SRVO-037

Check external equipment status

Inspect all connected equipment, PLCs, and safety devices for active alarms, E-stop buttons pressed, safety gates open, light curtains blocked, or any fault indicators. Check operator panel displays and PLC HMI screens for fault messages.

Do not bypass or jumper safety devices. Resolve the actual safety condition before proceeding.

Verify PLC logic and outputs

Access the PLC program and monitor the output coil driving the *IMSTP signal to the robot. Verify the logic conditions required to enable this output are all satisfied. Check for latched fault bits or timers preventing the signal from activating.

Many integrators use a 'first fault capture' or alarm stack in the PLC. Check if an earlier transient fault is still latched even though the immediate condition cleared.

Monitor IMSTP signal status in real-time

On the teach pendant, navigate to MENU → I/O → Digital → Check the *IMSTP signal assignment (typically UI[1] or similar system input). Watch this signal while clearing external faults to confirm it changes state. Press [SHIFT]+[COORD] to view I/O in real-time diagnostic mode.

The *IMSTP signal should show ON (1) during normal operation. If it shows OFF (0), the external device is actively stopping the robot.

Clear the alarm after signal restoration

Once the external device resolves its fault and the *IMSTP signal shows active (ON) in the I/O diagnostics, press and hold RESET on the teach pendant for 2 seconds. The SRVO-037 alarm should clear if the signal remains stable.

If the alarm immediately returns after reset, the external signal is unstable or the fault condition is still present.

Identify IMSTP terminal location

Open the controller cabinet and locate the *IMSTP input terminal. On R-30iA/B controllers, check connector JD1A on the main CPU board (FANUC markings show *IMSTP, typically pin 17-18 on TB1 terminal block for older configurations). Consult the CONNECTION & SETUP manual for your specific controller model.

Lockout/tagout the robot system and discharge capacitors before opening the controller cabinet or touching terminals.

Inspect wiring and connectors

Visually inspect the wire connection at the terminal block. Check for loose screw terminals, pushed-out pins in connectors, broken wire strands, burn marks, or corrosion. Gently tug the wire to verify mechanical connection. Check continuity along the cable run from controller to external device.

Use a multimeter to measure continuity with power OFF. For active-high configurations, you should read 24VDC at the terminal when the external device is enabling the robot.

Verify signal at controller input

With power restored and the external device in 'run enable' state, measure voltage at the *IMSTP input terminal. Should read 24VDC for active-high or 0VDC for active-low configurations. Compare against the signal configuration in system parameter $IMSTP_CFG[1] (signal polarity setting).

If voltage is present at the terminal but the I/O diagnostic shows OFF, suspect controller input circuit failure or incorrect parameter configuration.

Reseat connectors and secure terminals

Power down the controller, disconnect and reconnect all connectors in the *IMSTP signal path. Clean any corroded contacts with electrical contact cleaner. Tighten terminal block screws to manufacturer torque specification (typically 0.5-0.6 N⋅m for signal terminals). Power up and retest.

After any wiring work, perform a complete safety circuit verification test before returning to production.

Check current IMSTP configuration

On the teach pendant, navigate to MENU → NEXT → SYSTEM → Variables. Search for system variable $IMSTP_PDSF or check I/O configuration under MENU → I/O → I/O Config. Verify whether *IMSTP is configured as active-high (signal ON = enabled) or active-low (signal OFF = enabled).

Standard Fanuc practice uses active-high for safety signals (24VDC present = safe to run), but custom integrations may vary. Check the electrical drawings.

Compare with external device output type

Determine if the external PLC or safety relay outputs a sourcing (PNP/active-high) or sinking (NPN/active-low) signal. Check the device specifications and wiring diagrams. Safety relays typically use normally-open contacts that close (conduct) when safe, providing 24VDC to the input.

If using safety relay with N.O. contacts wired to 24VDC source, the robot should be configured for active-high. If using N.C. contacts or sinking outputs, configure for active-low.

Adjust I/O signal configuration if needed

If polarity mismatch is confirmed, navigate to MENU → I/O → Config → Digital Input → locate the *IMSTP signal assignment. Modify the signal logic parameter to invert the input sense. This typically requires enabling 'Edit' mode and may need management-level password access.

Changing signal polarity on safety-rated inputs requires validation testing and documentation. Consult your facility's safety coordinator before making changes.