Re: HP67 motor in HP65 card reader - too slow - Solved Message #4 Posted by Randy on 20 May 2012, 7:43 p.m., in response to message #3 by Harald
FWIW, I have disassembled both types of motors and the only difference I noted was the ability of the later motors to have the brush neutral position adjusted as part of the manufacturing process and then having that point locked into place. This lowered the overall operating current, sometimes as much as 20 ma.
The original HP65 motors with the red, molded in place brush holder were not adjustable, they were just molded into a fixed, coarse adjustment position. As a result, the operating current had a much higher variation from motor to motor. This no doubt let to differences in speed as the motor was used at much lower voltage levels than it was designed for, most likely in the 10 to 15 volt range. The card readers ran them at an average of 3 volts. These variations, along with the variation in capacitor values in the sense amp die, necessitated the need for the "trimming" resistor to properly set the motor speed for the application.
Edited: 20 May 2012, 7:46 p.m.
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