R-HP 97 internals and repair

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This calculator was in a nice condition but it had no battery inside. Ones a battery was assembled from Sub-C NiMH cells, the printer nor the card reader worked.

A lot of information can be found on the internet, in particular on http://www.hpmuseum.org and http://www.rskey.org/

The card reader contains a rubber “wheel” which drives the card. In my machine the rubber was totally gone. It more looked like over-aged chewing gum. I replaced it by silicon tube used in model air planes. The “rubber” also blocked the little plastic balls which drive some switches that take care of timing of the reader.

The printer didn’t transport the paper anymore. The two small plastic transport wheels contained a dent probably caused by long storage. Careful removing most of the dents with some fine waterproof sandpaper was enough to get them going again.

Both the card reader and the printer still work fine two years after this repair.

The original battery pack contains Sub-C cells with a rather low capacity. From a charging point of view NiMH is not ideal. The charger is not designed for this type of battery. However NiMH has two advantages:

A large capacity because of which the low capacity charger will not damage the cells.
NiMH is available in types with very low discharging current when stored. So we don’t have to check them often for low charge.