Iskra Unimer 3 - repair and mod for external power

[Thilo78]

Hey guys,
I finally came around to open up the Unimer 3, that I inherited from my father.

It featured several problems:
- Corroded battery contacts due to leaky batteries
- Corroded fuse holder
- Wrong and/or slow readings

Repairing it was a bit problematic due to lack of documentation. The only thing I found was a schematic diagram.
No markings on the board whatsoever, but at least a few pieces of information on the components themselves.
After quite a bit of measuring I put together a map of the components. Might prove itself useful to others trying to revive an Iskra.

The actual problem came from a lifted trace in the positive path to the movement. I repaired that with a piece of tinned copper wire.

I replaced the fuse holders with new ones, but couldn't get new battery terminals. So I opted for external power supply.
On top of the case, I positioned two 2mm jacks and wired them to the battery connections.
Thus, I can plug in a battery pack if I need to do resistance measurements, and don't need to worry about leaky batteries.

[Thilo78]

btw: One of the pictures shows the Unimer 3 next to my Goerz Unigor A43.
They really look alike, but the Unimer is a bit smaller.