Servicing decade resistor

[NWerner]

Hello,

I recently acquired an oldish genrad 1652-A. I plan to implement null-detector and excitation voltage supply to resurrect this instrument with a more modern interior.
I mainly care for the decade resistors and have no interest in those unobtanium tubes and passives.

during closer inspection two question arose:

a) there is some corrosion on the 0.1R step contact lever. What do you advise me to do on this?
b) Imprudently I cleaned away some grease which was aplllied at the contacts. What can be used to protect those contacts from corrosion?

As far as I know/read/guess/see:

- switches have a contact resistance of <1mR
- contact pads are pure copper without plating
- contact levers consists of four seperate levers with shiny surface (silver?)
- resistors are manganin
- no special precautions regarding EMF are implemented


Best Regards
Norman

[dacman]

I suppose you mean the green corrosion (which is common).  Try a nylon bristle brush or if you're careful you could use a steel brush.  I would then lubricate it with your favorite contact lubricator (even on non-contact surfaces).

To protect the contacts, you could lubricate them or use carbon conductive grease.  Something else I've used is DeoxIT L260.

[Conrad Hoffman]

I'd lube the contacts with a bit of Vasoline or some Superlube PTFE grease. I'm a big fan of old GR stuff, but the resistance limit bridge was one of the few GR things I found completely worthless in the modern world. IMHO, anything you can do to make it serve some useful purpose is fair game. BTW, yours seems to have better resistors and switches than mine did.

[Neomys Sapiens]

If nylon brush or similar doesn't work, I recommend using a glass fibre contact cleaner. Also known as glass fibre eraser.
For example:
https://www.ebay.de/itm/ECOBRA-Glashaar-Kontaktreiniger-GLASFASER-PINSEL-Fiberpen-Glasradierer/322496656517?epid=10011032220&hash=item4b164c7485:g:PyoAAOSwZ~tbm-xu:rk:33:pf:0

[NWerner]

Thanks for your tips and advise - Hopefully I will find some time over the holidays to play with my new toy.

[001]

Why do You reccomend agressive chemical sprays?
Pure coper contacts oxidised so easy
Is some oil like vaseline will be best protection from AIR?

[rbm]

The best cleaner for these contacts would be Deoxit. It's a spray contact cleaner that is formulated to clean oxidation off of the exposed copper-berillium contacts and leave behind a conductive chemical that inhibits further oxidation.

[babysitter]

Well, is there a source of DeoxIT in germany?

Dont ever use Kontakt 60 alone, it will clean but keep on cleaning. The rust you sometimes see on Kontakt 60 cans is a tell-tale sign.
KONTAKT wants you to use 60 for solving crud, WL for washing off crud and 61 for conservation.
For myself, I consider Teslanol T6 and Ballistol suitable.

EDIT: Glass hair is something I use to remove solder stop or other covers, would never use it on contacts. Mohs-Härte 5,5. There are just a few electronics' metals above that.

[rbm]

Well, is there a source of DeoxIT in germany?

Amazon.de for one.  It should also be available at high end audio stores.

[MarkF]

Any chance you can crop those pictures.....

   Why upload huge pictures that are 90% white?

[Gyro]

Electrolube EML is excellent and easy to find. Similar properties to Deoxit, just less hyped.

https://www.electrolube.com/products/contact-lubricants/eml/contact_cleaner_lubricants/


P.S. They used to sell it in a handy pen applicator. These days it's better to spray into a container and use a cocktail stick to apply.