HP-67: Unreliable card reader fixed

[Marcel Samek]

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.

[HP67]

Great news. The world needs more 67s!

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