Which resistance controls the card reader speed on a HP-97

[Kees Bouw]

Hi Francois,

What a coincidence! I also finished restoration of my HP-97 this weekend and I also could not get the card reader to work. The exact same problem as you describe: card runs through smoothly but always results in "Error". I removed resistor R1 and soldered wires so I could test resistor values outside the calculator. Unfortunately, it made no difference at all. The original resistor was 4.42K and I tried many values between 3K an 9K. The higher the value, the faster the card goes through. But the error was always there. I don't really know what to do next, I am still thinking about it. It is difficult to test because you can't see what is happening and you can't adjust the eccentric cam unless you take the calculator apart. I think the service technicians back in the day must have had special test equipment to fine tune the card reader outside of the calculator. Please let me know if changing the resistor works for you.

Kees.