Soemtron Downloads

Soemtron logo of unknown origin

As we accumulate drawings and other information for the Soemtron ETR 22x range of calculators we are making that information available here, but please note that this information is provided in good faith and will undoubtedly contain errors given the age and nature of the subject.  Updates and corrections to the drawings are uploaded on an ad-hoc basis as we work on our current collection of Soemtron ETR 220, ETR 222 and ETR 224 machines and receive information from contributors.  We do not accept responsibility for their subsequent use.  The files will usually be in pdf format so a current copy of an Adobe Acrobat[1] reader will be needed to view them.  To download the files right click the relevant link and select "file save as ....".  All files on this website are ©2007- and its group websites[2] or the files respective owner.

Our circuit diagrams (schaltplan) are reverse engineered from our collection of Soemtron ETR calculators, some of which are in the process of being refurbished, hopefully to full working order.  Our circuits are drawn on Pads Powerlogic 5.0 or AutoCad LT and we claim copyright on these drawings only.  We freely acknowledge that the original intellectual property rights of the Soemtron ETR series calculators resides with V.E.B.[3] Büromaschinenwerk[4] Sömmerda and their designers.

When referencing the drawings we have followed the original component idents as found on the boards, however to better fit with the schematic drawing package we are using, component references for the circuits are prefixed by the board number or ancillary function. EG. for Board 7 resistor R24 the reference is "7W24" (resistors are Widerstand in German), "KW2" is resistor R2 on the Keyboard.  Missing or left over components are left on each circuit diagram until any potential problems with those components have been resolved.

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If you have any further historical information, circuits, drawings, photographs, data or manuals about the Soemtron ETR 220, 221, 222, 224 or their manufacture, test equipment (Prüfgeräte) or you just know more about the Soemtron companies in general then please let us know, contact us.

In reverse engineering our Soemtron's we have been very fortunate to have managed to obtain a copy of a few of the original German and Russian diagrams for the Soemtron 220, the following list is a translation of the German component references and terms that we have found so far, that were used on some of these drawings.

Component / TermReferenceTranslation
Flip Flop Bistabile Kippstufe
Carry Übertragung (UBER)
Write Schrieb
Quality standard1 - 3Güteklasse
Many thanks to Philipp Maier for the above translations.
Ferrite core driver Ferritekerntreiber
Measure or TestpointMPMessPunt
Read Lesen / LES
Read amplifier Wiedergabe verstarker
Write Schreib
Many thanks to Bernard Green for the above translations.

Datasheets for some of the components used in the Soemtron 220
2SB75Transistor 2SB77Transistor
Z570MNixie tube KY130Silicon diode
1N35 (GAZ17)Germanium diode GAZ17Germanium diode
GS121Germanium transistor   

Downloads -
Part number list - a list of all Soemtron part numbers currently available to us from various documents (35Kb)

1 Download Adobe Acrobat Adobe reader download. [top]
2 Group websites [back] [top]
3 Wikipedia entry for V.E.B. = Volks Eigener Betrieb, or Peoples Owned Company V.E.B. [back] [top]
4 Büromaschinenwerk. Office Machine Works. [back] [top]

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