Fanuc 3m tachogenerator/spindle problem

[SSMrob]

Spindle won't go over about 4k...

Load goes into red when I try over 4k, and it makes a jittering noise.

RPM meter seems to read wrong..

How do I check tachogenerator output into spindle motor controller ie what pin/signal at control board?

Also, could this be bad brushes? Bad pickup brushes for tachogenerator? foreign material/metal chips in motor? bad parameters in controller?

Thanks in advance!!!

[Al_The_Man]

Last one I had with this problem turned out to be the Tach.
It seemed to be putting out voltage ok, but a replacement solved the problem.
It would not hurt to check the main brushes anyway.
The DC tach is right on the back end of the motor and outputs 20v/1k rpm.
Al.

[cncdiag]

To tell you the check pin for tach feedback it would help to know the part number of the drive.