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HP-65 card reader repair - can't write card, but can read
10-05-2016, 08:41 PM (This post was last modified: 11-12-2016 12:13 AM by jay.)
Post: #1
HP-65 card reader repair - can't write card, but can read
EDIT: turns out that it can read cards, but not write - see http://www.hpmuseum.org/forum/thread-698...l#pid64043

Hello,

I'm in the process of repairing an HP-65's card reader. I've replaced the gummy wheel and the motor to worm coupler. Thanks to Paul Berger, I have some cards I can use to test it.

The cards appear to be driven through properly when I insert them. I enter a program in W/PRGM mode, insert a card to write the program to it. The screen blanks while the card goes through the machine, and the calculator displays a steady "00 00". I switch the mode to RUN, and put the card in to read the program back. The screen blanks while the card is being read, then I get a flashing display, which I understand to mean that it couldn't read the card.

Any suggestions on what to check next?

Thanks again to Paul for sending me those cards!
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10-06-2016, 02:08 AM
Post: #2
RE: HP-65 card reader repair - can't read/write card
Google eccentric cam, 41c, 97, 67, 65 card readers.
  • Have you replaced the dampening couple rubber?
  • Have you altered the eccentric cam?

Geoff
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10-06-2016, 02:55 AM
Post: #3
RE: HP-65 card reader repair - can't read/write card
(10-06-2016 02:08 AM)Geoff Quickfall Wrote:  Google eccentric cam, 41c, 97, 67, 65 card readers.
  • Have you replaced the dampening couple rubber?
  • Have you altered the eccentric cam?

Geoff

Thanks for the reply, Geoff. I have tried adjusting the eccentric cam, and I have replaced the coupler.
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10-06-2016, 05:58 AM
Post: #4
RE: HP-65 card reader repair - can't read/write card
Okay!

Can you test the card in another hp65?

Did you check the current draw on the motor when adjusting the motor -or- did you try the hit and miss card read write then turn the eccentric. The second method is more time consuming. There may be a very narrow range of read and write on the eccentric adjustment.

Other factors, motor speed, magnetized head, dirty head, bad card.

Clear the program memory, run a blank card through to write a blank card. Then switch to run mode and insert the card. Still blinking?
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10-06-2016, 03:33 PM
Post: #5
RE: HP-65 card reader repair - can't read/write card
(10-06-2016 05:58 AM)Geoff Quickfall Wrote:  Okay!

Can you test the card in another hp65?

Did you check the current draw on the motor when adjusting the motor -or- did you try the hit and miss card read write then turn the eccentric. The second method is more time consuming. There may be a very narrow range of read and write on the eccentric adjustment.

Other factors, motor speed, magnetized head, dirty head, bad card.

Clear the program memory, run a blank card through to write a blank card. Then switch to run mode and insert the card. Still blinking?

I don't have another unit to test the card.

I tried both the current draw and the trial and error method, though admittedly my adjustment steps were quite coarse. I read that the ideal motor current with the card stalled is 180 +/- 20 mA, but couldn't get the current to go below ~320 mA in that condition. I get ~120 mA with no card, and ~220 mA while the card is running through. Does that indicate that I may have compressed the o-rings too much when installing them such that the OD is too large? What is the correct OD?

I just tried writing and reading a card after clearing the program memory, and I still get a blinking display.

Thanks for the help. Your insulation coupler tips were very helpful.
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11-12-2016, 12:10 AM (This post was last modified: 11-12-2016 12:12 AM by jay.)
Post: #6
RE: HP-65 card reader repair - can't write card
I've finally had the chance to play with the card reader again. I've found that it can read cards - I tried reading a card written in an HP 41, and it seems to read fine (no blinking, puts instructions in the program memory), though it of course can't execute the program.

I've tried carefully adjusting the eccentric cam a bit at a time, to no avail. What are the likely/possible causes of an HP-65 that reads cards, but doesn't write them?
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11-12-2016, 03:25 AM
Post: #7
RE: HP-65 card reader repair - can't write card, but can read
I finally got it working! It turns out that the card switches weren't making good contact with the PCB. Thanks for all the help!
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12-17-2018, 03:41 PM
Post: #8
RE: HP-65 card reader repair - can't write card, but can read
Oh Boy! I have this same problem and I am going to take a new look at those switches. I hope that's it. Thanks.
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