231-E1E0

Check STO Signal Wiring

Inspect X71 and X72 connector wiring on the PL 6xxxFS power module for loose connections, damaged conductors, or incorrect termination of STO.A.G and STOS.A.G signals.

Disconnect all power before inspecting safety circuit wiring

Verify Safety Relay Contacts

Use multimeter to check continuity of safety relay contacts in the STO circuit, ensuring proper switching of both STO.A.G and STOS.A.G signals during safety activation.

Check for voltage drop across safety contacts - should be <0.5V when closed

Test STO Circuit Functionality

Activate emergency stop and verify both STO signals change state properly using TNC diagnostic screens under MOD function key.

Monitor STO status in real-time through PLC program status display

Check Power Module Status LEDs

Examine status indicators on PL 6xxxFS module for fault conditions, particularly STO-related LED indicators that show safety circuit status.

Refer to power module label for LED status code meanings

Verify Module Supply Voltages

Measure 24VDC control supply and main power supply voltages to the power module, ensuring they meet specifications during STO activation.

Use proper PPE when measuring voltages on live circuits

Test STO Input Response

Force STO inputs active using external 24V source and monitor if power module responds correctly by shutting down inverter output.

Use oscilloscope to verify STO signal timing meets safety requirements

Replace Power Module

If hardware tests confirm internal failure, replace the PL 6xxxFS power module following Heidenhain replacement procedures and parameter backup/restore.

Ensure proper grounding and ESD protection during module replacement

Access SMP Configuration

Navigate to MOD function, select machine parameters, and access SMP safety configuration parameters for STO signal mapping and timing.

Document current parameter values before making changes

Verify STO Parameter Settings

Check parameters for X71/X72 control logic, STO.A.G signal polarity, and watchdog timing values against machine documentation.

Incorrect safety parameters can create unsafe conditions

Test Parameter Changes

After correcting SMP parameters, perform controlled STO activation test to verify proper power stage shutdown and alarm clearance.

Use TNC trace function to monitor parameter changes in real-time

Identify Safety Relay

Locate the safety relay in the electrical cabinet that controls STO.A.G and STOS.A.G signals to the power module.

Check electrical drawings for relay designation and contact configuration

Test Relay Response Time

Use oscilloscope to measure relay contact switching time when emergency stop is activated - should be within safety system timing requirements.

Verify relay is de-energized before testing contacts

Replace Safety Relay

If relay response is slow or contacts are welded, replace with identical safety-rated relay and verify proper wiring connections.

Test new relay operation before returning machine to service