231-8A00

Access PLC Status Display

Press MOD key, navigate to Settings > PLC > Status. Monitor the PLC marker status in real-time, specifically looking for axis enable markers (typically M4xxx range depending on configuration).

Search for 'ENABLE' or 'RELEASE' strings in the PLC program using the PLC editor to quickly identify the controlling logic.

Check M-Function Outputs

Many machines require specific M-functions like M80 for all axes enable or M81-M89 for individual axes. Verify these are executed in the NC program startup sequence.

Verify Safety Input Conditions

Check MOD > Settings > PLC > Inputs to confirm all safety-related digital inputs (emergency stop chain, enabling switches, door interlocks) show correct logic states that permit axis enabling.

Do not bypass safety inputs permanently. Use only for diagnostic purposes and restore all safety functions immediately.

Test Manual PLC Marker Override

In the PLC Status display, attempt to manually set the axis enable marker to TRUE to verify if the inverter responds. If successful, the issue is in the PLC logic, not hardware.

This test immediately isolates PLC software from hardware issues - if manual marker setting enables the drive, focus troubleshooting on PLC program logic flow.

Check Digital Output Status in Diagnostics

Navigate to MOD > Service > Test > Digital Outputs. Identify the output number assigned to the affected axis enable (consult machine documentation). Attempt to manually toggle this output and observe the status indicator.

Output numbers for axis enables are typically in the lower range (Out 0-15) and configured in the machine configuration file under [DIGITAL_OUTPUT] section.

Measure Voltage at X11/X41 Connector

With control powered and enable commanded, measure DC voltage at the specific X11 or X41 pin assigned to the axis enable. Consult the TNC electrical documentation for pin assignments. Expect 24VDC when enabled.

Power is present at these connectors. Use appropriate PPE and ensure measurements do not short adjacent pins.

Inspect MC Board Output Fuses

Remove MC board and visually inspect output section fuses (typically small surface-mount or plug-in fuses near the X11/X41 connectors). Use continuity tester to verify fuse integrity.

On TNC 640, check F1-F4 fuses on the MC board. On iTNC 530, inspect the UEC board output section if external.

Replace MC Board if Output Defective

If output tests fail with good fuses, the MC board output stage is likely damaged. Replace the MC board and reconfigure using the backed-up TNCbackup file to restore all parameters.

Always create fresh backup before board replacement: MOD > System Files > TNCbackup > Start Backup to USB device.

Access Inverter Configuration Interface

Connect to the inverter using the appropriate interface (Heidenhain Axis Diagnostics Tool via Ethernet, or direct display if equipped). Navigate to the Enable Input Configuration section.

On newer TNC 640 systems, use integrated Service > Axis Diagnostics directly from the TNC rather than external tools.