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HP Forum Archive 19

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Card reader pinch roller dimensions?
Message #1 Posted by GanjaTron on 5 Feb 2009, 7:24 a.m.

Hi folks,

still trying to fix my HP-65's card reader (and one from an HP-97, for that matter). I bought 6mm silicone tubing which seems to fit nicely, but it doesn't pull the card through. Looks like it's fractions of a milli too small!

Can anyone here give me the *exact* diameter of the original pinch roller wheel? While we're at it, anyone happen to have the same for the TI-59's card reader (also awaiting repair)?

Thanks for the info,


Re: Card reader pinch roller dimensions?
Message #2 Posted by Rainer Wiedemann (Germany) on 5 Feb 2009, 5:24 p.m.,
in response to message #1 by GanjaTron

Hi Roland,

I never fixed a HP-65 card reader yet, but a bunch of HP-41 readers. IMHO considering the pinch roller the differences are not that big between HP-41 and HP-65 reader. The silicon tubing has always worked perfect for me, so I suppose a problem with either the motor clutch or it's simply a matter of adjustment.

Try to watch the worm gear and pinch roller gear. Do they continuously keep spinning or do they stop while the motor continues turning. This would point at the motor clutch as root cause. Remove the motor, apply some 2.5 volts to it and try to stop the worm gear with your fingers. If this is easily possible you should have gotten it. The clutch is attached to the motor side end of the worm gear. In the articles forum you'll find instructions how to fix it, some suggest a simple fix with magic glue.

If the clutch turns out to be ok and the card stops while pinch roller and worm gear keep spinning, then you will have to adjust the pinch roller pressure to the card.

The axle of the pinch roller is excentric. By turning it the pinch roller's distance and therefore its pressure towards the card can be altered. Do not make the pressure too high, the card should be pulled through without the motor getting throttled down much or making strange noises. The adjustment procedure is much easier operating the motor from an external 2.5 volts supply outside the calculator. So you don't depend on your batteries' state.

Would be nice to hear from you posting a message when you got it to work.



Re: Card reader pinch roller dimensions?
Message #3 Posted by GanjaTron on 10 Feb 2009, 12:29 p.m.,
in response to message #2 by Rainer Wiedemann (Germany)

Hi Rainer,

thanks for the hints, the clutch seemed to be the primary problem. I fixed it with superglue. One thing to watch out for is that you don't stick the shaft to the motor housing (I hooked the motor up to a lab power supply and let it spin slowly as the glue hardenend, just to make sure).

I got the pinch roller to work after applying a layer of vinyl tape on the roller's metal axle (cut to proper length to avoid over/underlap) before shoving the silicone tube over it while stretching it with a pair of tweezers. The extra 0.2mm (or whatever) was apparently enough to generate enough friction, and I didn't need any glue for the tube.

The eccentric slotted axle didn't even need any adjustment on my card reader (thank god, considering it's barely accessible on the HP-65). Remarkably, it could read & write straight away!

Now I hope this procedure's gonna work on the HP-97 too...



Edited: 10 Feb 2009, 12:31 p.m.

Re: Card reader pinch roller dimensions?
Message #4 Posted by Randy on 7 Feb 2009, 4:16 p.m.,
in response to message #1 by GanjaTron

Final diameter mounted on the gear should be 6.35mm. The tubing that works here in the US is 7/32" (5.5mm) with an 0.063" (1.6mm) wall thickness.

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