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Full Version: HP-67: Unreliable card reader fixed
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Wanted to post my experience so that someone in the future may benefit:

Since I bought it, my HP-67 has had problems with the reader. It was able to read pre-recorded cards very reliably. Never a single problem with those. It appeared to record cards OK (never gave an error) but I only have one HP-67 so I was not able to verify whether those cards were actually recorded OK. However, when it came to reading cards that I had recorded, it was very flaky. It would give an error approximately 75% of the time.

When I bought it, the seller stated that the reader had been recently rebuilt and the wheels replaced, so I knew it wasn't the gummy wheel problem.

At one time I thought that the battery level impacted the problem, but I could not achieve consistent results no matter what I tried. Sometimes it would work but rarely twice in a row.

Yesterday I took it apart and inspected all the pieces. There was no residue and all the pieces looked in place. Just to be safe I cleaned everything with 99.9% isopropyl. Still no luck - same behavior as before.

Then, based on some posts I had seen on similar but not identical problems, I decided to play with the adjustable pot next to the reader's motor. I turned it an 8th of a turn clockwise. Now the reader was not able to read pre-recorded cards. I turned it an 8th of a turn counter-clockwise from its original position and magically the reader was able to both read and record cards.

I reassembled the calculator and read/wrote many cards both on battery power and plugged into the charger and everything seems rock solid.

I am guessing that whoever rebuilt the reader needed to adjust the motor speed with the POT to account for the slightly different wheel size and they did not do so properly.
Great news. The world needs more 67s!

They're still perfectly useful over thirty years after they were first created.
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