SRVO-073

Verify cable routing and separation

Inspect robot interconnection cables from robot base to controller. Ensure pulse coder signal cables maintain minimum 300mm separation from AC power cables, servo motor power lines, and welding equipment. Check that cables are not bundled together with power wiring in the same conduit or cable tray.

On older installations, check if anyone has added equipment nearby that could generate EMI - VFDs, welding controllers, or induction heaters are common culprits.

Inspect cable shield grounding at both ends

At the robot base connection (axis motor connectors), verify the cable shield is properly terminated to the connector backshell and making solid contact with the robot mounting surface. At the controller end, verify shields terminate at the cabinet ground plate via the connector backshells on the servo amplifier panel. Use a DMM to verify continuity between shield and ground (should be <1 ohm).

Disconnect all power and wait 5 minutes for capacitor discharge before opening controller cabinet or manipulating cables.

Check for ground loops and grounding configuration

Verify the robot base is solidly grounded to facility ground. Check that controller cabinet ground is connected to the same ground point (single-point grounding). Measure AC voltage between robot base and controller ground with robot powered on - should be less than 1VAC. Higher voltage indicates ground loop or poor facility grounding.

If the alarm occurs during specific motions or when certain nearby equipment operates, this strongly points to EMI rather than hardware failure.

Install or check ferrite cores on pulse coder cables

If noise issues persist, install snap-on ferrite cores (FANUC part A660-2005-T505 or equivalent) on the pulse coder cables near both ends. Place cores within 100mm of connectors on both robot base side and amplifier side. Ensure at least 2-3 wraps through the core for maximum attenuation.

On R-30iB controllers with high-speed serial pulse coders, ferrite cores are sometimes pre-installed from factory. Check for their presence before adding more.

Perform visual and tactile cable inspection

With robot powered off, manually move each axis through full range of motion while inspecting the interconnection cable from J1 base to J3 upper arm, and J4-J6 wrist cables. Look for: cracked outer jacket, exposed conductors, flat spots from pinching, excessive bend radius violations (<10x cable diameter), or oil/coolant contamination that degrades insulation.

Enable the deadman switch and have pendant ready for emergency stop when manually moving axes. Large robots require multiple people.

Check cable continuity and insulation resistance

Disconnect cable connectors at robot base and controller end. Using DMM, verify continuity on all pulse coder signal pairs (typically labeled ENC or SER). Resistance should be <5 ohms end-to-end. Then perform insulation resistance test using megohmmeter at 250VDC between conductors and shield - should be >10 megohms. Values below this indicate insulation breakdown.

Tag and photograph all connector positions before disconnecting. Incorrect reconnection can damage servo amplifiers.

Test for intermittent connection during motion

Reconnect cables and access MENU > SYSTEM > Master/Cal > Pulse Display. Monitor pulse counts while slowly jogging the axis with the alarm. Watch for erratic pulse count jumps, freezing, or resetting to zero which indicates intermittent connection. Note which axis positions trigger the behavior to identify cable flex zones with damage.

If alarm only occurs at specific positions (e.g., J1 at +170 degrees), the cable has likely failed at that flex point. This narrows down where to focus cable replacement or repair.

Inspect cable dress and strain relief

Check that cable support brackets, cable tracks, and strain relief clamps are intact and properly supporting the cable. Verify the cable dress matches FANUC's recommended routing in the maintenance manual. Look for modifications or missing clips that allow excessive cable movement or rubbing against robot structure.

Take photos of cable routing before any repairs. Incorrect re-dressing after cable replacement is a leading cause of premature cable failure.

Perform diagnostic pulse coder reset procedure

From teach pendant: MENU > SYSTEM > Variables, set $MCR.$SPC_RESET = TRUE. This clears the pulse coder communication error flags and re-initializes the serial communication. Power off the controller completely (not E-stop, actual power off), wait 30 seconds, then power back on. Navigate to MENU > ALARM > alarm log. If CMAL returns immediately on power-up without motion, this indicates likely hardware failure.

The $SPC_RESET variable only exists on R-30iA and newer controllers with serial pulse coders. Older absolute encoders use different reset procedures.

Check pulse coder diagnostic parameters

Access MENU > MAINTENANCE > Servo > Servo Setup. For the affected axis, check: Communication Error Count (should be 0 or very low), Signal Strength (should be nominal values per maintenance manual), and Battery Voltage for absolute encoders (>3.0V). High error counts or low signal strength indicate failing pulse coder hardware requiring replacement.

Do not clear error counters until you have documented the values - they provide important diagnostic information about failure frequency.