Card Reader motor - doesn't spin smoothly


Hi all, I have two motors from HP41 card readers that don't spin smoothly, they're kinda "jerky" if that makes sense. Yet other card reader motors I have spin smoothly.

Does anyone know the cause of the jerkiness ?, and a cure ?? Or perhaps it's nto really a problem ? I am yet to test that.



Have they been rebuilt since they were new? All calculator card readers have rubber rollers that break down over time. Please check the "articles" section of the forum for more information and links to articles about repairs.


Are you talking about the actual motor by itself, or the action of the card reader when pulling a card through? If the card reader action is jerky and/or noisy, it could be a slipping coupling (AKA clutch) between the motor shaft and worm gear. These couplings deteriorate and break down over time and need to be repaired.


Thanks for the responses. I am referring to the motor itself, well the worm gear anyway, so I guess that means motor and clutch. I have already done the roller repair on this one, but it still throws up "Malfunction". I am pretty confident the roller repair is ok, as the other four card readers I did the same repair to all work fine :-)

Any clues ? Perhaps it's the clutch ??



Yes, the coupling (clutch) is the probable culprit. I have repaired the coupling using some wire insulation. Geoff Quickfall may have this written up by now (it's his idea), but if not I can can pm you with more details.



I had some issues with the first card reader I repaired because after having the 'gummy wheel' replaced by two o-rings, the motor was somehow noisy and [MALFUNCTION] was shown in almost all card reading sessions. I inspected the gear which gummy wheel I replaced and I noticed that the external portion of the axle (thicker than the rest of it) had a cut (for a screw driver?) and a small guiding mark. I removed the card reader from the calculator and inserted a card in the card slot till it touched the o-rings. Then I adjusted the axle by gently turning it (either clockwise or counterclockwise) with a screw driver till I felt the lower pressure possible over the card while gently trying to insert it. Then I tested it again, and the card passed faster with almost no extra noise, I could only hear the actual motor noise. Since then, I adjust the axles accordingly.

Hope this helps.

Luiz (Brazil)


Kind of busy right now but not enough to abandon the forum!

The dampening couple (motor shaft to worm gear):

Now we know why it is called a 'dampening couple' by HP! The couple to the worm gear is composed of an aluminum tube with the same type of rubber that the pinch roller has. Thus it suffers the same degradation over time that the roller does (bacterial infection has been suggested.

Hello Luiz, was the card reader you refer to from a 65, 67 or topcat (see below with reference to the HP41C series)?

The pinch roller axle (eccentric cam}:

In the HP 67, topcats and 65 the pinch roller axle shaft is assymetric allowing the pinch roller to raise or lower relative to the card reader horizontal axis. Luiz is correct that this may be a source of the noise or slipping of the card in the reader. The height of the pinch roller affects the card reading speed; slipping of the card inside the reader; again in my examples. It also raises, or put another way, changes the way the card presses against the card reader head. This to affects the ability of the card reader to read the card.

In the HP 41; at least the 15 I have restored to date, the axle is not assymetric (edtited: this is not correct as the axle is eccentric, Feb 25, 2010).

The motor itself may have very worn or corroded brushes causing the jerkiness. Have you powered the motors by a 1.5 volt battery outside of the housing, or at least while not attached to the card reader worm gear. Is it jerky.

Here is a sample of a fix Michael was refering to for the worm gear couple taken from my presentation at HCC2009 and will be found in my book. It refers to an HP 41C assembly. Notice the shaft of the pinch roller axle is not assymetric. Also, the HP41C series of card readers and the 65 (I have not compared them to a 67 or topcats) does not have interchangeable motor shaft/worm gears. They are of a different length and will not fit when the motor is placed back in the card reader assembly:

HP-65 	drive roller axle: 	8.32mm
HP-41C drive roller axle: 8.23mm
HP-65 worm gear length: 14.43mm
HP-41C worm gear length: 14.36mm

Original assembly removed with NOISY dampening couple:

Couple components:

a. motor shaft
b. aluminum tube
c. part of the urethane rubber couple material
d. worm gear

Using wire insulation, two diameters, one inserted inside the other to accommodate the larger worm gear attachment diameter and the narrow motor shaft attachment.

Completed and assembled:

Interesting photos of the pinch roller from an HP41C assembly showing the bacterial infection in full force (H1N1 for the HP 41C):

Edited: 25 Feb 2010, 11:49 a.m. after one or more responses were posted


Hi, Geoff;

the first card reader I repaired was an E-version 82104A, the one that shows [CARD READER] header in CAT 2 instead of [CARD RDR vn], where vn is the version identifier. Now that you mention about the axle shaft (missing term in my previous post... Sorry!) of the 82106A not being asymmetrical, I feel confused... In fact, after repairing the first one I had the issues I mentioned, rotating the shaft allowed to correct it. Since then I repaired about four or five card readers and I used the same o-ring in all of them. Because of this, I rotated their axle shafts to match the same adjustment I found in the first one and they worked fine. Based on what you wrote, I see no explanation for the correct operation of the first card reader since the axle shafts are symmetrical, and in the other ones I could have left the axle shaft in any position that it would not affect final operation.

