 2017, 04:51:16 pmDéjà-vu...I also never used Kontact-60 again, and if I used Kontakt-61 I double checked it is not K-60 (with a bad feeling in my stomach remaining).

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 29, 2017, 08:52:53 pm
content: Quote from: carl_lab on March 29, 2017, 06:43:04 pmYou're right, it's an old 4107, similar to 1407.It should be < 10mOhm, and has about 13mOhm at the moment. (added:9.6 mOhm with 4W and OCOMP)I'd guess, that after 40 years, the spring force of the wiper contacts have decreased a bit.Maybe, that's the problem with your 1Ohm decade.For determining the contact material I had to open my unit, see picture.It's hard to tell, what Burster has used.It's definitely no pure copper, but I also doubt that it's gold plated, as these strong spring contacts would easily rip that off.Also, gold plated contacts would be easy to clean with alcohol, as gold does not oxidize.Seems to be something like a brass alloy, or phosphorous bronze.I remember, that most of these contacts had been looking really black, and the self-cleaning mechanism, as advertised by Burster, did not do the job any more.So I had to do this mechanical polishing.FrankPS: does yours really have these stepper motors inside, with IEEE488 interface?Would like to see and hear this resistor box in action..

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 29, 2017, 09:16:04 pm
content: No, it's not the motorized option.Thanks for posting the photo of your switches.Yes, determining contact material by appearance is very difficult. The color of your contacts looks very similar to mine, see my first 3 photos. (My last 3 microscope photos were highly colour degraded because of poor white balance or wrong camera colour profile - I had to use that unfamiliar microscope of our neighbour department...)Have you relubricated contacts after polishing?What do you think about the "mechanical overshoot" point?I'm not sure if I could make clear enough what I meant by "mechanical overshoot"...

author: Vgkid
author_rank: Super Contributor
timestamp: March 29, 2017, 11:31:15 pm
content: Those switches look rather nice. If chemical means dont work, go with some fine sandpaper/emory cloth. I actually prefer that one.

author: carl_lab
author_rank: Frequent Contributor
timestamp: March 31, 2017, 08:13:04 am
content: I ordered "Oszillin T6", again.I hope Buerklin can deliver this time...

author: Kjelt
author_rank: Super Contributor
timestamp: March 31, 2017, 01:26:26 pm
content: No sandpaper that is too coarse, use normal printing paper, takes a bit more time but it is just as effective but does not take off the plating.

author: Smith
author_rank: Frequent Contributor
timestamp: April 01, 2017, 06:16:03 pm
content: I normally use Kontakt 60 for cleaning really dirty contacts, then clean/rinse very well with IPA and cotton sticks. Normally fudging some white paper soaked in IPA between the contacts works well enough. For bigger contacts I even use wet grid 2000 sandpaper or metal polish (and clean with IPA afterwards).I have used Kontakt 61 (for protecting instead of cleaning contacts) on some heavily corroded but cleaned contacts. It still seems to work well, much better than without the Kontakt 61.

author: Krampmeier
author_rank: Regular Contributor
timestamp: April 01, 2017, 08:42:18 pm
content: I have a similar resistor decade, but with 4 digits only. Very nice ww manganin resistors inside, got it for just 15 euros at a ham radio flea market...The unit had unstable connections at all the contacts, and cleaning did not help, so I took the thing apart and bent the spring contacts a bit to increase the pressure. That solved the problem and the decade is still very close to it's spec.As this method was not suggested yet, I wonder if bending the contacts (possibly made of beryllium copper alloy) by hand is something so terribly bad that no one should ever even just consider it? Will it harm the contacts on the long run?I attached two photos of the box, unfortunately I did not take any pics of the contacts...By the way, those Burster decades are really nice. They sometimes drift and go out of spec after 30 years or so, but usually they are very reliable. There are lots of them at my workplace, including some with motor and GPIB connection. They are annoyingly loud when changing the value though. Unfortunately, Burster does not have any spare parts for the motors any more, so if one of those fails, you have a big problem...

author: babysitter
author_rank: Frequent Contributor
timestamp: April 01, 2017, 09:09:24 pm
content: My father who was caring for and feeding thousands of relay contacts (post office) had wooden sticks with paper and/or leather on the end in his workbox, I have to ask him if they were used immediately on the contacts.

author: Smith
author_rank: Frequent Contributor
timestamp: April 02, 2017, 05:44:47 am
content: Quote from: Krampmeier on April 01, 2017, 08:42:18 pmI would only use this as a last resort. I have seen people use this method for bad contacts, but you are possibly creating a weakspot in the metal you are bending. Depending on how much the spring contact is moving and its thickness, the problem can come back quite soon. Of course, the second time you bend it, it gets worse and worse.Bending contacts to overcome dirty connections can also wear out the connections prematurely due to the connections scraping eachother with more force. I have seen this happen a few times.

author: SeanB
author_rank: Super Contributor
timestamp: April 02, 2017, 08:34:13 am
content: Quote from: babysitter on April 01, 2017, 09:09:24 pmYes, those were used to burnish contacts. the leather strips were dipped in a little alcohol and rubbed on the german silver contacts to clean them, and the paper ends are used with the relay contacts held closed to burnish the mating surfaces to a even fit. The leather was reusable, and the paper could be cleaned a few times in alcohol before you tossed the stick out. The paper used is a very high clay art paper, and the clay is the abrasive material there.You can also use some plain high clay art paper ( at the craft store, used for watercolours as it does not wrinkle) cut into strips to burnish the contact surfaces, simply cut into strips and draw between the contacts a few times, and toss after each contact.