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HP-41 Card Reader 82104A repair questions
12-30-2017, 02:34 AM (This post was last modified: 12-30-2017 02:37 AM by Craig Bladow.)
Post: #1
HP-41 Card Reader 82104A repair questions
I'm in the process of repairing two HP 82104a card readers for the HP-41. Thanks to the good instructions hosted in the repair section of this website, I'm well on the way to completing repairs.

Both Card Readers had the Gummy Wheel issue which is straightforward to fix.

After closing the first one up I got some "checksum" errors at first, but they stopped. What might cause that? I tested by using cards written by another card reader and by the the one just repaired with no difference in results.

Card reader number 2 was saved for last because it 'Rattled'. Good news is that this is due to a loose leaf spring, bad news is that the plastic Clip is broken so it can no longer hold the leaf spring in place, or properly clip into the 41. I suspect this will work, if care is taken not to move the carder around while in use. Other than finding a donor Card Reader with an unbroken clip, are there other ways to mend or work around the broken plastic clip?

Oh! And what is the function of the internal LED? I don't see a corresponding photo-detector.

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12-30-2017, 05:53 AM
Post: #2
RE: HP-41 Card Reader 82104A repair questions
Quote:Oh! And what is the function of the internal LED? I don't see a corresponding photo-detector.

You can find the Cardreader Repair manual at TOS where they discuss on page 3-6 the repair of the phototransistor. Earlier on they describe the various circuits and their functions. I believe it is used to detect a card being entered, but others might have better information.

hth.

Cheers,

PeterP
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12-30-2017, 08:39 AM (This post was last modified: 12-30-2017 08:40 AM by AndiGer.)
Post: #3
RE: HP-41 Card Reader 82104A repair questions
The LED inside is for detecting a clipped / non-clipped card (when writing).
How this really works I didn't care :-)
CHKSUM ERROR often derives from the card running too slow or too fast.
Did you trim the reader by turning the excentric cam?
Sometimes you have to fix the "clutch" as well.
Good luck
Andi
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12-30-2017, 07:49 PM
Post: #4
RE: HP-41 Card Reader 82104A repair questions
I did notice the tiny photo-detector when I was putting the second unit back together. The first one I repaired has settled down and works consistently. Using "VER" on a known good card in the second reader results in "MALFUNCTION", so I have some reading to do in the repair manual.

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12-31-2017, 04:54 AM
Post: #5
RE: HP-41 Card Reader 82104A repair questions
After measuring the motor current while feeding a card, which passed, I re-connected and mounted the motor/drive back into the reader shell. Now it works! The only thing I can think of is that I had a loose or transposed magnetic head wire.

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12-31-2017, 05:47 AM
Post: #6
RE: HP-41 Card Reader 82104A repair questions
(12-31-2017 04:54 AM)Craig Bladow Wrote:  After measuring the motor current while feeding a card, which passed, I re-connected and mounted the motor/drive back into the reader shell. Now it works! The only thing I can think of is that I had a loose or transposed magnetic head wire.

Congrats!!

Cheers,

PeterP
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01-01-2018, 11:27 PM
Post: #7
RE: HP-41 Card Reader 82104A repair questions
I re-attached the metal leaf spring to the plastic clip by using thick superglue. This held up through re-assembly so I am hopeful it will last.

I also had a 97 card reader that would read but not write cards, giving an "Error" for each attempt. It turns out the Write Protect Switch (WPS) contacts needed cleaning and adjusting. Works fine now!

Next in line is an HP-65 card reader. The calculator is in great shape and just needs the card reader fixed.

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01-02-2018, 07:56 PM
Post: #8
RE: HP-41 Card Reader 82104A repair questions
(01-01-2018 11:27 PM)Craig Bladow Wrote:  I re-attached the metal leaf spring to the plastic clip by using thick superglue. This held up through re-assembly so I am hopeful it will last.

I also had a 97 card reader that would read but not write cards, giving an "Error" for each attempt. It turns out the Write Protect Switch (WPS) contacts needed cleaning and adjusting. Works fine now!

Next in line is an HP-65 card reader. The calculator is in great shape and just needs the card reader fixed.

sounds like fun.
Wish I had the dexterity and patience to fix my own card reader issues.

.....Art
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