HP-67 - 1612A03018 - Card Reader Advice Requested (was HP-67 - strange behavior)

[teenix]

Running from the battery does not provide any speed regulation, it will run as fast as the power available lets it.

The card reader has speed regulation built in so as to compensate for fluctuating battery voltages during normal operation.

This is controlled by the 4K64 resistor. Have you tried testing the value of this part?

Putting a 10K variable resistor may help. I am not sure if the speed input to card reader chip can handle directly to ground or battery so may be wise to keep the variable resistor set around mid way.

Also, I have heard replacing the 6uF power filter capacitor with a tantalum one can enhance the motor operation. The small cap on the motor terminals might also be a problem. I think it also is part of the control circuitry for speed feedback, or maybe just for filtering.

The 67/97 card read/write can deal with slow or fast cards up to a point. As long as the data fits on the card within its limits it should work. The 65 is different as the data transfers have to be sync'd to the CPU but may still work with different card speeds, but again, up to a point.

cheers

Tony

cheers

Tony