Burster digistant 6425 T (current source) teardown and repair.

[The Soulman]

This little current source has been acting up for some time, occasionally it would produce lower current with tremendous amounts of noise, a little mechanical persuasion would usually fix it but now I have enough of it and had a proper look at it.
From the outside I could narrow it down to the external/internal v-ref switch on the back.
After opening up the digistant I spotted the culprit, can you?
It have been like this for forty years. 

Apart from the defect and one of the resistors on the second decade being out of spec, it is a handy little thing.

Pics attached for your entertainment. 

[The Soulman]

Some more info:

Output range: 0,001 mA to 110mA (first dial goes up to ten, others up to nine)
Maximum output voltage: 20 V
Maximum error: 0,03%

Op-amps: 3) ua741, 1) LH0042
Zener: unknown
Precision resistors: Burster in various grades

[Dr. Frank]

  thank you for these pictures!
Always loved Burster resistors, built many CC sources out of them...

That lead coming from the switch, left under that 100M resistor did never see a solder joint, for as much as 42 years, obviously.

Frank

[Vgkid]

Thanks for the teardown. It is always interesting to see inside various precision current sources. They are always aimple.
Did you find a schematic for it.

[The Soulman]

One of these days it is coming apart again, the rear switch is still a bit dickey, anyone want
some pics of anything specific?