330-0008

Verify E-STOP and safety circuit status

Check that all emergency stop buttons are released and safety interlocks (doors, light curtains) are in safe closed state. Verify safety relay contactors have pulled in.

Do not bypass safety circuits. Use proper lockout/tagout procedures when checking safety components.

Check inverter enable signal at X120 connector

Measure voltage at X120 pin for inverter enable (typically pin assignment varies by PSU model - consult electrical diagrams). Should show 24VDC when safety chain is closed.

On UM and EM PSU units, check the green 'Enable' LED on the inverter module - it should be lit when enable signal is present.

Test safety relay outputs

Use multimeter to verify safety relay outputs feeding inverter enable are switching properly. Check for welded contacts or coil failures in safety relays.

Listen for audible 'click' when powering up - safety relays should energize. Absence of click indicates relay or power supply issue.

Measure DC bus voltage

Access MOD > Diagnosis > Inverter and check DC link voltage display. For 3x400VAC input, expect 540-590 VDC. For 3x480VAC input, expect 650-700 VDC. Voltage below 500 VDC indicates precharge or rectifier issue.

High voltage present on DC bus terminals. Only qualified personnel should measure DC bus voltage directly.

Verify three-phase input voltage

Measure all three incoming phases (L1, L2, L3) at inverter input terminals. Check for balanced voltages within 5% and correct phase rotation. Missing phase will prevent proper DC bus voltage.

Use the control's built-in diagnostics: MOD > Diagnosis shows input voltages on most TNC models. Compare displayed values to physical measurements.

Check precharge circuit components

Inspect precharge relay and precharge resistors in PSU for signs of failure (burn marks, open circuit). Precharge relay should energize after initial charge cycle, bypassing resistors. Failed precharge components prevent DC bus from reaching operating voltage.

Precharge resistors typically fail open after repeated thermal cycling. If DC bus voltage rises slowly then drops, suspect precharge relay not closing.

Check inverter module LED indicators

Inspect the LED status indicators on the PSU/inverter module front panel. Green LED indicates ready, red indicates fault. Refer to PSU manual for specific LED blink code patterns that indicate fault type.

UM 1xx and EM PSU modules have diagnostic LEDs. Count blink patterns - e.g., 3 blinks may indicate overcurrent, 5 blinks temperature fault. Document pattern for Heidenhain service.

Review inverter fault history

Access MOD > Diagnosis > Inverter Fault Log (if available on your TNC model) to check for recorded inverter faults. Look for overcurrent, overvoltage, or thermal faults preceding this alarm.

On iTNC 530 and TNC 640, use MOD function > PLC > System Messages to view detailed inverter status words and fault bits.

Perform inverter module power cycle test

Disconnect power from machine, wait 5 minutes for DC bus discharge, then reapply power. Observe if inverter module completes initialization sequence. If alarm persists immediately, inverter module likely has internal hardware fault requiring replacement.

Wait minimum 5 minutes after power-off before accessing components. Verify DC bus voltage is below 40 VDC before touching terminals.

Check inverter cooling system

Verify cooling fan operation on inverter module and check air filter cleanliness. Blocked airflow causes thermal shutdown. Confirm fan spins freely and draws proper current (typically 0.2-0.5A for 24VDC fans).

Inverter thermal sensors may prevent ready state even before overtemperature alarm occurs. Feel heatsink temperature - should be warm but touchable during normal operation.