Re: HP67 - Card Reader Problems



#5

Yes, the problem you describe is a disintegrating drive wheel. Even though your 67 has been taken care of, the rubber breaks down with age and becomes gooey (or sticky).

Using the article Warren is referring to (Steve Loboyko's "How to Fix Classic Models"), I just replaced my first 67 card reader drive wheel last week. I varied from his instructions by using two rubber O-rings instead of the fuel line tubing he suggests. You might have trouble finding the same O-rings in Germany (1/4 inch Outside Diameter by 1/8 inch Inside Diameter which means 1/16 inch thickness).

The only problem I found in Steve's procedure was the abscence of any description of removing the Pin which holds the drive wheel/worm gear in the plastic frame (where the motor mounts). This pin "appears" to be a plastic slotted screw head that "looks" like you should turn to unthread it, but it is actually a pin that needs to be pulled to free the drive wheel/worm gear from the frame.

For a better feel of what I'm talking about, first look at this photo of a completed HP41 card reader (similar to a 67 CR) repair with O-rings, http://www.hpmuseum.org/guest/card/cr5.jpg . Notice what appears to be a slotted screw under the black and red wires. This is the pin that must be pulled to remove the drive wheel/worm gear, as shown in this photo, http://www.hpmuseum.org/guest/card/cr4.jpg . These photos can be found in the article "Repairing the HP 82104A Card Reader" at http://www.hpmuseum.org/repair.htm .

As other people have said, accessing the two screws under the back label of the calculator will be the most painful part of the job, because you have to disturb the label to remove it (especially painful on a good condition calculator). And it never looks original when you put it back on (with rubber cement). I used a hair dryer to loosen the adhesive and a long flat knife blade to lift the label without creasing it. Sorry this message is so long.

Good luck,
Matt


#6

something about the tiny plastic bolt with a slot that 'looks like a screw':
actually, you do adjust the pinch roller pressure with it. you can either achieve quite a strong 'pull' on the cards or, reduce mechanical wear on the driving parts as far as possible and still maintain proper card intake.

after reassambling is done, test the drive with a card. then, turn the bolt a quarter turn in one direction and repeat the test. if the pickup is stronger now, you might turn the bolt 1/2 into the opposite direction and test again. if it is still too strong, just give it another quarter turn into the same direction. just keep in mind: one full turn into any direction will travel through all possible adjustments, so there is no difference in effect between one full turn and two full turns.
cheers, hans

#7

Comment on this statement:
"The only problem I found in Steve's procedure was the abscence of any description of removing the Pin which holds the drive wheel/worm gear in the
plastic frame (where the motor mounts). This pin "appears" to be a plastic slotted screw head that "looks" like you should turn to unthread it, but it is
actually a pin that needs to be pulled to free the drive wheel/worm gear from the frame."


This is more than just a shaft. This shaft has a slot because it is used to adjust the pressure on the drive wheel. I have seen readers NOT work, if this is not properly adjusted. Also, this adjustment may be more or less required, depending on the material that you use for the wheel.

#8

Thanks for the info on adjusting the drive wheel pressure by turning the pin. How come I didn't see this anywhere else (until you guys commented on this detail)? I'm curious, is this documented anywhere, or was the slot a giveaway (as it's a common adjusting device to you mechanical folks)? In order for the pin/shaft to vary drive wheel pressure, it must be eccentric (non-symetrical), right?

I need to correct my previous statement where I used the term "drive wheel/worm gear". I was trying to indicate the assembly that consists of the drive wheel and driven gear that are mounted on the same shaft. This driven gear is technically a "helical" gear, as the teeth are at an angle to it's axis (vs. a "spur" gear where the teeth are parallel to it's axis), and it meshes with the actual worm gear.

The "worm gear" itself is the straight, spiraling gear that is part of (and parallel to) the motor shaft assembly.

I must have been lucky because my card reader works even though I didn't know about making this pressure adjustment.

Thanks again,
Matt


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