HP 67 Circuit Board

[teenix]

Unscrew the motor and remove it from the plastic Mount.

Try the turn the drive roller manually. It should spin very easily. If the replacement "rubber" part is too wide or the diameter is too large it can rub on the plastic surrounds. It should be relatively easy to check for roundness too.

A larger than normal diameter can also cause excess pressure to be placed between it, the card and the little nylon roller that supports the card under the drive wheel even when the drive pin is adjusted for maximum clearance. All these effects can slow the mechanism and greatly load the motor and the sense chip motor driver. Some of this is explained in the Classic Notes starting at page 34.

If the sense chip is getting hot during the motor testing then there is a problem somewhere and will most likely lead to some (possibly expensive) failure.

If the sense chip is heating up, maybe it goes into "hot tempered and cranky mode" and won't work until it has cooled a bit. I don't know if it has overload protection built in like more modern drivers.

Have you replaced the missing screw. If not, maybe the motor is offset a bit from its normal center line.

cheers

Tony