HP 41 magnet card reader- mechanical problems-


A few days ago a colleage gave me his 20 years old card reader for my HP 41. As I started trying it, there was an dull sound, like the e-motor got stuck, the inserted card was not pulled through the reader anymore.

After I get some informations about repairing the card reader, I disassembled it, removed the rubber from the rubber-gear-wheel compenent (because the rubber got a jelly like feeling, an the tiny white roll was sticked on the rubber roll), I cleaned the whole mechanisim in put two small o-rings on the shaft, assembled everything and was very happy, that it worked fine, but only for a few moments. After a short time there was the same dull noise, like the motor or the gear was blocked.

So here are me questions:
1. Are there any recommendations for the o-ring size?
2. are there any alternatives for using o-rings?
3. Is it necessary to grease the whole mechanisim, and if yes, with what kind of lubricant?
4. Do you guys had similar problems with the card reader and how did you solve them?

I know this are many questions, but it would help me a lot if I can get my card reader back to work (there are some nice progams on the cards ;-) ).

Thanks a lot in advance.



my answers would be:

1)yes, there are o-rings that fit in. If you have a measuring instrument, simply take the inner and outer diameters of the metal gearwheel where the o-rings are built. The closest measure of the o-ring, the best (try o-rings slightly tighter in the inner hole). If you feel confident, you can use a very, very, very small amount of silicon-based glue to fix the o-rings in the gear. This leads to the fourth answer I'm placing right now:

4) Yes, I had a problem like this: stuck cards. I disassembled the reader and saw that the o-rings simply moved out of the gear and touched the plastic structure. At this point I decided to use silicon-based glue: a very thin layer only where the o-ring would touch the gear, and another thin layer between them both. No more problems.

2) the other alternative shown here is fuel tubes used in modeling (planes). There are several inner and outer diameters. Many guys in here prefer these tubes; I simply did not find any of these closer to where I am.

3) I would not use lubricants. I do not remember seeing any, mostly because it's a slow-movements mechanism, moving gears are plastic over metal, and the magnetic card itself has a lot of contact points when being read or write.

I have one working reader with silicon-glued o-rings, no lubricants at all (they may leak and touch cards' surface, right?), working perfectly fine after more than fifteen years with me.



If you do use O-rings (not recommended here) you need size 005... 15/64 OD. You probably cant find them... and normal size 006 (1/4 OD) are too big can cause the mechanism to bind. I always use silicone rubber fuel line. The problem is finding it that is actually truly round with a centered hole.

Anothe problem that can develop is the worm gear coupling to the motor drive shaft comes loose. It was origianlly friction fit. Cure here is to make a new coupling (you need a precision mini-lathe), glue the coupling with a drop of rubberized super glue (my recommendation), or shim the motor shaft with thin plastic (like a grocery store bag). I have found that shimming often causes the couling to break into several pieces that can't be repaired.


You can try this repair kit, it includes the instructions and a pack of O rings.



Have you removed the motor from its plastic mounting plate?

You should do this and check if the cog and drive wheel is free to spin. If it does not turn very easily then you need to dismantle it completely and clean oput any gum which is deposited in the pivot.


Hi Martin,
I know it sounds very silly, but is it possible that you did not use fresh batteries when you tried to get the reader to work? Sorry, but I am asking this question because you are saying you got the reader a few days ago. I understand it as you never had any before. If I am wrong, please forgive me, if I am not, use fresh batteries (the motor draws really high currents). I often have a motor stuck when I use the reader whithout recharging my NiCds before using the reader.
Regards, Andreas

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