41cx Card reader problem


I just repaired my card reader for the sticky wheel problem and after a few tries, got it back together. Thanks to everyone who has posted ideas on this site about this repair (I used model airplane tubing). Now the problem. I can write a program to a card, clear the memory and then read it back in, so I know the reader is working. What I can't do is read all my old cards. When I run them through, I get a checksum error, or a card error message. Sometimes I get the 1 of x message, but it still won't read. I have run the red cleaning card through, but it does'nt seem to help. And the cards are clean.

Any ideas would be appreciated.


If you can try those cards in another reader or calculator to be sure they are alright.


Did you ever, by any chance, have a calculator with a clock speedup?

I know that with a speed increace of more than something like 40% (not sure exactly) that the cards you wrote would not be readable on a normal speed HP41 (not sure if they were readable on the souped up one though).


I originally had a CV until it was stolen, then I got a CX. It too dissapeared years later. I can't remember which one I wrote these cards on, but none of the cards have been used in the last 10-15 years. I just got a used CX. I know the first two were never modified by me, but I don't know about the latest CX. Is there a way to tell?



The "beep" is a dead givaway. It is considerably higher pitched when sped up.

I have had a "spouped up" HP-41C for more than twenty years. Mag cards are interchangeable with my other 41CV and CX with no problems, both reading and writing. It's a little over 40% better than the normal speed. It also has no trouble with either the HP-IL or the wand.

The stripes are considerably denser on mag cards written by this machine. Someone demonstrated this once with fine iron filings in (i think) an alcohol solution. Nevertheless, the cards are fine, and still readable by other machines after almost a few decades.

The mods to my machine were done by a friend at the time, and he'd followed instructions in one of the PPC Journal issues.



did you try to read your old cards in another reader? Maybe your cards are too old. You said you have not used them since 10 or 15 years, thats a long time. :-)



You may have a problem with head alignment, if it can write and read cards since it has been fixed but not read older cards. I would think even a small alignment problem would make it difficult to read the old cards. Randy


The type & OD of the tubing you use can have an effect. Too smooth (clear vinyl type tubing) can slip a bit during reading. I prefer a rougher surgical tubing which grips the cards better, though you may be able to roughen the smooth tubing with fine sandpaper. Also if the OD is not correct the speed of the card may be different from when recorded. This can often explain why you can read and write a fresh card, but cards written previously on different machines may not read correctly.

Good Luck!


Some comments:

Cards getting old: time will not damage your cards, but dirt, grease, magnetic fields and heat may damage them.

Speed considerations: I think the cards are written with a self clocking signal, or with a clock track (written at the same time than the data). This allows for some speed deviations without causing problems. Of course, a large deviation may be out of range and cause failures.

New pinch roller: In my own experience (may not be your case), the airplane model tubing was not circular enough, and that caused slipping and speed irregularities. I had better results after a second repair with rubber o-rings.

Head alignement: good suspect because you can read newly written cards, but nor cards previously recorded. But not easy to detect and correct due to the mechanical construction of the reader. You may check if the head is properly seated, etc...

Dirty head: bad suspect, it should affect both new and old cards.

I hope some of this may help as guiding ideas.


Thanks for all the info.

The new roller may be suspect as I did have to go through some tubing until I found a section that looked concentric. I think I'll try the 006 o-rings.

I don't think the head alignment could be it since the head is firmly glued in place and has not moved. I dont think there is any room in the slot for the card to get too far off track. The springs are in the correct place.

I'm trying to find someone locally who might have a reader, so I can try these cards on another machine.

One weird thing. If I put the card in track one first, I get a card err message, as soon as the card starts through. If I put it in track two first, I get a checksum error, and then when I pull the card out, it will say rdy 01 of n where n is a number larger than the number of cards in the original set. Could there be something set in memory, where it is looking to complete a data set, and won't accept anything now that I have it so confused by trying a bunch of different cards from different card sets. I have done the backspace on trick to get a memory lost message. Is this all there is to clear everything, or is there some other trick.



Your cards would have worked fine if you had sent me a postcard in exchange for the article.
And to you guys at the camera shop "down under" I'm still waiting for my Duck bill platypus postcard! :) Dave

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