Prüfgeräte
Test Equipment

Production testing

Above ©1995 DESOTRON www.desotron.de

Eight channel monitor

Extender

Two pictures above ©2011- www.soemtron.org

Prüfgeräte (test equipment) used by V.E.B. Büromaschinenwerk Sömmerda for the Soemtron range of calculators no longer exists having been scrapped when the factories were closed many years ago. A photo (right) of the Soemtron 220 production line, shows several of the test stations with Prüfgeräte and oscilloscopes, both of which can be seen in the photo to the left of the white coated technician with his back to the camera. Click any image for a larger version.

In the Russian technical manual for the Soemtron ETR 220, Chapter 5 “Maintenance”, from a short section reproduced (here), details the use of the Prüfgerät in the case of faults that cannot be diagnosed with the logic diagrams, describing that - “the display panel of an electronic invoice machine « Soemtron-381 » of the type 8601 is connected”.

All of the machines in the Soemtron ETR 22x range had a set of internal "service" connectors which were used to connect a Prüfgerät to the various internal signals of a machine under test which would then allow further diagnosis of any faults. With the description in the Russian manual that the Prüfgerät was for an “Electronic invoice machine Soemtron-381 type 8601”, it would seem that these "service" connectors were a common design feature in both the ETR 22x machines and other complex digital electronics product produced by V.E.B. Büromaschinenwerk Sömmerda at the time.

With no information about the internal structure of a Prüfgerät, other than the front panel outline drawing in the Russian manual and the photo above, we have designed our own. Using connections derived from the 220 logic and circuit diagrams, Bernard Green's recollections that the Prüfgerät contained “high impedance” inputs, our own 220 222 and 224 machines along with whatever other data we could collect, this circuit has been put together. Quite a lot of the circuit has been based on the eight channel monitor board we designed a year or two back, but we have gone a little further than the original Soemtron Prüfgerät and added a couple of four digit panel meters to monitor the internal supply voltages, very useful when setting the memory core supply voltages against temperature.

1. Overlay drawing of the Prüfgerät front panel with connections.
2. Pages 184-186 from the Russian Technical Manual detailing the Prüfgerät and it's usage.
3. Service connector signal differences for the Soemtron 220, 222 and 224 machines.
4. Prüfgerät circuit diagram.

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