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Thoughts on HP 82104A card reader repair - Printable Version

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Thoughts on HP 82104A card reader repair - jjb299 - 07-02-2014 02:44 PM

I wanted to share some of my experiences repairing a HP 82104A card reader for the HP 41. I recently acquired this card reader and it definitely had a gummy wheel. I enjoy repairing HP calculators so I was anxious to get started on this project.

The two best "how-to" guides I found are listed below. I read both of them top to bottom because both of them cover some things the other does not. Very useful.

Link 1
Link 2

Regarding the white roller (Link 2, Pic 11): I found mine to be too snug in the bushings that hold it. The roller would not roll in place if I tried to move it with a pencil. I was able to expand out the plastic bushing area with some tools to allow the roller to spin freely in place. I think this improved card advancement operations. The tiniest amount of white lithium grease (applied with a needle) provides those with OCD some additional comfort.

Regarding the new rubber roller (Link 2, Pic 12): I opted to use the "o-ring" solution rather than the "fuel line" solution that is mentioned elsewhere in the site. However, the dual o-ring shown in this picture may not be the best option. As it is shown, the white roller will be situated directly between the peaks of the o-rings. Ideally, the peak of the white roller and the peak of the o-ring should be aligned. Also, the inner most o-ring is lined up at the very edge of the magnetic card (half grabbing the card, half grabbing the opposite side of the card tunnel). Therefore, I opted to go with a single o-ring that is directly lined up with the white roller and secured to the gear drive with super glue. I used a 1/4"OD,1/8"ID o-ring. However, another link I saw mentioned this is slightly too big OD. They mentioned the 15/64"OD is better. I agree, but I couldn't find those locally. So I carefully turned down the 1/4" o-ring until my calipers read around 0.24". This had the bonus effect of flattening the contact surface of the o-ring to increase the surface area, and it also exposed the softer (more grabby) rubber inside of the ring instead of the polished outer surface.

Regarding the "clutch" or "coupler": I found this link to be useful:
Link 3 (http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv019.cgi?read=163396).
My card reader's clutch was definitely deteriorated. (Basically, I'd recommend to anyone who has a gummy wheel to check the "clutch" coupler at the motor shaft. It's probably a 99% chance it's bad also.) So I cleaned out the aluminum cylinder, and also cleaned the motor shaft and brass worm gear. Then I used the "wire insulation" method used in the link above. However, I only used the insulation as a filler for the cylinder and to provide good material to bond with super glue. I agree with some posters that this connection isn't supposed to flex or slip; the motor can be stalled easily. So I went with a permanent solution.

After all that work I'm glad to say the card reader works like a champ. I've run the same card through the machine about 100 times and it didn't mis-feed or jam at all. I've yet to check the write protection feature or a HP67 card (the latter I don't have access to). Until then, I'm enjoying the whopping 200 bytes of data per card. Hope this post helps someone else out there.

RE: Thoughts on HP 82104A card reader repair - Geoff Quickfall - 07-02-2014 04:56 PM

Glad it works!

By the way, it is not a clutch. It is a dampener, designed to take the vibration caused by the motor out of the reader system. This is why the reader appears noisier when crazy glue is used to fix the gooey rubber in the dampenere sleeve.


RE: Thoughts on HP 82104A card reader repair - John R - 07-02-2014 06:48 PM

(07-02-2014 02:44 PM)jjb299 Wrote:  Hope this post helps someone else out there.

It certainly will! I've got two of these awaiting repairs, and while I had read the first two links you posted, your additional comments and lessons learned will help significantly. Thanks for taking the time and effort to share your experience.