The HP-82104A card reader repair by Peter M. Geiser


Old HP card readers often have the problem that their gummy wheels start to become "gooey" after a couple of years. This causes the cards to no longer being accepted, and even worse, to be damaged. This guide is intended to give some help to someone wanting to repair a card reader for a HP-41C, HP-41CV, HP-41CX, HP-41CY, etc.

The solution is to replace the gooey gummy wheel with a new one. This can be silicone tubing (as for airplane fuel) from your local car or airplane model shop, or alternatively O-rings. Repairing the HP 82104A is easier than repairing the HP-67/97. This is mainly due to the easier accessibility of the gummy wheel. Still, it is advisable to work carefully.
One note of general caution for the screws: some screws are difficult to loosen, and too much force or the wrong screwdriver may destroy them. Apart from using the right size equipment, make sure the screwdriver is put firmly on top of the screw, and turn gently, slowly increasing pressure until the screw comes loose.

Disclaimer: I am not affiliated with Hewlett-Packard. This guide is intended as an idea of how a card reader could be repaired, without claiming to be complete, or accurate. Use it at your own risk and judgement!

Click on the thumbnails to see the full image.

Picture 1   

Carefully remove the label on the back of the card reader. There are several ways to do that. I used a benzine (Wundbenzin in German) to make the glue less sticky (I assume that isopropyl alcohol would also do the trick), and took my tiny Swiss army knife (others had success with a razor blade.)

Picture 2   

Under the label there are three screws.

Screw (1) is for opening the case.

The two screws (2) hold the reader itself (the part with the motor) in place.

Picture 3   

Remove the lower of the two screws (3) on the front plate.

Picture 4   

Here you see the opened reader. Make sure that you carefully lift the unit with the motor off, and make sure you do not damage the fragile pins that make the electrical contact.

Picture 5   

This part comes off after removing the screws (2) at the back of the reader.

You should leave all the wiring in place, but just in case one comes loose write down the locations of all cables.

Picture 6   

Here you see the gummy wheel, held in place by the black pin indicated in the picture.

Picture 7   

The wheel is not yet very gooey, but brittle, and goo has started to stick to the magnetic cards.

Picture 8   

To get to the wheel, you need to remove the motor. Remove the indicated two screws (4).

Picture 9   

Carefully remove the plastic pin. This involves some force, but this force needs to be applied with a lot of "feeling" (i.e. very carefully.)

Picture 10   

These are the various screws you have removed so far.

(No, you should not have removed number (5), this was an error on my part and is entirely unnecessary.)

Picture 11   

Underneath the gummy wheel is a very small plastic roller. Make sure you do not lose it.

Picture 12   

These are the parts you just removed:

  • The pin
  • The wheel, with the newly attached o-rings already in place.
  • The white plastic roller.
Picture 13   

Reassemble the unit:

  • Put the white plastic roller back in place.
  • Put the refurbished wheel back in place, and fix it with the plastic pin.
  • Reattach the motor with its original screws (4).
  • Put the motor unit onto the back-plate. Make sure the five golden pins are in the holes and have contact. Note: The motor unit has quite an angle to the back plate.
  • Re-screw the screws (2).
Picture 14   

You can safely test whether the card reader works without reassembling further.

Picture 15   

The pins with the holes for the screws (3) need to fit into the top of the card reader case. Put them in nearly to the top, with a very small space as limit.

Picture 16   

The final assembly of the case is actually quite tricky, and I needed all "four" of my hands ;-), so I couldn't take pictures.

Put in the latches, and make sure the attached springs fit behind the pins from the previous picture. There are small holes on both sides, so that these latches can move relatively freely.

Make sure that the curved front piece fits. The latches still should be moving, but not freely anymore.

Then, fasten the screws (3) back on.

Put back screw (1).

Finally, re-attach the label.

I wish you success with repairing this beautiful piece of vintage technology. Let's hear about your experiences!

(Republished with permission of Peter M. Geiser)


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