This has been a major restoration project in my lab for the last year - and now that I got the whole "cage" a.k.a. arithmetic logic unit, I could finally get the thing working. I learned a lot of stuff on diode & transistor logic, ferrite core memory, digital electronics in general...

It's technically made in the 1960s/70s (1966-1977), so Apollo time... all this while my side of the world ran on discrete germanium transistors and ferrite core memories.

Visit the excellent https://soemtron.org/ for tons of schematics and other info! Mike Hatch is a brilliant guy to have gathered and shared all the knowledge he could find in Sömmerda.

0:00 Intro 1:15 Operating the Soemtron... and Story Time! 11:40 What's Inside 13:55 The Arithmetic Logic Unit (ALU) 14:15 Ah, The Memories! 16:10 Ferrite Core Memory Addressing Control Board 19:30 My Soemtron Repair Story 23:30 Voltage Levels and Diode/Transistor Logic Explained 23:50 Flip Flop and Differentiating Circuit Explained 28:35 Ferrite Core Memory Construction and Organization 33:20 Ferrite Core Memory Operation Explained 37:00 Memory Addressing in Soemtron 41:20 On Eastern Bloc Electronic Engineering... and Nixie Multiplexing Control 46:08 For Die Cast Alumin(i)um Afficionados 47:00 Lifting the Front Cover 48:15 VEB Büromaschinenwerk Sömmerda - East German IBM? 49:15 Nixies and Lightbulbs 50:20 Decimal Point Selection Switch and Keyboard 52:40 Recombobulation 53:55 Mains Switch 57:20 Mains Plug 58:06 Afterword... And Some More Soemtron Insights!

For some additional tech info, check out my scribbling at https://hackaday.io/project/188565-soemtron-etr220-restoration-project

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