Hi Frank!
Are 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 machanical end stops are very tight tolerated).
If I wiggle the dial very little bit back and forth (barely noticeable), contact resistance becomes immediately good.
That'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.
You'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.
Frank
PS: does yours really have these stepper motors inside, with IEEE488 interface?
Would like to see and hear this resistor box in action..