Centroid M -400 help needed

[densman]

Hello I have a Dah-Lih knee mill with a Centroid M-400 3 axis control upgraded
to the linex system
Once last week , once yesterday and twice today, while running 4 different programs the machine would stop in mid program, the Z axis would start to retract in a feed type speed, then rapid in the z - . fortunetly the first time I was at the machine and able to mash the E stop.
After this happens when I try to jog the Z axis in either dirrection, in any mode(slow-rapid-incremental) it just takes off in rapid speed in the dirrection chosen and wont stop till it hits a limit switch or I hit the E stop
too get it back to normal I go into machine config screen and go in and out of the pid screen and plot screen while manualy rotating the z servo belt.
The last time it happened I was calm enough to notice what the message screen said; LIMIT SWITCH CLEARD
LIMIT:JOB CANCELED
EMERGENCY STOP
After I get it to opperate normally in jog mode I have to power down and restart and home the machine out
After this it will run normal (Z axis limit switches function normal when using tool check function or jog )
Any help with this problem would be welcomed
Dave Ensman

[racefast]

it sounds like you have a bad encoder on your z axis servo a way to test it is shut the machine down and swap the cable or cables to your servo so put z on x or y what ever is easier and vice versa power the machine up and jog what ever axis is on the z servo and see if it runs away also check the axis with the z cable on it if is fine and z runs away it is the encoder which is located in the end of the servo if z is fine and the other one is running away it is probaly the driver board you can also go into machine parameters and watch the encoder counts for each servo