HP-65 more on the card reader

[wallyt]

I am having a somewhat similar problem with the HP65 card reader that I have been restoring. After cleaning the gunk out I used silcone tubing for the pinch roller and the reader transports the cards okay, but it does not seem to read or record. I tried all sorts of adjustments on the eccentric cam, no help. I measured the motor current and have been able to get it to 200mA by adjusting the cam. But the reader still does not read or record. When I attempt to read a card into the unit I get the same "endless loop" result that Alberto mentioned.

I got the idea the other day to give the sense amplifier a shot of freeze spray and then try the reader. WOW! It started to work fine. I was able to record a short program on a card, power cycled the unit, and read the card back in. Problem was that the good results were temporary, and I assume the area of the sense amp warmed back up.

I do not know if the sense amp was really faulty. The freeze spray also hit the adjacent fixed 5.11k ohm motor speed resistor and could have changed its value a bit. I decided to lift the resistor and replace it with a 10K pot pre-adjusted to 5.11K ohms. When I tried programming and reading a card back in the unit worked okay, but only for a couple of passes. I adjusted the pot slightly, up to about 5.8k and down to about 4.8k. I could hear the slight speed difference in the motor when feeding it a card. Unfortunately I could not reproduce the good results that I had earlier.

Very infrequently, when feeding a card I hear a screech from the unit. Today, I am going to repair the dampening "clutch". I don't know what else to try.