HP-65 Card Reader Problem Help

[Dave Frederickson]

(06-25-2015 11:20 PM)Phoenix Rob Wrote:  I have a copy of the manual. The manual has a procedure to measure the motor current when a card is inserted just far enough to start the motor (but not letting the card to pass). The manual has a spec of 180 mA, but I measure 80 mA with all positions of the eccentric cam.

I couldn't get this to work, either, but I think I understand what's going on. By holding onto the card and not letting it pass, this is making the motor work harder, causing an increase in current. Adjusting the eccentric cam varies the pressure on the card, varying the work the motor does, and causing a change in current. If the current doesn't change then it sounds like adjusting the cam is not having an effect on the friction between the card and the roller on the motor shaft.

At this point I'd try Geoff's technique. Just be sure to use a pre-recorded card for the test READs and a blank card for the WRITE's. The magnetic developer should also give a good indication when the proper speed is found. If your card reader uses fixed value resistors to adjust speed, consider replacing the resistor with a 10K trimpot.

As a last resort there are folks on the forum and eBay who'll repair the card reader for around $80.

Dave