HP-67 Card Reader became very touchy

[Hiwi]

(11-05-2023 07:09 PM)Alevin Wrote:  Was the Hp-97 serviced, and being C3 dead, another one was inserted in the motor? repair simpler than desolder and recap?

No, this is a common design rule to eliminate a so called 'brush fire' of brushed motors. (FCC)

This cap should be placed as close as possible to the brushes.

The motor cables work like a an antenna for the HF/LF signal, which can disturb electronics inside and outside the calculator. The cap shorts these electrical interferences.

I have never seen any cardreader without this cap (HP41/HP67/HP97) Same as with printer motors in the HP97 or the HP82143/162

Ralf