The most likely problem is the limit switch for the Y axis. The sequence for homing the axis after the operator initiates is:
- Axis feeds at rapid until the home switch plunger engages. The switch is normally closed so switch engagement opens the switch.
- Axis slows to a creep until the home switch closes again after passing completely over the tab mounted to the base.
- Control looks for home pulse on the encoder.
Thus, the control needs to see the switch go from closed to open to closed again, then looks at the encoder.
So if the switch is stuck closed (plunger sticking fully out of the switch housing), then the control never sees the home switch changing from closed to open to closed again. If the switch is stuck open (plunger fully depressed into housing), the control thinks the axis is already engaged to the tab on the base and feeds until the switch closes again before looking for the encoder pulse.
It is possible with the switch on that machine for the plunger visible on the outside to be working properly but the microswitch inside the housing to be sticking.