Limit switch problem?

[Bill Gillen]

Hi,

I recently got a DoAll mill with an older Centroid M40 3-axis control. When I try to home it, I get a 411 message _axis full power without motion. If I turn off the bottom Z (-) limit switch via the DIP switch, then everything works fine. It will home, run programs and do everything I ask. I ohmed the switch, and it seems to be fine and working. I then checked wiring, and there does not seem to be any shorts or opens. It had the right voltage (+5VDC). If I turn it back on (via the DIP switch), the above mentioned problems come back.

Any ideas on a fix?

Thank you,
Bill Gillen

[cncsnw]

You probably have a loose connection in the cabinet, either at the PLC or the servo drive. If the switch itself were faulty, you would get false "407 Z- limit (#?) tripped" messages. Since you only get "411 Z axis full power w/o motion", then the switch is remaining closed as far as the PLC can tell, but the servo drive thinks the switch is open.

Is this a 1993-1994 M40, with the flat 15/15 PLC board, or a 1994-1996 model with the RTK2 PLC unit (stack of three boards)?

Try cleaning (with contact cleaner) and reseating the 8-pin Waldom plug where the limit switches plug into the servo drive, and, if you have an RTK2, do the same for the 10-pin Waldom plug on top of the RTK2.

See http://www.cncsnw.com/ServoLogicPM.htm for an illustration of where the limit switches connect from the RTK2 to the servo drive.

[Bill Gillen]

Thank you cncsnw. I really appreciate the help. I followed the instructions on your Centroid DC Servo Drive Preventive Maintenance page, and it works like a charm now. Also, I have experienced the jerky movement twice before (and broke some bits), and was wondering what I did wrong. Now I can see what happened.

Again, thank you very much for your help.

Bill Gillen