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Soemtron Downloads

As we accumulate drawings and information for the Soemtron calculators we are making that information available here, but please note that this information is provided in good faith and will undoubtedly contain errors. Updates and corrections to the drawings as we work on our current Soemtron ETR 220 project are uploaded on an ad-hoc basis as they are finished. We do not accept responsibility for their use. The files will usually be in pdf format so you will need a current copy of an Adobe Acrobat reader which you can get from here. To download the files right click the relevant link and select "file save as ....", to view the file directly just click the link assuming you have a pdf viewer installed !. All files on this page are (C)2007 somtron.org, all other files and pictures on this site are copyrighted to their respective owners.

All circuit diagrams are reverse engineered from a Soemtron ETR 220 that we own and are in the process of re-conditioning, hopefully to full working order. The circuits are drawn on Pads Powerlogic 5.0 and we claim copyright on these drawings only. We freely acknowledge the intellectual property rights of the Soemtron ETR series calculators resides with V.E.B. Büromaschinenwerk Sömmerda (1) and their designers. The following list is a translation of the German component references and terms used that we have found so far.

Component / Term	Reference	Translation
Resistor	W	Widerstand
Diode	GR	GleichRichter
Flip Flop		Bistabile Kippstufe
Carry		Ubertrag (UBER)
Write		Schrieb
Quality standard	1 - 3	Güteklasse
Many thanks to Philipp Maier for the above translations.
Ferrite core driver		Ferritekerntreiber
Measure or Testpoint	MP	MessPunt
Read		Lesen / LES
Read amplifier		Wiedergabe verstarker
Write		Schreib
Many thanks to Bernard Green for the above translations.

When referencing the drawings we have followed the original component idents as found on the boards. Component references for the circuits are prefixed by the board number or ancillary function, EG. for Board 7 Resistor 24 the reference is "7W24", "KW2" is resistor R2 on the Keyboard (resistors are Widerstand in German). Missing or left over components are left on each circuit diagram until the problem with those components have been resolved.

If you have any information, circuits, drawings, data or manuals about the Soemtron ETR 220, 222, 224 or their manufacture please contact us here

Circuit and Logic diagrams -
(See the "Snagging list" file for the current list of things to check on the circuits drawn so far)

1	Keyboard	Keyboard circuit	updated	26/6/2008
2	Display	Display circuit	updated	26/6/2008
3	Backplane	Backplane circuit	updated	26/6/2008
4	Board 12 Board 12	Cathode drivers and numeric key encoding circuit Logic diagram	updated	15/7/2008 15/7/2008
5	Board 11 Board 11	Anode drivers and function key encoding circuit Logic diagram	updated updated	10/7/2008 15/7/2008
6	Board 10	5 bit display "Z" counter circuit	updated	26/6/2008
7	Board 9	F2,5-6 function latched circuits, including register addressing	updated	30/6/2008
8	Board 8	F1/3, VER and MZ function latched circuits	updated	26/6/2008
9	Board 7	B1-4, VOR and R function latches circuit	updated	26/6/2008
10	Board 6	Control gating circuit	updated	26/6/2008
11	Board 5	V, SCHRIEB, S1 function latches and 25Khz clock circuits	updated	26/6/2008
12	Board 4	Arithmetic unit E Register (input), Carry latch and digit drives 0/1 circuits	updated	9/7/2008
13	Board 3	Arithmetic unit A Register (output) and digit drives 5-9 circuits	updated	26/6/2008
14	Board 2	Core memory drivers and decoding circuits	updated	9/7/2008
15	Board 1	Core store, read amplifiers and digit drives 2-4 circuits	updated	26/6/2008
16	Supply	Power supply circuit	To be designed


Complete circuit	All current circuits for the Soemtron 220 (4.88Mb file)	updated	15/7/2008
Complete logic	All current logic diagrams for the Soemtron 220 (357Kb file)	updated	15/7/2008
220 net list	Net list for the Soemtron 220 circuits	updated	15/7/2008
Snagging list	Current problems with the circuits for the Soemtron 220	updated	10/7/2008

Datasheets for some of the components used in the Soemtron 220
2SB75	Transistor datasheet
2SB77	Transistor datasheet
Z560M	Nixie tube datasheet
KY130	Silicon Diode
1N35 (GAZ17)	Silicon Diode


Russian Technical Manual for the Soemtron 220
These manuals are courtesy of Gerhard Just, including a basic description of the logic elements, their component values, operation and even a timing diagram or two.
Technical manual - 10Mb pdf	Logic diagram - 1.4Mb pdf

German Logic diagrams for the Soemtron 220
These drawings are courtesy of Bernard Green, they include component references and values, logic symbols and a diagram for each board. They give an insight into the what the logic designers were able to achieve in the functions of the Soemtron ETR 220 with such basic, albeit almost primitive electronics then available in 1960's German Democratic Republic.
Gates	AND - OR Gates
Buffers - 1	Buffers
Buffers - 2	More buffers
Delays & FlipFlop inputs	Delays & FlipFlop inputs
Basic FlipFlops	Basic FlipFlops
Monostables	Monostables
Schmitt Trigger	Schmitt Trigger
Clock oscillator	Clock oscillator
Core driver	Core driver
Core sense amplifier	Core sense amplifier
Nixie tube drivers	Nixie tube drivers
Power supply	Power supply

And the boards -
Board 12	Cathode drivers and number key encoding
Board 11	Anode drivers, digit position decoder function keys encoding
Board 10	Display digit position counter
Board 9	Memory Register addressing
Board 8	Negative result latch plus three other undefined
Board 7	Function latches
Board 6	Control gating
Board 5	Function to be determined, Clock oscillator
Board 4	"E" register, misc gating and drivers.
Board 3	"C" register
Board 2	Core Memory Read, Write and Inhibit drivers
Board 1	Core Memory and datasense amplifiers

V.E.B. = Volks Eigener Betrieb, or Peoples Owned Company. back
Büromaschinenwerk = Office Machine Works. back