|Re: HP65 card reader problem|
Message #5 Posted by Matthew Riehl on 8 Sept 2000, 11:13 p.m.,
in response to message #1 by John Robinson
I have had two calculators where I needed to adjust the fingers. I visually determined which ones need to be adjusted.
You do this by disassembling the calculator. Remove the CPU circuit board from the center sandwich. You should then be able lift the keyboard Printed Circiut Board (PCB) from the plastic middle part.
When no cards are inserted into the slot all four of the long fingers are retracted back into the shallow recess. As the card goes progressively further into the slot, all four of the fingers reaches up sequentially to contact the bottom side of the keyboard PCB.
To determine which one needs to be adjusted hold the plastic center so that you can just sight along the top edge without seeing into the recess (you are looking across the top of it). Have the top edge of the calculator to your right.
As you put the card in it will hit the first small plastic ball which pushes up the motor run finger. You must see this finger come up out of the recess to where it would contact the bottom side of the keyboard PCB (if it were all put together). If this finger (I believe that it is the closest one to the top edge) doesn't come out of the recess, then that is why your motor isn't running. If it does come out, then the problem is elsewhere.
As the card is pushed completely through by finger pressure you should see all four of the fingers come up. In the order that they come up they do the following things: 1) start the motor, 2) tells the calculator that the card is up to speed and starts the read/write circuitry (depending on the WPRGM/RUM switch position), 3) senses the leading edge of the card and polls the fourth switch which, 4) senses whether the corner of the card has been cut off for write protection.
My first HP-65 had a problem where it either wouldn't read or write cards. I had blank cards but no pre-recorded ones so I could tell which problem it was. A kind gentleman sent me a card with a program already on it. That read OK so I knew it was a "write" problem. Upon doing the above procedure I found out that the third finger wasn't coming out of the recess. Hence since it never saw the leading edge of the card it never polled for the cut off corner. Without a "I'm not cutoff reply" from the fourth switch the calculator didn't write to the cards. It has worked like a champ ever since I adjusted this switch.
Remember, if the finger doesn't come out of the recess it could have two causes. First would be that the finger needs adjustment. Second could be that the little plastic ball that the card pushed up is gone. If this is the case, no amount of adjusting the finger will help.
There is a good article on this website about the card reader design < http://www.hpmuseum.org/journals/65crd.htm>. There is also a picture of the fingers <http://www.hpmuseum.org/65crdrbk.jp>. These should give you a better understanding.
Hope this helped. I just bought a scanner and have an HP-67 that needs repair, so maybe I'll be able to document this in the future.