Gross Positioning Error

[Shanghyd]

I have a bridgeport intgeract II. I'm getting a gross positioning error lately.
The z axis servo will buzz and the gear will shake back and forth. Then the machine will quit with that error.
Resistance in the z axis servo is low compared to the y axis.
I've taken off the servo and cleaned the carbon deposits from the housing. I checked the brushes and they seem okay. Still plenty of brush left on all 4.
The commutator had a groove where the brushes run. I couldnt get a good idea of how deep the groove was but I could see a groove. I didn't pull the armature all the way out.

Any suggestions about troubleshooting this servo?
The machine is working fine right now but can error out at any time.

[gus]

likely a tach error, have you adjusted the trailing error?

[machintek]

Is there a letter after the gross positioning error?

George

[Shanghyd]

The letter was either a B or 8. My monitor is blurry sometimes.

The problem got worse. The machine errored out and the electrical box started smoking. I found a large black burned spot on the driver board. Now the z axis just dives towards the table and stops when it reaches its travel limit.
I either need a new driver board for the z axis or try to replace the bad components.