HP-41 Card Reader 82104A repair questions

[Craig Bladow]

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.