Ok, so My 4th axis has been sitting for about a year. I have a Matsuura 1000 machine. Now when I rotate the rotary table, it gets a jittery spot at one specific spot at each revolution. I took the brushes out, and cleaned the armature of the servo motor with some scotch brite, and cleaned out any residue. The brushes also look real good, and new. I do not see any arced spots on the armeture/comantator. I checked continuity on all of the slits of the armature where the brushes ride, and that all checks out. I checked the encoder, and seems to be ok. But at one specific spot in the motor revolution, it goes back and forth really fast, like it doesnt know to go forward or backwards, and if you let it do that for a few seconds it will Error out and shut the servos down on the whole machine. WHen it is "jittering", if you try and lock the 4th axis also, it will overload the servo and shut the machine down. I am not sure where else to look, or what to do, any suggestions?