HP-67 Card Reader became very touchy

[teenix]

(10-20-2023 12:09 AM)Alevin Wrote:  After reassembling, the light squeal some time was heard disappeared.
. . . .

May be the lo-batt condition reduces the card speed and these makes easier to read the card?

Regards

The squeal can sometimes be the lubricant at the end of the drive shaft has dried out and the shaft is rubbing against the ball bearing at the end. Some molybdenum grease can help, Tamiya brand in small tubes available at hobby stores.

It could also be caused by a damaged coupler causing the motor shaft to oscillate back and forth, or the bearings in the motor have worn.

Maybe the normal battery condition is causing the card to move too fast through the reader and the HP software cannot keep up with reading it. The only way to alter the speed is to change the motor speed resistor value on the sense board.

If you have an oscilloscope, you can check the read data and make sure it has completed before the motor switch opens. The bit width is approximately 1mS (1KHz).

There are some additional service notes for the card reader near the end of the HP-97 service manual.

cheers

Tony