HP 41 card reader repair questions

[GreyUser]

The malfunction message is an usually an indication that one of those switches is not making contact.

The most common cause is mis-alignment of the two small whiskers that protrude from each leaf with respect to the circuit board. If the board slides up or down before being located on the alignment pins, the whiskers don’t align correctly with board contact points and the switches do not function, ohmically. You can usually coax the whiskers into the proper position with a small strip of heavy paper by sweeping the paper strip in the direction of card travel. You must check the switch function with an ohmmeter if you don’t want to go nuts assembling and disassembling to get things working.

Aide from the obvious mechanical mis-alignment issues, oxidation on the leaf switch contact points or the board contact side can cause the same problem. This one is typically caused by outgassing of the failed urethane drive wheel. My usual approach during wheel replacement would be to clean the gold board contact points with a clean pink eraser and use de-oxit D100 on the leaf spring contact points.

Additionally, it can due to the whiskers or the leaf itself having been bent out of true during a previous repair attempt but this isn’t common, the parts are pretty robust, given their size.

You did set the motor current with the eccentric cam, correct? Can you point me to repair procedure that you used?