Examine wires 420 and 422 for 24 Vdc on wires J10.1 and J10.3, respectively. Start the spindle and listen for a soft, audible click on the control board. If you hear this click (from a relay contact on the board), the machine control board is functioning properly. If you don't hear the click: Verify that there's 24 Vdc measured from wire 421 to wire 422. Make a jumper wire and, carefully,
momentarily jumper wires 422 and 420. If contactor K2 pulls in (you will hear an audible clunk) while you have the jumper on but drops out as soon as you remove the jumper, review the previous solutions to inspect why the K2 isn’t holding. If K2 stays powered on, the control board is not passing the run signal to the circuit. The control board passes 24 Vdc from wire 422 to 420 via a relay to create the start pulse. Measure wire 422 for 24 Vdc power. If present, the control board or wire 420 connected to J10.3 is defective. Power off the machine, and jumper J10.1 to J10.3 Power on the machine and check the VFD for a display. If the VFD reads rdy, the control board is defective. If not, wire 420 may be broken. Lift the connections of wire 420 at the control board and K2 and measure continuity.
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