Bad batch of cards, or reader/writer issue?

[GreyUser]

What we don’t know is if the cards were readable after writing in those other devices. If they were - then it is card deterioration or demagnetization.

It is doubtful it is the eccentric adjustment. With o-rings, the minimum force setting, where the pimple is towards the card surface (facing the front of calculator and the slot is parallel with the motor driven threaded shaft), is 99% of the time, the optimal position. If the force is too high, the usual result is for the motor to slow down under the load and the track write is not completed before the end of card switch is activated, throwing a write error.

[teenix]

Hi all,

I have a HP-41 card reader repair in progress so I decided to find out how the eccentric cam works as I couldn't see a reason for it to change its position when the shaft is turned.

The light of day has finally shone. On the end of the shaft is a small step that fits into the inner part of the card reader frame which is a smaller hole than the one the shaft pushes into. This small step is the part that has the offset for the shaft.

Its hard to see, but looking at the shaft in a horizontal position and the end with the screw slot to the right, the left end has the offset that fits into the hole on the inner part of the card reader frame.

In this position, if the screw slot is vertical and the little dot is toward you, then the eccentric shaft is at the low point meaning the shaft will raise up away from the card and the least pressure will be between the card and drive wheel.

On a 67, this means max pressure is when the screw slot is vertical and the dot is toward the motor and the least pressure is when the dot is toward the sense chip.

Mind you, I'm living in the land down under, so maybe I got that backwards.


I think this has been mentioned before, but some of the o-rings have small ridges on the outer radius due to remnants of the moulding process that makes them.

This material should be removed and sometimes the rings need to be reduced in diameter slightly more. If left as is they can push too hard against the little nylon idler wheel and would make the motor work harder than it should when passing a card. I push the o-rings onto a 9/64 drill, not on the flutes, but on the end that is gripped by the drill chuck. The drill can be put into the chuck and tightened with the o-rings about half inch below. Using the drill on not too fast a speed, a small flat file can be used to take the edge off. I think this should be continued with trial and error until the drive wheel is starting to move freely when the eccentric adjuster set for the least pressure - no card in the slot. This should allow for good grip with the extra card thickness added and you still have maximum adjustment if needed.

Care should be taken on final installation. If they are pressed too hard onto the shaft, they will squeeze up and the diameter will expand slightly.

cheers

Tony

[Massimo Gnerucci]

(08-10-2021 05:44 AM)teenix Wrote:  I have a HP-41 card reader repair in progress so I decided to find out how the eccentric cam works as I couldn't see a reason for it to change its position when the shaft is turned.

Thank you very much Tony, but may I stress that a (tagged) image is worth a thousand words? :)
I can easily miss or misunderstand some/many of the terms used...

Thanks again!

[teenix]

(08-10-2021 06:58 AM)Massimo Gnerucci Wrote:  Thank you very much Tony, but may I stress that a (tagged) image is worth a thousand words?
I can easily miss or misunderstand some/many of the terms used...

Thanks again!

I've been deleting old images to post new ones, so I added the info to the end of the Classic Notes PDF document.

http://teenix.org/ClassicNotes.pdf

cheers

Tony

[Massimo Gnerucci]

(08-10-2021 09:05 AM)teenix Wrote:  

(08-10-2021 06:58 AM)Massimo Gnerucci Wrote:  Thank you very much Tony, but may I stress that a (tagged) image is worth a thousand words?
I can easily miss or misunderstand some/many of the terms used...

Thanks again!

I've been deleting old images to post new ones, so I added the info to the end of the Classic Notes PDF document.

http://teenix.org/ClassicNotes.pdf

cheers

Tony

That's fantastic Tony!
Just downloaded the updated document.

Thanks.

[teenix]

Hi all,

Apologies if anyone downloaded the Classic Notes file, I had the eccentric shaft drawn upside down and some typos. I fixed these and added images relating to the eccentric shaft for the HP-41 and HP-97 card readers as well.

cheers

Tony