HP-65 Card Reader Problem Help

[Geoff Quickfall]

Sorry for tardy reply,

the speed is important and may be varied in the 67 and 97 with a variable resistor. The 65 has a soldered fixed resistor.

The problem is most likely the height of the pinch roller. This can be adjusted to release or apply pressure to the card as it passes over the read head. As the card pressure on the release head increases the current used by the motor increases. In the 97 manual it tells you the optimum current draw for the motor, hence the correct height of the pinch roller.

Without fancy oscilloscopes and etc. one can manage to hit the peak performance of the unit. I have had many card readers either read or write but not both, but with height adjustment of the pinch roller I have had success. The following assumptions are made, and they are not beyond reason:

- The resistor controlling the speed is good.
- all solder joints are good
- the wires to the reader are reinserted correctly
- the caps are good
- the "clutch" which is not a clutch but a vibration damper is good and the pinch roller material substitute is good.

What can go wrong? Well the material used to replace the pinch roller is probably slightly different in its OD. Logically, this is the difference as it is the only thing changed. That is, resistors don't die just because you looked at them. How to adjust the height? The axle with the slot holding the pinch roller in place is actually an eccentric cam. By rotating it through 360' degrees you raise and lower the pinch roller.

It is a matter of finding the sweet spot, either through the current draw method or the trial and effort method.

I repair all that can be physically; the dampening couple and the pinch roller, check all connections and solder joints. Then reassemble but leave the back off. I fashion a tool with a 90' bend in it ( one leg of pair of tweezers ) to access the slot and turn the eccentric cam. Run the card through to write a short program, switch to run and run the card through to read, adjust the cam, repeat, adjust, repeat...

Actually did this to Steves 67 at the 2014 meeting, I had to replace the o-rings someone had used to replace the pinch roller gummy wheel. The o-rings had hardened and were eroding on the surface causing his machine to read but not write, that is the pinch roller height due to erosion of the surface had reduced. I replaced this with the silicon tubing fix, adjusted the height and voila, done.

Geoff

Quick edit, Dave is correct, the speed is very important, my point is to attempt to adjust the pinch roller first before any components a swapped. Anecdotally I have varied the speed rather dramatically and still had successful read and writes. But there is a design sweet spot for the speed, and of course any card written must be readable by another machine, so a standardized speed is required.