Low torque on DC servo motor.

We have been chasing a problem of x axis pulsing on a Lagun 3516 that we are putting back in service. We found that when the servos are powered up you can push the table and rotate the motor. It has SEM dc motors and a Glentek servo amp and we already swapped the axis cards with no improvement. This machine does have Heidenhan scales rather then encoders. I am not sure if it is a feedback problem or a motor problem. I was going to swap the motor but they do not suggest low torque as a motor problem. Any ideas?
Thanks in advance.

Hi,
A couple of things come to mind. Grab a battery box: often a 9V battery with a pot (adjustable resistor) and a switch to reverse polarity. Lift the input to the servo amp and attach battery box. The full 9 V should give you 90% of rapids. Use reverse switch to test both directions. Make sure you start with the bed in the middle of travel so you avoid surprises. :-)
May I have this reversed. Disconnect the servo motor leads from the servo amp. Connect to 12 V dc , 24 is better if you have it. Your SEM's should have a label that says something like volts/1000 rpm. -33, etc. Again reverse polarity to prove bidirectionality.
Just for grins; try to move a given distance under battery power and see is the scale agrees.
That should get you started.
Good luck. Troubleshooting is so much fun. ;-)

p.s.
Obviously you can use just a 9V or smaller battery and a couple of leads but the battery box is handy to have around.