Why did the guys left the alignment dot and the screw driver slot in the axle shaft if they have no purpose? Go figure...

Thanks for the very impressive photos and for your comprehensive descriptions. Very clarifying and totally useful. The solution of using wire insulator to fix the worm gear and the photos showing it are priceless! Thank you and Michael for that!

Best regards.

Luiz (Brazil)

Edited: 24 Feb 2010, 8:03 a.m.


ciao a tutti,

very nice pictures Geoff, I don't want to be blasphemous, but should I feel guilty because I simply put some glue to fix the clutch problem ? Cheers everybody, Alberto



In the HP 67, topcats and 65 the pinch roller axle shaft is assymetric allowing the pinch roller to raise or lower relative to

the card reader horizontal axis. Luiz is correct that this may be a source of the noise or slipping of the card in the reader.

The height of the pinch roller affects the card reading speed; slipping of the card inside the reader; again in my examples.

It also raises, or put another way, changes the way the card presses against the card reader head.

This to affects the ability of the card reader to read the card.


In the HP 41; at least the 15 I have restored to date, the axle is not assymetric.

Rotating it in its socket does nothing to position the pinch roller.


maybe you have special HP-41 card readers, but _every_ HP 82104A card reader I repaired so far (and it were many) does have an asymmetric pinch roller axle,

and adjusting this axle with a screw driver does have a very direct impact on the pressure between the gummy wheel and the small white counter-wheel.

The influence may not be obvious if you use O-rings as wheel replacements, but O-rings are no good solution at all,

since even in the least-pressure position of the axle, they apply too much unbalanced pressure towards the counter-wheel,

and thus the mechanical force to the complete transport mechanism is higher than needed.

This in turn can lead to effects as stated by the OP,
to more battery drain than needed, and to more wear than needed.

A much better solution than O-rings are silicon tubes, but suitable ones are hard to get.





Luiz and Raymond, good to get corrections and thanks.


Just printed out a response and lost the whole thing trying to save it.

The topcat manual refers to eccentric cams. I do not have an HP 41C repair manual so I cannot find the reference. My observation of the 41C reader is that my versions were not eccentric. It maybe that the eccentricity is much less visually then the classics. Also I have been fortunate with the 41C repairs as they have not needed to be rotated to allow the reader to work, maybe just luck.

The 65, 67 and topcats have needed rotating as per the manual.

I think I will have to tear down another, (sitting on the desk) and look again.

Thanks for the info, could it be that some later versions were not eccentric?

Cheers, Geoff

P.S. take a close look at the black cam in the photo. You can see the right hand tip that fits into the back end of the asssmebly is in the centre of the shaft, or visually, extremely close to centre. The slotted end also has the shaft protruding from the centre of its axis also. Compared to the classics this shaft section and tip are not visually eccentric. I will pull one out and check the measurments. It may be that the eccentricity of the cam is MUCH less but still required.

Also, does anyone have an HP41C card reader repair manual? The DVD set does not include one.

cheers, Geoff

Edited: 24 Feb 2010, 1:21 p.m.


Also, does anyone have an HP41C card reader repair manual? The DVD set does not include one.

cheers, Geoff

The 82104A card reader service manual is available on TOS, there is a section dedicated to "Motor installation and adjustment" on page 3-5.


Well, thanks everyone including Ignazio and Didier for pointing me to the correct reference in the manual.

There is an eccentric cam in the HP41C which it seemed everyone new about but me ;-).

I have modified the chapter to include the same procedures for aligning the cam to create the minimum current draw for the motor. This would be the correct position for the cam.

I have a white 67 cam and a black 41C cam in front of me now and the ( in my defence ;-) level of eccentricity of the 41C cam is much lower then the 67 version.

Cheers, Geoff


Hi, Raymond;

I tried a silicon tube once and after cutting a piece of it and assembling it, I noticed that its thickness was not regular, leaving a visible 'lump' that pressed the card a bit more while pulling it and causing many reading problems. After that I restored all card readers I could with o-rings, and the three ones I own work fine with them. Is it possible that I am using o-rings with such dimensions they fit correctly in place? I never noticed any problems with my card readers after using o-rings.


Luiz (Brazil)


Hi All,

Thanks for all your responses, and thanks for the great pics Geoff.

