loop "trembling of servomotor


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I have the next situation: one S7-300, one drive KDS1-100-300 and one piece of 3 phase permanent magnet motor MAC 112D. The PLC is controlling the motor to cut pipes. That configuration worked and now the motor start to trembling when I try to use man/aut. I found that the 0-10 V signal sent from the S7 was not very smooth and I changed the card, but the problem still exist.I used an external 0-10V and the same.

I observed that if send 0-10V to the drive, the motor start to tremble, I remove the voltage but the motor remains in that state of trembling. The PID loop remains blocked but I don't know how to find what equipment is in fault. I don't have the possibility to change the motor or the drive, or other to test on it.

Could be the tacho-generator from the motor the problem?
It is possible to use the motor on "direct"?? I mean to power direct from the lines and test at full speed, but I don't know if I can without the loop...

I don't know if I can "fool" the drive to run without the loop...

If you have motor's trembling with both man/auto modes, then possible trouble maybe mechanical issue. Than check all possible system's stiffness: motor's shaft to load, taxo to motor's shaft and between load's parts as well.
If you remove the analog signal you have to do a short-circuit on the the terminals? otherwise the input is "open" and very sensitive.