HP-67 Card Reader Repair Question



#3

What would cause the motor to slowly rotate in the direction of reading a card?


Edited: 7 Aug 2013, 10:51 p.m.


#4

The most logical source of trouble would be a fault in the sense amplifier. Pin 17 of the amp goes low to run the motor, this is controlled by the CRC. If that pin is not at the level of either rail, I suppose that could cause motor creep but that's speculation as I don't know what the circuitry is inside the sense amp.

BTW, if you replace the amp, don't forget to take the timing resistor with it, otherwise motor speed will most likely be wrong. If you have a later 67 with a pot, measure the resistance of the timing resistor in the device where you get the sense amp then set the pot in your 67 to that resistance.


Edited: 8 Aug 2013, 11:18 a.m.


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