HP 82104A "CARD ERR" error

[wongkarcanada]

Greeting. I am a newbie to HP calculators and to this forum. Any help is appreciated.

I collect calculators though mostly Casios. I recently acquired an HP 41CX, which comes with a card reader with a bunch of new and used cards. The card reader didn't work at all, of course, since the original roller had long ago turned to goo. So I purchased a "repair kit" consisting of proper sized O-rings. I have repaired the reader so that it is now mechanically pushing the card through. However, any time the cards (previously recorded ones) are pushed through the display shows "CARD ERR". Not knowing if the cards actually were valid I found the "WALL" command as well as the "VER" command. None of the new cards that were written by the "WALL" command could be verified with the "VER" command (or could be read, for that matter). So it looks like the card reader is not able to read cards at all.

So what would be the common reasons that would cause the reader not to read cards? The inside of the card reader appeared to be in good shape with no obvious signs of damage. The R/W head looks OK as well.

Thanks.