231-E1A0

Check safety relay status

Navigate to MOD > DIAGNOSIS > MACHINE > I/O and verify the status of safety relay inputs X121.17 and X121.18 (-STO.A.G signals).

These signals should show LOW (inactive) when safety circuit is closed

Measure relay coil voltage

Use multimeter to verify 24VDC supply to safety relay coil and check for proper switching operation when E-stop is cycled.

Ensure machine is in safe state before measuring voltages

Test relay contacts

With power off, use ohmmeter to test continuity of safety relay NO/NC contacts and verify they switch properly when relay is energized/de-energized.

Replace safety relay

If relay shows signs of contact welding or coil failure, replace with identical part number and re-test STO circuit operation.

Check cable connections

Inspect X121 connector pins 17 and 18 for loose connections, corrosion, or damaged pins. Verify proper seating of connector.

Use contact cleaner and dielectric grease on connector pins

Measure signal continuity

With power off, use ohmmeter to verify continuity from safety relay output contacts to TNC X121.17/18 inputs through the entire cable run.

Check for cable damage

Inspect STO signal cables for physical damage, especially in cable chains or areas subject to movement. Look for pinched, cut, or abraded wires.

Verify signal voltage levels

With power on and safety circuit closed, measure voltage at X121.17/18 - should be 0V (LOW). With E-stop active, should be 24V (HIGH).

Check input card LEDs

Observe LED indicators on the digital input card handling X121 signals. LEDs should correspond to actual signal states from safety relay.

Compare LED status with multimeter readings at connector pins

Test adjacent inputs

Check if other inputs on the same card (X121.16, X121.19, etc.) are functioning properly to isolate if entire card or specific channels are faulty.

Swap input assignments

Temporarily reassign -STO.A.G signals to unused inputs via MP7300 (Digital inputs assignment) to test if specific input channels are defective.

Replace input card

If input card shows signs of failure, replace with identical part number and reconfigure input assignments in machine parameters.

Verify STO input assignment

Check MP7300 series parameters to confirm -STO.A.G signals are correctly assigned to X121.17 and X121.18 inputs.

Document current settings before making changes

Check safety function parameters

Navigate to MOD > MACHINE PARAMETERS and verify MP1400-MP1420 (Safety relay monitoring) settings match machine wiring configuration.

Validate signal polarity

Confirm MP7310-MP7320 input polarity settings match the actual logic levels expected from safety relay (normally LOW when safe).

Reset to factory defaults

If parameters appear corrupted, restore safety-related parameters from backup or reset to factory defaults and reconfigure per machine documentation.

Measure 24VDC supply

Use multimeter to verify 24VDC ±10% at safety relay coil and TNC input common terminals under load conditions.

Check voltage during machine operation when current draw is highest

Check power supply loading

Verify 24VDC power supply is not overloaded by measuring total current draw and comparing to supply rating.

Test voltage stability

Monitor 24VDC supply with oscilloscope during machine cycling to detect voltage drops, spikes, or noise that could affect safety circuit operation.