Diehl DSR18

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Repair Info

This calculator didn’t function on arrival.  However, it was reasonably clean and obviously taken care off.  Only the motor area was dirty and covered with carbon dust mixed with aged oil.  That  was to be expected.  All spark and RFI reduction appeared to be removed.  One consequence was the heavy sparking motor.  The resistor which generally is part of the speed regulator was missing as well.

So one of the first things after a first clean was restoration of these electric parts. For the spark reduction I used values that I saw before:
0.1 uF capacitor + 100 Ohm resistor.  Two of them are necessary, one for the motor and one for the switch that operates the motor.
For the speed regulator I took a guess by using  a resistor of 1300 Ohm  (actually two 2600 Ohm 10 Watt resistors in parallel).

For the rest this machine only needed cleaning and oil to get parts smoothly moving again.  It toke quite some time and wasn’t  always easy.  They are complex machines and in detail always different in the way calculations are controlled.  A user manual is not always available. In this particular case usage information from a fellow collector made it a lot easier to understand how the different parts of the control mechanism are supposed to work.  After all, a general clean will seldom result in a working machine.   Finding and cleaning individual blocked parts is nearly always necessary.

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Spark reduction circuit

RFI reduction circuit