Do an ohmic-contact test

Use this test to examine the resistance from the torch tip to the ohmic relay in the plasma cutting system. This test helps to find ohmic contact issues.

  1. Remove the power from the cutting system.
  2. Remove the top panel and the side panels from the TorchConnect™ console.
  3. Examine the J2 connector on the ohmic contact Printed Circuit Board (PCB).

    Make sure that the ohmic-relay coil is connected. Reconnect or tighten the ohmic-relay coil if necessary.

  4. Disconnect the ohmic-relay connector to get access to the bullet connector on the torch receptacle block-side inside of the TorchConnect console.

    To disconnect the ohmic-relay connector, unscrew and unplug it.

    This image shows the inside of the TorchConnect console, access to the bullet connector is available when the ohmic relay connector is disconnected.
  5. Use a digital multimeter to measure the resistance from the torch tip to the ohmic relay.
    A multimeter is measuring the resistance from the torch tip to the ohmic relay.
    1. If the resistance is infinite (open), replace the torch lead.
    2. If the resistance is less than 100 ohms (Ω), continue with the next step.
  6. Reconnect the ohmic-relay connector.
  7. Examine the ohmic contact PCB.

    Refer to Torch connect console ohmic PCB (141368) diagram.

    1. If the PCB configuration is for internal ohmic, make sure that the ohmic wire from the ohmic relay is connected to J3.
    2. If the PCB configuration is for external ohmic, make sure that the ohmic wire from the ohmic relay is connected to J4 pin 2 and that the ohmic wire from the lifter is connected to J4 pin 1.
    3. Adjust or tighten connections, if necessary, and continue with the next step.
  8. Supply power to the cutting system.
  9. Make sure that the torch does not touch the workpiece.
  10. Use a digital multimeter to look for 24 VDC between the workpiece, or chassis ground, and the torch tip (J3 or J4).
  11. If there is no 24 VDC, examine the wiring to the ohmic PCB.
    1. Make sure that the J3 or J4 connector is not clamped onto the wire insulation.
    2. Make sure that the connection between the J2 or J2A connector and the relay coil is good.
    3. Replace the relay if necessary.
  12. If you find 24 VDC, continue with these steps:
    1. Make sure that both the workpiece and the TorchConnect console are grounded in the same location.
    2. Touch the torch tip to the workpiece, or attach a jumper wire between the torch tip and the chassis ground.
    3. Examine the D2 Light Emitting Diode (LED) on the ohmic contact PCB.

      Refer to Torch connect console ohmic PCB (141368) diagram.

    4. Examine the D15 LED on the control PCB.

      Refer to Torch connect console control PCB (141334) diagram.

    5. Make sure that D2 and D15 both illuminate.
    6. If D2 and D15 both illuminate, make sure that the Computer Numerical Control (CNC) can receive ohmic contact signals from the cutting system or Torch Height Control (THC).

      If the CNC can receive ohmic contact signals, refer to the instruction manual for your CNC for troubleshooting recommendations.

    7. If D2 is not illuminated, replace the ohmic contact PCB.
    8. If D2 (on the ohmic contact PCB) is illuminated and D15 (on the control PCB) is not illuminated, examine the PCB wiring harnesses for loose wiring.
  13. If you cannot find or correct the problem, speak to your cutting machine supplier or regional Hypertherm® Technical Service team.