To answer your question Geoff, it's jerky when not in the card reader. I pulled the motor out, but left the power wires connected to the card reader circuit board, then inserted a card in the slot to turn the motor on, so the jerkiness is present with the motor unloaded. If it is the brushes, are these motor serviceable at all ?, they look like a sealed unit to me.

Also, I too believe that pinch roller axle shaft is assymetric, and I too don't like the O-ring repair, I prefer silicon hosing. I "true" it up by putting it on the gear, then mounting that on a shaft then spin it up on a dremel, and essential lathe it with an emery stick (those things that women used to smooth their finger nails). Silicon hosing is much more pliable than the hard rubber of the O-rings. Using silicon, I am sure there is different pressure applied to the nylon pinch roller as the roller axle is rotated.

Out of my spare motors, I only have one that is not jerky, so I'll give that a shot.



Obviously I will have to check some of 41C card readers!!!

Not a problem as I have two here that need new pinch rollers and both dated 1979 and 1980. I have yet to open the motor as all mine have worked smoothly. Other than cleaning the internal stator and brushes I don't know what or wear parts could be secured. I keep an eye out for absolutely recked machines for spares. And then swap the parts. That is how I found that the HP65 motor and worm gear will not work in an HP 41 C card reader due to the lenght of the assemblies.

Also, if you buy 'mil specification' fuel line hose, you will get the hole in the centre. I supplied everyone at the HCC2009 with 6 inches of this tubing and the hole is perfectly centred. No need for latheing.

I will dig up the roll (50 feet) and check the brand name. It seems this stuff is used by professional gas model airplane makers and military drones.

Cheers, Geoff

Edited: 24 Feb 2010, 7:34 p.m.


Hi Geoff,

That's interesting about the 65/41 card reader motor and roller gear not being interchangeable. Do you know if there is an level of "interoperability", i.e. between 65/67/97 and 41 ?. I am led to believe that the roller gears alone are interchangeable. Any more thoughts on that ? And what about the motors alone, i.e. without clutch and worm gear ??



The motor and shaft as well as the worm gear must be a specific length. I found this out the hard way by restoring a couple on a complete spare HP65 system. I then swapped out a bad 41C motor and worm gear for the HP65 system. I started to tighten the screws and noticed that the system was to long and forcing the screws would result in a jammed worm gear or the pressing out of the ball bearing at the tip of the worm gear.

Thats when I did the above measurements. Things in common appear to be the pinch roller, the nylon balls although the HP 41C has fewer and the nylon roller. The eccentric cams appear to be interchangeable but the HP41C eccentricity is much less then the classics (see above postings ;-)

I have to take apart the HP 67 to do a comparison and I am about to complete the topcat chapter at which time I will do more measurements. My inclination is that the Classic including the TopCat series will be the same but they will all differ from the HP 41C series. Of course there may be production differences between countries as HP shifted their manufacturing base.

Cheers, Geoff


...the nylon balls although the HP 41C has fewer...

Actually, the 82104A (HP-41C) card reader does not have any nylon balls, because it does not rely on them for the operation of the card sensor switches. Although I am not sure about this, I think it uses a reflected-light sensor. There is an LED inside the reader that I believe is used for this purpose. Perhaps Randy or someone else can correct/clarify/elaborate on this.


The I/R LED receiver and transmitter are the clipped card detector.

The motor run and card edge detector are done with the the two leaf spring switches.


to typing late at night from memory. And to boot this was part of the HCC2009 presentation (done correctly!)

Here I am writing a book, and then not refering to it! Not a very good advertisement. Here are some shots from chapter eight, the section dedicated to the HP 41C card reader!!!!

I really should think before I type:


I will endeavour to reference the material before typing at night from memory. My wife has told me my memory is lacking sometimes!!!!

Signed, a slightly embarrassed Geoff

Some more shots:

NYLON ROLLER AND BRONZE SPRING both also found in the classic and topcats

Nylon roller in place (no nylon balls):

The leaf spring switches Randy is refering to:

Edited: 26 Feb 2010, 1:50 p.m.


I think, the clutch can be repaired with shrinking tube. Would some lubricant help with the motor?


It's worth a shot Marcus, particularly if the motors can't be disassembled. Thanks for the suggestion.



Geoff is correct, the 65/67/topcat reader screws and housings are approximately 1 mm shorter than the 41 reader.

The motor itself, although they appear different in early models, are interchangeable between all readers.

With respect to jerky motion, before I suspect a bad motor, I'd look first at the coupler and then very carefully at all wiring and connections to same.

The 41 reader motors can be disassembled but getting the brushes back into place correctly involves careful study and sometimes just plain luck. The brush neutral position must also be set before gluing back together. The only real reason to open would be to lubricate but if you have the lead screw off, just set it on end and place a few drops of penetrating oil into the shaft area and allow to sit overnight. Repeat once then clean very well before re-attaching the screw.

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