During my renovation activities I came / come across mal functions at the various machines. Those are often technology- or manufacturer, electrical or mechanical related. Some commonality strokes me here. In this chapter I will try to explain these in detail for the benefit of other mechanical calculators collectors.

Electrical motor problems (Uncontrolled turning and Radio Interference Circuits)

The machines, with electrical motors, have often "Radio interference circuits" build in. These electrical circuits, prevent radiation of electromagnetic waves, who disturbs the old MW and short wave radio reception and prevent net mains pollution in general. An other function, which is often combined in the same housing, is the spark prevention on the motor on off and speed regulation switches. These sparks are caused by switching off the motor. A motor can be seen as large coil /self inductance. Self inductances generate large voltages, on the switch contacts, when they switched off. Often large enough to bridge small air gaps and sparks occur. To prevent that from happening, a capacitor and a resistor in series, are shunted the switch. The resistor limits the current, when the switch is closed and the capacitor is discharged.
The RFI circuits consists of capacitors, resistors and sometimes coils. The capacitors of both networks are often of the paper film type and have internal degradation after so many years. This has create an virtual resistor in parallel with the capacitor. This resistor, which is lowered by higher temperature, starts to heat up the capacitor and make the internal resistor even smaller. This often does the motor turn slowly. This avalanche heating effect may cause the capacitor to explode, if not quickly turn of the machine from the mains / net. Some times the dielectric, the material intern the capacitor is tar. I had one machine, which was internally completely black, due to this big bang effect.
The solution is to rebuild the circuit by replacing the capacitors with polypropylene types. These are more stable but are difficult to get in the voltages in axial packages. Printed circuit mounted types are more usual these days, but bigger and often not possible to pack in the same location / housing. (See Hamann 300B, Astra 110, Walter SRM-13 machine stories on this web site)

Electrical leakage to ground / earth

The RFI capacitors, I have mentioned above, have capacitors between the mains and earth potential. When these capacitors are degraded their mentioned parallel resistance is caused an current to earth. This switches off the mains safety switch. My suggestion is: Leaf them open or replace those with polyprop ones to when you tend to restore the original circuitry.
Next leakage reason might be motors with brushes. They tend to pollute the surroundings with carbon. This is electrical conductive and caused sometimes leakage currents to the metal cases and earth potential of the net. This will switch the mains off as well.
Cleaning the carbon parts with washing petrol or turpentine is the solution. Soap is possible as well but be aware that sometimes the isolation of the motor wiring is of textile and moisture is getting the problem even worse.

Degeneration of capacitors

I have personal no experience yet of degenerate those capacitors, but highly experienced friends have. When someone has those to, or have procedures like warming up the capacitors or others and know the phenomenon behind, please let me know!!

Completely blocked machines by hardened oil

Some machines I have, were completely blocked by dry out oil. Oil looses his viscosity during a long stay and turn into a more resin type of material. In that condition oil has lost its prime properties where it was put on and build up more and more a resistance to movement of the parts / friction, with the final effect of blocking the machine. Turpentine is solving this resin / oil, but it has not immediately the power to penetrate in to the critical places. Especially plain / sleeve bearing type of constructions. Long axis with daisy chains etc. are the most difficult to get loose again. (Please see the Madas and Continental machines). Time is needed and sometime W40 spray ore other more aggressive penetrating oil is needed.
A more aggressive method is, using cleaning chemicals like oven cleaners (Mr. Muscle or the like). But please be aware that these attack the paint and old electrical parts of wire isolation as well, so use it on the metal parts only. Heavy cleaning with warm water is needed afterwards. I use a compressor to dry the machines after the action. W40, which is pushing the water away as well and lubricate the machines will bring the machine in good condition again.
The picture to the right is an open Continental full key board adding machines. The movement of the keyboard plates is often not possible due to the above mentioned reason, to much force is needed for proper calculations. Resulting in obvious calculating failures at many digits.
The critical area showed in more detail on the picture below. The main axis has a plain bearing with a flange to keep the segments in position. That's why this relatively large flange result in the great friction surface. Earlier types can be disassembled, like the one below, but later ones are fixed by not easy removable steel pins.
Besides the petrol or so on the axis, is it possible to perform a little manual force to get the blades turning again.
This by pulling and pushing on the key board plates. This is of course only possible when the plates are free movable. This is the case when the crank pulling is just before the maximum deflection of the key board plates is reached. It will stayed in that position and will not turned back.
Penetration oil will help of course, but I have the feeling that heavily cleaning is needed afterwards, to prevent long time unwanted effects.

When numbers printed only half (bottom)at rocking segment machines, you might look to the attenuation if that is still operational. I g

The register resetting of Pin Wheel machines have often the same type of failures. The reset lever has to shift on an shaft. Due to hardened oil this lever mechanism is fixed on the shaft and this prevent them from functioning. Manual shifting in both directions to get them loose again is the solution.
At the handle often a lever sets the movement of the pin block free. This is often locked as well.

Pin wheel start turning is not possible. This is often the mechanism that comes free when the handle is pulled out of the rest position. This should, via a lever mechanism, get small shaft in the main Pin Wheel free. Due to ?? this sometimes sticks to the shaft. Manual force will mostly get that
Renovation Experiences