Function Test of ISKRA 111M Soviet Nixie Calculator

After repairing the power supply, I noticed that only the number 7 worked. Upon closer inspection of the keyboard(it uses reed switches and magnets), 7 was actually inverted. This meant that when the key was pressed, the switch would open, but otherwise would be locking the machine into a state where it wasn’t accepting other inputs.

To fix this, I simply flipped around the magnet in the key slider and it solved the issue. Surprisingly there isn’t a single fault in the 40 year old -27V MOS logic ICs, for now at least.