41C card reader writes but won't read


I was wondering if there are any hints that folks here can give me about repairing an 82104a card reader for the HP-41C series. I have one that will apparently write a card properly. The written card seems to read ok on another card reader. But any card that I try to read in this particular card reader, whether written by itself or by another known good reader, it displays error messages. Either "MALFUNCTION" or "CARD ERROR" and it doesn't get the program or sometimes it gets a couple of nonsense instructions.

Strange thing is that it writes cards apparently ok.

Is there someone here who might give me a starting point for troubleshooting this thing? It seems like it might be electronics, but I suspect that there are others here who have more experience with this thing who might have run across this symptom.

Any help is greatly appreciated. Thanks.



Well, I may have answered my own question. Upon disassembling the reader it appears that the head may have just been dirty. While I have it appart, though, I want to replace the wheel before it gums up the works. It is ok now, but might as well do a preemptive strike. So, the question becomes, o-rings or fuel line section? The o-ring solution looks easier and just as good, but where do I find just the right size o-rings for this? As I probably will be doing more in the future, I'll be looking for a small quantity, but more than just two.

Thanks for any ideas.



I've been dealing with a few 82104A in trouble, and both of mine use O-Rings. I do not know the fuel line used in models (planes) but I believe if they have a regular surface and homogeneous thickness, then you just need to push-it-in regularly, avoiding any irregularities when it is in place.

About the O-Rings, the final traction will happen only in both thin surface paths. I'm not sure if this is good or bad, but I understand that the risk of future stress over the card's surface in these contact paths is big; fuel lines are much like the original tractor surface, regularly distributed pressure.

Hope this helps you choosing which to use. If I have the skills and the material, I'd use fuel lines instead of O-Rings. But I did not find the fuel lines where I look for them.

Success. Let us know what happened.

Best regards.


I use the fuel line exclusively. There is a much more even uniform surface area. You do have to be careful with fuel line material to make sure you get some that inside diameter and outside diameter are concentric. That is, when installed there is a unform thickness of the tubing.

There is another area where this uniform surface is important. Since the tubing fits the shaft very uniform and with lots of contact, there is little chance of it walking off the shaft. Glue is not required.

But as o-rings tend to only contact the shaft with a small surface area, there is a more likelyhood that they will walk to the edge and rub against the reader housing.

Also, while the cost is not much for either fix, tubing is dirt cheap. You can get enough tubing for $3.00 that will fix every reader you and all your friends will ever need. It's less than 3 cents for material per reader.


Hi, Mike;

thanks for the tips and information.

Is it hard to measure or to find information about the measures for this fuel line (inner and outher diameters)? Is it the same airplane material previously mentioned here?

I'll try a bit more to find any hobby store that deals with airplane models, too.

Thank you very much.


This is what I use. Note that it is marked "MED." I should warn you that you need to check it yourself. I have seen some that is too small and some that is just right.

You might even take the wheel down and try the fit. A good fit should be forced on to the shaft. It should be ever so slightly larger than the shoulder. It is almost flush with the shoulder of the wheel.

Besides the issue with concentric inner and outer diameters, you should check for roundness. You can easily eyeball the fit and see if it is out of round. You can also spin the tube between your fingers and feel if it's out of round.


Hey, Mike;

thank you for taking your time to photograph it and save it in the provider. I downlaoded teh photo and I'll use reference to find the tube.

I'll do that: "measure" it in place, with the whell in hands. That's the best way, you're right.

Yhank you for the valuable tips.

Best regards.


I have tried both, both work, but FWIW, I feel the fuel line is better. More surface area, etc, etc. I have found the only problem with fuel line is finding stuff that is concentric. I had to search for a while until I found some that was reddish in color, I no longer know the manufacturer of this, but I'm sure if you haunt the hobby shops, you'll find some that is suitable. I do know the Dubro brand that is light blue in color did not work for me, it was too irregular in diameter.

The O-rings I tried came from Mark Hoskins on eBay. When you buy a kit from him for $5 or whatever it is, you'll get about 10 or 12 rings, enough for at least 4 readers. He sends color printed instructions as well. I don't know the actual standard number for the rings, but they measure 0.245" OD x 0.100" ID with a thickness of 0.070".

If you have no luck with the search and want a couple of feet of tubing, email me and I'll snail mail you some.


Your problem may not be just a dirty head and drive wheel. I now have three readers that will write but not read. On the HP65/HP67 the problem has always been a small blue tantalum filter capacitor. Although the capacitor will test as good, it develops a high equivalent series resistance (ESR) and no longer filters high frequency signals properly.

I have replaced all the likely culprits on one of my HP41 readers and it still does the same thing. There are a few more things to try, but I need to get the proper parts. Has anybody found a cure for this problem on the 82104A readers?


Ahh, interesting to see that some of you guys are preferring the fuel line over the O rings. What a novel idea. Musta been some kind of genius that thought of that material! ;)
Tell me this Mark Hoskins fellow isn't printing my article and selling it on ebay. If thats the case, you guys can send me a SASE and I'll send you a piece of the fuel line for free. I've been flying R/C for 28 years now and have PLENTY of that stuff.


where to? I'm having trouble locating the right size locally.

silly university town.

Possibly Related Threads...
Thread Author Replies Views Last Post
  Reasonable price for a 41C, Quad Mem, Time, Navigation and Card reader module? Eelco Rouw 10 3,067 12-12-2013, 01:52 AM
Last Post: Eelco Rouw
  hp-67 card reader problem. Marcel Samek 5 2,108 12-09-2013, 09:09 PM
Last Post: Paul Berger (Canada)
  HP PRIME: command to read the SERIAL ? Joseph Ec 9 3,915 11-01-2013, 12:43 AM
Last Post: Joe Horn
  HP-97 card reader pinch roller axle davorin 2 1,119 09-15-2013, 08:47 AM
Last Post: aj04062
  HP-97 Card Reader davorin 3 1,280 09-13-2013, 04:21 PM
Last Post: Stephan Matthys
  HP-67 Card Reader Repair Question aj04062 1 1,034 08-08-2013, 11:15 AM
Last Post: Randy
  Hp-67 card reader: tantalum capacitor identification Ignacio Sánchez 8 2,267 06-02-2013, 07:26 PM
Last Post: aj04062
  Does IR printing not work on your converted WP34s? Then read on... Harald 3 1,152 04-04-2013, 05:46 PM
Last Post: Harald
  HP-67 Read Error Matthew Richards 5 1,401 03-31-2013, 05:01 PM
Last Post: Matthew Richards
  Testing card reader motor for 65 Michae Altmann 2 1,102 03-17-2013, 09:24 PM
Last Post: Randy

Forum Jump: