HP-97 card reader repair

[Brian Keller]

I have a HP-97 that is in good shape and works well except for the card reader. I went through all of the repair steps provided by Steve L. at the HP Museum, including testing the feed of a card using a classic battery pack. That all went well. But when I reassembled the unit everything worked except for the card reader. It appears to not detect the card insertion or does not have power to the reader.

Anyone know what might be wrong? I know the motor and my new pinch wheel work. Could it be the ribbon cable or is there a microswitch in the reader which detects card insertion?

[Andrés C. Rodríguez (Argentina)]

Such "microswitch", at least on the handhelds, is made with a long and thin, elastic, gold-plated "leaf" that arches when pushed on one end, so making contact with the printed circuit board. Now, what makes the leaf bend ? A small plastic piece (sort of a cylinder, no more than 2 mm in diameter), that protrudes on the card track, and that is pushed by the card. The cylinder, in turn, pushes the "leaf" and, forcing it to arch and close the contacts, signalling the card insertion. Please disregard any idiomatic mistake, I hope this may help you.

[Brian Keller]

Thanks for the help!

[DaveC]

As Andres says there are microswitches (leaf contacts) but if you didnt touch them they are probably OK. Chances are that your ribbon cable has not been inserted correctly or the conductor has flaked from the backing.

[Brian Keller]

Thanks for the advice. I will look more carefully at the ribbon cable because I was very careful with the gold leaf so it should not be that. Thanks again!