Foot switch of the chuck sometimes fail

Problem: Recently the foot switch of the chuck fail sometimes, turn on the power of the CNC lathe, input M12, M13 under MDI mode, the chuck works but sometimes not. From http://www.CNCmakers.com

Diagnose: it could be several reasons:

1-      There is poor contact of the foot switch or wirings.

2-      Check the control relay’s condition.

3-      The electromagnetic valve has problem or not?

4-      Any problem of CNC controller I/O ports? Input chuck clamp/chuck loose codes and see if the CNC controller signals are in effect or not, in this case we found that there are different signals, so it is external output problem, after check carefully, the chuck clamp relay has no output signal, change it and then everything is fine.