Take a look at this Impedance selector switch. Not sure what to make of these terminals?

[SoulFetish]

Not sure if I've ever seen one in this condition?? This is labeled as NKK, which makes high quality switches, but I've never seen any of their switch terminals suffer this kind of blueing before. I'm wondering if this might not be a counterfeit production.



What do you guys make of this?

[Mick Bailey]

It looks like silver sulphide, which initially forms a yellow and blue rainbow-type discoloration and then eventually turns black. Note that the areas around the solder joins are protected with flux residue. It often forms as a result of atmospheric contamination.

[Justin Thomas]

I've seen similar things happen when I accidentally leave my iron on too high. Doesn't happen on everything, but sometimes... Especially with those block-shaped red plastic speaker jacks with wide terminals & other things with tabs like that.

Justin

[Mick Bailey]

If you have some household ammonia you can dilute it a little and use a q-tip to see if it removes the discolouration. If it does I'll bet the contacts are silver plated.

[SoulFetish]

If you have some household ammonia you can dilute it a little and use a q-tip to see if it removes the discolouration. If it does I'll bet the contacts are silver plated.

I just checked the datasheet for the HS series switches and they do have some models with silver plating.
I've just been reading up on silver sulphide, silver plated contacts, and problems leading to contact failure. Pretty interesting paper here, and a quick read:
2002 technical paper - Silver Corrosion

If this is corrosion of the silver plating on this switch, It makes me question the wisdom of using untreated silver plating on exposed/open switch contacts.
I used to work for a jewelry manufacturer, and they would use Rhodium Plating to maintain the silver finish and prevent tarnishing.

[Leo_Gnardo]

The wiping action as you work the switch scrapes off the soft corrosion layer, as you can see in the photo. And if you're worried, apply a tiny dab of DeOxit to the terminals. Those switches if I'm not mistaken are rated for some enormous current, something like 30 amps. The most they'll see in any tube application might be around 1/3 of that, in a 300W amp running a 2 ohm load, half that for most any more common amp/load combination

[Chuck H]

This^^^^^^^^^^^^^^^^

A little reading on line indicates that silver plated contacts aren't ideal for low voltage applications. And this would be a low voltage application. I think, clean them and apply one of the tacky/viscous type contact treatments. I don't even know who makes stuff like that, but I've seen it on many switches I've serviced. The DeOxit product Leo mentioned may be one of them. I've never bought the stuff.

[Leo_Gnardo]

The DeOxit product Leo mentioned may be one of them. I've never bought the stuff.

DeOxit is typically supplied as a 5% spray, the remainder being mostly naptha which is a darn good cleaning solvent. IF the DeOxit formula is still the same as Cramolin, its predecessor (available since 1928 !) , the old advice was "the less you use the better it works." So having a glob of DeOxit or Cramolin on the contact works against you, can bring on more corrosion & make for a lousy contact. When the stuff was gaining popularity in the hi fi world, late 1970's, some people overdid it, gooping up their tube contacts & everything else in sight. More is better, right? Not in this case. Just a couple of molecules is plenty enough apparently. Apply a dab with a Q-Tip, toothpick or something like that, give it a few minutes to do its thing, wipe off the remainder, maybe with some solvent. What little remains is enough to maintain a good contact.

FWIW Caig has a paste formula intended for high current applications. I let my brother know this - he works for Teledyne Continental - manufacturer of piston airplane engines. I think they now use the stuff in their magnetos. And Caig boasts lots of other hi tech manufacturers & organizations in their list of satisfied customers. Like NASA and Boeing. (No, DeOxit didn't figure into the demise of those dodgy 737's.)

[Chuck H]

So what IS that transparent amber, tacky stuff that I find on old switches and sometimes even jacks or pots? Which, BTW, are rarely oxidized where that stuff is still present.

[Leo_Gnardo]

So what IS that transparent amber, tacky stuff that I find on old switches and sometimes even jacks or pots? Which, BTW, are rarely oxidized where that stuff is still present.

Yes I've seen that too. I suspect it's just regular old grease that's oxidized with age. I find it in various bits of cars I've worked on too, most have nothing electrical about them. In old turntables too.

Heck I just washed up an old Revere ware pan that's hanging on my kitchen wall, haven't used it since Esther was a pup. Plenty of sticky grease & bits of fiber stuck to that ol' relic, just from exposure to the typical kitchen atmosphere contaminants. Crap, I'm gonna have to get a new dish scour/sponge now, that mess gummed the old one up badly. No matter, it's about time anyway.

[Chuck H]

Yes I've seen that too. I suspect it's just regular old grease that's oxidized with age. I find it in various bits of cars I've worked on too, most have nothing electrical about them. In old turntables too.

Heck I just washed up an old Revere ware pan that's hanging on my kitchen wall, haven't used it since Esther was a pup. Plenty of sticky grease & bits of fiber stuck to that ol' relic, just from exposure to the typical kitchen atmosphere contaminants. Crap, I'm gonna have to get a new dish scour/sponge now, that mess gummed the old one up badly. No matter, it's about time anyway.

Ok. I can buy that, but the stuff I'm speaking of seemed to me more often exclusive to contacts, evenly distributed (never globy) and always has the same smell and color.?. Also, I know that grease and anything viscous can gather dust and crap that can foul switches, but this stuff never looks dirty. Maybe it's just old grease, but if so they should come up with a way to make something like it for application on contacts

[Helmholtz]

There is certainly something like contact grease. E.g.: https://www.amazon.com/LubriMatic-11.../dp/B001446LP4

The grease found inside pots is typically for lubrication and friction control of the shaft. It is not meant to be on the carbon track.

[Chuck H]

There is certainly something like contact grease. E.g.: https://www.amazon.com/LubriMatic-11.../dp/B001446LP4

I know THAT stuff. Could work I think. My consideration is that those contacts could be cleaned and then something applied that will stay put to keep them from further oxidation.

BTW, don't get any of that stuff on your hands or you won't be able to pick up or hold on to anything for a day or two!

[Helmholtz]

BTW, don't get any of that stuff on your hands or you won't be able to pick up or hold on to anything for a day or two!

Means that it probably contains silicone grease, which doesn't easily wash off with soap.

Often Vaseline (petroleum jelly) is used on contacts. But there are more specialized products sold e.g. by ElectroLube.

But any contact lubrication on moving contacts will reduce the self-cleaning effect described by Leo, so I'm not sure if it's always a good idea.

[Mick Bailey]

I don't like silicone grease near contacts. It migrates, causes problems with resoldering and can prevent non-wiping contacts (such as found in rocker switches) from making contact. I prefer RS components contact grease for some contact types, but only where necessary. Kontakt Chemie 60 is really good for removing silver sulphide and leaves a protective film.

The grease in pots is sold under the brand Rocol Kilopoise. As a good substitute use PJ1 chain lube - spray it into a small container and let the solvent evaporate. I use this a lot when rebuilding pots and want something a little more gap filling than kilopoise.