Feature  

Description 

Case:  

Metal

Color case:  

Grey / Beige

Color keyboard:  

Grey

Weight:  

15kg

Voltage selection:  

110-127-220-240V

Adapter:  

N/A

Power consumption:  

Working condition:  

Printed Circuit Boards (PCB's):  

PCB 01: 05-220-7012-3 (3044) (near the power supply)
PCB 02: 05-220-7011-5 (3043)
PCB 03: 05-220-7010-7 (3042)
PCB 04: 05-220-7009-2 (3041)
PCB 05: 05-220-7008-4 (3040)
PCB 06: 05-220-7007-6 (3039)
PCB 07: 05-220-7006-8 (3038)
PCB 08: 05-220-7005-1 (3037)
PCB 09: 05-220-7004-3 (3036)
PCB 10: 05-220-7003-5 (3035)
PCB 11: 05-224-7002-5 (4638)
PCB 12: 05-220-7001-0 (3033)

Memories:  

3

Memories indication:  

Prog. steps:  

N/A

Decimal point handling:  

Via switch on keyboard '0-1...'-position.

Rounding:  

Calculation overflow indication:  

Input overflow indication:  

Divide by Zero indication:  

Square root of negative value indication:  

N/A

Negative value indication:  

Constant function:  

Auto Power-off:  

No 

Display details:  

WF: Z570M (648)

Printer:  

N/A

Extra features/remarks:  

(Many thanks to Bernard GREEN from the UK for the technical info):
This calculator has 15 digits add, subtract, multiply and divide and square.
There are 10 different places for the decimal point set by the wheel on the left side of the keyboard, the decimal point is indicated by a small white lamp between
the Nixie display tubes. There are three separate memories, each 15 digit with add and subtract read and clear. These are the 12 keys on the right of the keyboard.
[C] is clear entry and [Lö] clears everything including the 3 memories.
The keyboard is made with V23 Microswitches and a separate wire
to the logic for each key.
There is a ferrite core store memory with six 16 digit registers (PCB 12).
The logic is all flip flops, each made from 2 PNP germanium transistors, about 10 resistors and two capacitors. There are AND gates and OR gates made from diodes and resistors. Flip flops have toggle inputs and set or reset inputs with a capacitor
and diode and a resistor. The voltage on the resistor either enables the input or disables it from affecting the flip flop. One flip flop has about 25 inputs.
The logic design is very interesting. The machine was made in Sommerda in the
old East Germany about 30 Km west of Erfurt and the poor quality of components (many from FEBANA in East Germany) made the early machines prone to error.
The transistors seldom failed but the diodes were frequently failing.
Later models mid 1968 (?) were fitted with a better quality diode, but then the SHARP Calculators were taking over the western market and the SOEMTRON sales were confined to the eastern block.
The calculator doesn't like working in a draft ( moving air ) or near a fan because there is a thermistor placed near the ferrite core store to sense the temperature and control the voltage for the core store drivers. If too much is moving through the machine, the thermistor doesn't measure the temperature properly and the
wrong voltage meant the cores didn't read write properly.
Service people made a point of checking voltages regularity and found they drifted over time from the correct settings.
Another problem with repairing the 220 is the need to have at least one board on
an extender to enable getting test probes on the circuits. Some modules are split between two or more boards and these require two or more boards on extender cards. There was a test box (Prufgerate) available which had a lamp for each flip
flip and other important circuit nodes. This plugged into the two multi-pin sockets above the sockets for the keyboard, display and power unit. This was almost an essential for servicing the machine.
The best test is to divide 7 by 9 with the decimal point set at
14 which gave an answer of 0.77777777777777 after about one and a
half seconds with the display rippling through as it calculated.
In 1977 the production of the 220 did stop.

Initial price:  

In 1968 the machine did cost about £400 in the UK.

Overall quality rate (1-10):  

8

OEM-copies:  

Other sources of info:  

First of all: the great documentation from: http://www.soemtron.org/
FROLOV Serge, ROBOTRONTECHNIK, UNI-GREIFSWALD

Advertisements/Publications:  

Manfred SPERFELD:
Elektronischer Tischrechner Soemtron 220 - Bedienung und Übung,
Verlag Die Wirtschaft, 1972, 63 pages.