SRVO-069

Identify the affected axis

From the teach pendant, press MENU → ALARM → F5 [DETAIL]. Note the axis number associated with SRVO-069. Check the alarm log (MENU → ALARM → F2 [HIST LOG]) to determine if the alarm occurs on a specific axis consistently or multiple axes.

If the alarm appears on multiple axes simultaneously, suspect a common mode issue like cabinet grounding or power quality rather than individual cables.

Inspect pulse coder cable connections at servo amplifier

Power down the robot (disconnect and lockout). Open the controller cabinet and locate the servo amplifier for the affected axis. Inspect the pulse coder connector (typically labeled CN1 or CN2 depending on amplifier model). Verify the connector is fully seated and the locking tab is engaged. Look for bent pins, corrosion, or contamination.

Always follow LOTO procedures. Verify zero voltage with a multimeter before touching any connections. High voltage remains present for several minutes after power-down.

Inspect motor-side pulse coder connection

Access the motor connection area on the affected axis. Inspect the pulse coder connector at the motor housing. Check for cable strain relief integrity, connector seating, and any visible cable damage near the connector. Flex the cable gently near connectors while watching for intermittent connection.

On older robots with 500,000+ cycles, cable damage often occurs within 6 inches of the motor connector due to repetitive flexing. Look for discoloration or cracks in the cable jacket.

Perform cable continuity and resistance check

Disconnect both ends of the pulse coder cable. Using a multimeter, verify continuity on each conductor and check for shorts between conductors. Measure shield continuity end-to-end (should be <1 ohm). Check insulation resistance between conductors (should be >10 megohms at 500VDC using a megohmmeter).

Document resistance values for future comparison. Degrading insulation will show decreasing megohm readings over time before complete failure.

Replace pulse coder cable if suspect

If any continuity, short, or insulation resistance issue is found, replace with a genuine Fanuc pulse coder cable. Ensure proper routing through cable tracks, maintain minimum bend radius (typically 10x cable diameter), and verify strain relief clamps are properly secured. After installation, jog the axis through full range of motion and monitor for alarm recurrence.

Never use non-Fanuc cables for pulse coder connections. Incorrect impedance or shielding can cause intermittent CRC errors that are difficult to diagnose.

Verify cable shield grounding at controller

With power locked out, open the controller cabinet and locate the main grounding plate (usually copper plate near cable entry). Verify that all pulse coder cable shields are mechanically clamped directly to this grounding plate using the shield clamps. Check for tight mechanical connection, no paint/coating between shield and grounding surface, and no corrosion.

The shield should be grounded at the controller end ONLY, not at both ends. Grounding both ends creates a ground loop that can actually increase noise susceptibility.

Check cable routing separation

Verify that pulse coder cables are routed separately from servo motor power cables. Fanuc specification requires minimum 100mm (4 inches) separation or use of separate cable tracks. If cables cross, they should do so at 90 degrees to minimize coupling. Check that pulse coder cables are not bundled or zip-tied together with power cables.

Never route pulse coder signal cables in the same conduit or cable track as motor power cables, even temporarily during troubleshooting.

Inspect for external EMI sources

Survey the robot work cell for potential EMI sources: resistance welders, large contactors, VFDs, radio transmitters, or arc welding equipment. Note if SRVO-069 correlates with operation of nearby equipment. Check the alarm time stamp (MENU → ALARM → F2 [HIST LOG]) against production logs to identify patterns.

If alarms correlate with weld gun operation, install ferrite cores on the pulse coder cable near both ends (Fanuc part number available). For severe cases, reroute cables or install EMI filters on the interference source.

Verify controller cabinet grounding integrity

Check the main ground connection from the controller cabinet to facility ground. Verify the ground cable is at least 5.5mm² (10 AWG), securely terminated, and has resistance <0.1 ohm to facility ground. Check that the grounding plate inside the cabinet has a solid connection to the cabinet frame.

Use a low-resistance ohmmeter (4-wire Kelvin measurement if available) to verify grounding. Standard multimeters may not reveal marginal ground connections that can cause EMI susceptibility.

Review alarm frequency and pattern

Access the alarm history (MENU → ALARM → F2 [HIST LOG]). If SRVO-069 occurs randomly at various positions and increases in frequency over time, this suggests progressive encoder failure. If it occurs at specific axis positions repeatedly, mechanical misalignment may be stressing the encoder.

Export the alarm log via USB or to a connected PC for analysis. Graph alarm occurrence over time to identify progressive degradation patterns that indicate hardware failure.