That is normal for a stepping motor. When energized it is stationary but a firm hand can still turn it. As you turn it you can feel the poles of the motor.
When OFF, it turns a lot easier but you can still feel the poles of the motor. On a new motor the poles are stronger. On a old motor the poles are weaker. Thus a old motor cannot accelerate as well, the current does not drop as far at rapid (another way of knowing the health of the motor), and the motor will stall easier under load.
Read up on stepping motor theory.
Have you checked voltage and current?
George
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(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
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