Gallery
ETR 220
ETR 221
ETR 222
ETR 224

Soemtron Calculators Gallery

The Soemtron 220 ........
Many thousands of Soemtron ETR 220's were made during their production run and by modern standards they are large and cumbersome, but very typical of their age - the 1960's. This section shows a few views of a typical Soemtron ETR 220 in good condition owned by calculator collector Serge Devidts. Manufactured from 1966 to 1977 by V.E.B. Büromaschinenwerk Sömmerda, 155,142 Soemtron ETR 220 desktop calculators were built during the eleven year production run. Click any image for a larger version.
	Inside view	Decimal point selection	Nixie tube display close up
Pictures ©2007 Serge Devidts, used with permission, for more see his site here.

The Soemtron 221 ........
Following a chance comment by Bernard Green, about a possible ETR 221 unit, an email from Serge Devidts has confirmed the existence at some time in the past of a two part ETR 221. Bernard had suggested the existence of just such a machine, having recently said that he recollected seeing a two part unit shipped into the UK whilst he was working at Office and Electronic Machines in London. The 221 is a printing version of the 220, but split into two parts: a desktop unit with keyboard and printer mechanism, and an ancillary unit (floor or desktop ?) with the main electronics (and power supply ?). So far only one of these units is known to have existed, that unit shipped to the British importer of Soemtron calculators - Office and Electronic Machines - in London.
Early model ETR 221		Picture ©2009 Serge Devidts, used with permission, for more see his site here.Click any image for a larger version.

The Soemtron 222 ........
Manufactured from 1970 to 1972 by V.E.B. Büromaschinenwerk Sömmerda, 3,203 Soemtron ETR 222's were built during the two year production run. The processing logic of the Soemtron ETR 222 calculator, derived from the ETR 220, is all transistorised.
	Inside view	Pictures ©2007 Ruediger Kurth (Robotron) Used with permission.Click any image for a larger version.

The Soemtron 224 ........
With just over 526 machines built in a six year period, again by V.E.B. Büromaschinenwerk Sömmerda, the ETR 224 is now a very, very rare machine. Only four are known to exist, one in the museum in Sömmerda, one in a private collection also in Sömmerda, one in our collection and one in a museum in Naunhof. The processing logic of the ETR 224 is believed to be derived from the 222. Click any image for a larger version.
	Pictures ©2009 Ruediger Kurth (Robotron), Used with permission. and ©2009 www.soemtron.org	Inside view

Various photos of our Soemtron 224 before restoration
Photos of the restoration progress.

The Extender Card ........
Test equipment for the Soemtron machines is very unlikely to be found, indeed in discussions with engineers from the old Soemtron factory on a recent trip to Sömmerda it transpires that the factory and contents are long gone. To this end we are designing our own test equipment, and the most useful at the moment is this extender card. Click any image for a larger version.
Extender board	Extender board socket	Extended board	Board and extender

Soemtron 220 production ........

Two photos here show a Soemtron 220 production line from the book "BWS Sömmerda", by Annegret Schüle, (ISBN 39-8039-311-9, or ISBN 978-39-8039-311-9) published by Desotron Erfurt in 1995. Dr. Günter Hartmann of DESOTRON has kindly given us permission to use these images from the book.

The two photos (left) below show a ETR 220 production line, with the left side of the production line appearing to be operators checking each machine, whilst the right side appears to be a row of technical checkout or diagnostic stations. Each station has an oscilloscope and a "Prüfgeräte" or test box beside it to aid in de-bugging. Listed in the Russian technical manual as a "display panel of an electronic invoice machine « Soemtron-381 » of type 8601", the Soemtron Prüfgeräte was a custom designed piece of test equipment that plugs into a pair of diagnostic connectors inside the machine. All three models of the ETR range have these test connectors, and we suspect that there were separate panel overlays for the test box to show the differing flip-flop arrangements between the models - especially as the manual instructs "4) Fit the display legend to the indicator panel (Fig. 32)). (Click here for a table of the service connector differences). An ETR 220 panel layout can be seen on page 185 in the Russian Technical Manual on the "Downloads" page. Interestingly each ETR undergoing test appears to be in a master carrier frame, it's not known at this time if this was just to assist in moving the units around or if they were actually used for electrical connections in the test process.

The third photo (right) is of a couple of prototyping boards, the topmost one being for the ETR 22x series calculators and other machines that Soemtron produced using the same PCB form factor. These prototyping boards appear to be the more usual fibreglass construction, however it would appear that all of the boards manufactured for the Soemtron ETR 22x range of machines were of the brown phenolic paper based construction. We presume this was for cost considerations, but it also could have been the availability of fiberglass materials and resins in the GDR at the time.
Click any image for a larger version.

Soemtron 220 production

Pictures (left) ©1995 DESOTRON
www.desotron.de
Used with permission.

Prototype boards

1	ETR 220 production of 155,142 during 1966-1977	Page 389 "BWS Sömmerda", by Annegret Schüle ISBN 39-8039-311-9, ©1995 Desotron Erfurt.
2	ETR 222 production of 3,203 during 1970-1972	As above
3	ETR 224 production of 526 during 1968-1974	As above	back

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