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Soemtron ETR 220
Coming soon to a website near you - the Soemtron ETR 220.
We have the technology, we can rebuild her !
This website is dedicated (in probably a very nerdy way !), to parts of what turned out to be a Soemtron ETR 220 calculator purchased during 2007 from a company in Prague, the capital of the Czech Republic, after a Google search for "core memory" during some research into the PDP7 range of computers manufactured by the now defunct Digital Equipment Corporation. The equipment duly arrived, but it was found to be in a very poor state (see the top picture), dirty, rusty and missing its power supply and top covers. After a few days research and translating some German text off of the baseplate, it turned out to be a Soemtron ETR 220 calculator, a very interesting piece of early electronic calculator history originating from 1960's and 70's German Democratic Republic.
 A typical Soemtron ETR 220 |
Over time we will repair, conserve and hopefully get into working order this interesting piece of Eastern Bloc calculator history from the 1960's. Bookmark this page and come back from time to time for a visit and see how we are getting on. In the end we will publish a full circuit diagram of the machine and its inner workings for those of you who are interested - not many probably !, but there again this is the Internet, see you again soon.
The second picture is of a good condition Soemtron ETR 220 owned by calculator collector Serge Devidts, for more see his site here
Timeline -
Older news from soemtron.org can be found here.
August 2008 -
Work on the extender board is progressing, connector PCB's have been assembled into their mating plug and socket parts and the metalwork is currently being cut ready for assembly. The monitor board design is basically complete and has been bread boarded to check out the op-amp and comparator circuits. A small DC-DC supply circuit remains to be tested but has not yet been completed, once done, the monitor PCB design will be finished and sent for manufacture while the extender is wired up.
Meanwhile we have started translating the user manual "Electronischer Tischrechner Soemtron 220 - Bedienung und Ubung" that we found back in February. About half of the book is currenly completed and converted to a Word document, you can view the current state of it here, if you would like to help out with this part of the Soemtron project the original OCR text file scans of the booklet can be found here. Please bear with us as German is not our first language and we are using an online translation engine for the basic work, there are mistakes !
Then there is the Russian manual to do.......... (see below)
July 2008 -
Gerhard Just sent us a contact form this month, he has a Russian manual for the Soemtron 220 but no machine!. He has very helpfully scanned the manual and sent it over for us to look at, it appears to have the same logic diagrams but also some other different information that we have not yet seen. Translating this will probably become yet another project for us to embark on, but not for now, we will just make the pdf's of the scans available in a few weeks time. Many thanks to Gerhard for his help!.
Rüdiger Kurth has emailed in with kind comments about this site and a bit of information about the Soemtron 224. The printer for a 224 apparently was a TSD16 and photos of the printer can be found at Rüdiger's website here, near the bottom of the page.
Circuit diagrams are now complete - at last !, and just about on schedule (from our original prediction of the middle of 2008), any minor modifications to the circuits from the logic diagram generation process will be uploaded as required. Logic diagrams have been started with the diagrams for Boards 11 and 12, each with their respective sections of the Display and Keyboard. They can be found online on the Downloads page. Currently work is progressing on getting an extender card built so that we can start examining the signals on and around the boards and determin actual logic levels. A supply of suitable pins (H2170-01) and sockets (H3194-05) has been received from Harwin and our grateful thanks go to them for their help with this project. We have used their products in the past and can highly recommend them. A pcb for the extender board is currently in manufacture and should be with us soon. The extender board is envisaged to have a small ancillary adjustable LED monitor pcb so that we can examine the state of slow moving and stationary signals, although the design of this circuitry is not yet done. The extender board design will also be available from this website when we have completed it.
June 2008 -
Circuits for the original Soemtron 220 are almost complete - honest !. We have pretty much finished the drawing and checking of the circuits and with only a couple of snagging points for boards 8 & 9 to be completed we have pdf'd the circuits and uploaded them. Any changes for boards 8 & 9 will follow in a few days. These circuits represent 10 months of work to reverse engineer the boards of our original Soemtron 220 and at this time we believe they are as complete as they can be. Over these last few months and especially since Bernard Green sent us the original logic diagrams to check against, we have found that there are several errors in those original German logic diagrams which are mostly down to typos in the net names, the next job is to produce a set of modern logic diagrams using current symbols.
A recent Email from Thomas Richter has helped out with yet some more information about the Soemtron calculators - that being the operation of the top row of three register operand keys. We had them down as being "multiply" keys, they are actually combined action "Recall" and "Clear" keys. As Thomas says "Pressed once, the value of the appropriate memory is displayed, once again, the memory is deleted". Also Thomas mentions that "pressing Lö does not affect the content of the 3 memories". Many thanks to Thomas for his help and also correcting our German wording for us - oops!.
Click here for previous events in the timeline of this Soemtron website.
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