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There is no speed control on this motor. It is controlled by the voltage regulator board. It uses a couple of error amp transistors to control current through a transistor. There is an error adjustment on the board, but it must be all the way at one end to even get close to the right output voltage. I suspect there may be a problem with the error amp transistors, but I can't really rule out the motor itself. The board uses a 10 volt supply and it should supply 3.64 volts to the motor. This all checks out with the motor disconnected. As soon as I connect the motor it drags the supply voltage down to less than 6 volts supply and under 3 volts to the motor. If the motor is not the issue, and it may not be, the regulator should see the error and allow the pass transistor to conduct more to make up for the voltage drop. However with the 10 volt supply pulled down so much I don't think it can supply enough current to keep the output voltage at 3.64 volts.
I did disassemble the motor and I noticed a disc capacitor inside. I wonder if it could be leaking? I may revisit this if I can't find a motor.
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