Top 10 More FANUC Alarm Codes: Part 2 Troubleshooting Guide

Root causes and fix steps:

• Worn deadman switch contacts — the most common hardware cause. The deadman has two independent channels; degraded contacts cause a timing mismatch. Replace both switches as a matched pair.
• Damaged TP cable — a kinked or pinched cable at the strain relief can intermittently break one channel. Inspect where it exits the pendant housing and at the controller inlet.
• Faulty E-stop button — test by substituting a known-good pendant. If the alarm disappears with the replacement, the original button or cable is the cause.
• Failed safety relay — relay contact switching time may be out of spec. Measure against the safety relay datasheet.
• Reset procedure: press and release the TP E-stop → MENU → ALARM → HIST → F4 [RES_1CH] for SRVO-230, or F5 [RES_2CH] for SRVO-231. If reset fails, navigate to SYSTEM → ESTOP CONFIG.
• CRITICAL: never bypass or ignore this alarm. A degraded channel means partial E-stop coverage only. Fix before returning to production.

Causes and fix sequence:

• Physical obstruction — inspect the robot arm, tool, and fixtures for any interference that was not there before.
• Wrong payload declaration — if payload is set too low, the servo loop does not allocate enough torque and falls behind. Check MENU → SETUP → Frames → PAYLOAD.
• Worn joint bearings or insufficient grease — mechanical friction the servo cannot overcome at the commanded speed. Listen for unusual sounds on the offending joint.
• Incoming power supply drop — low AC voltage starves the servo amplifier. Measure incoming voltage at the cabinet input under load.
• Motor power cable — a loose pin or partial break causes intermittent current loss. Inspect cable and connectors at the motor and amplifier.
• Temporary diagnostic: reduce the speed on the offending motion line. If the alarm disappears at lower speed, the root cause is mechanical or electrical — not a servo gain setting.

Resolution steps:

• Press RESET. The alarm clears only if battery power is now stable — confirm with MENU → SYSTEM → Config → Battery voltage.
• Enable T1 mode and press the deadman switch.
• Jog the affected axis continuously in one direction through at least one complete motor revolution — approximately 20–45 degrees of arm movement depending on gear ratio.
• Verify: MENU → SYSTEM → Master/Cal → Pulse Match. The Pulse Count field must show a real number, not asterisks (****). If asterisks remain, jog further.
• If multiple axes show SRVO-075, jog each in sequence.
• After re-establishing all pulses, verify mastering data is intact: MENU → SYSTEM → Master/Cal → confirm all axes show "DONE." If mastering data was lost, perform Quick Mastering or Zero-Degree Mastering.

Hardware diagnostic tree:

• Step 1 — Isolate: disconnect the motor power cable (U, V, W leads) from the servo amplifier output terminals. Do not power off the controller — only disconnect the motor cable.
• Step 2 — Enable: restore power and try to enable servos (SHIFT + DEADMAN + FWD in T1). If SRVO-045 does not fire, the fault is in the motor or cable. Proceed to insulation test.
• Step 3 — If the alarm fires immediately with the cable disconnected, the fault is in the amplifier. Replace the servo amplifier module.
• Insulation test: with motor cable disconnected, use a megohmmeter at 500V DC to measure insulation from each phase (U, V, W) to PE (ground). Normal: above 1 MΩ. Below 100 kΩ indicates motor winding failure — replace the motor.
• Cable test: if insulation is good, check the motor power cable for intermittent shorts. Also inspect fiber optic signal cable connections at both ends.

Causes and fix:

• Allow to cool fully — do not attempt to reset immediately. The thermostat has hysteresis and must drop well below 95°C before the reset will succeed. Allow at least 20–30 minutes.
• After cooling, perform a cold start (power off → wait 30 seconds → power on) to fully clear the alarm.
• Check motor cooling fans — on larger robots (J1, J2, J3 axes), servo motors have integral cooling fans. A failed fan causes progressive overheating during a production run. Listen for fan operation.
• Check ambient temperature — in Israeli summer conditions, robot enclosures can reach 45–50°C. Verify cabinet fan and filters are clean. Add forced ventilation if needed.
• Reduce cycle speed or add dwell — if the alarm appears only at high cycle rates, the motor is thermally overloaded. Reduce speed or add a pause between cycles.
• Check for mechanical binding — a joint running hotter than others at the same speed indicates mechanical resistance. Check grease condition and bearing health on that axis.

Causes and fix:

• Wrong payload declaration — verify tool weight and center-of-gravity at MENU → SETUP → Frames → PAYLOAD. Even a 1–2 kg error on a borderline payload can cause OVC. Re-run the payload estimation utility if available.
• Insufficient joint lubrication — check grease condition on the affected axis. FANUC recommends grease replacement every 3,500–5,000 hours depending on model. A stiff joint draws significantly more current than a well-lubricated one.
• Excessive tool inertia — if tooling was recently changed and the alarm appeared afterward, the new tool may have higher moment of inertia than declared. Update payload inertia settings.
• Amplifier running hot — OVC threshold effectively drops as amplifier temperature rises. Check cabinet ventilation and clean amplifier air filters.
• Pattern diagnosis: if OVC fires at a specific joint angle every cycle, the cause is likely mechanical at that configuration. Check for binding or insufficient grease at that arm position.

Safe recovery protocol:

• Press RESET on the teach pendant. The robot will enable if no other faults are present.
• Check alarm history (MENU → ALARM → HIST) to see what alarms fired before and during the power event — these reveal the robot's state at the moment of power loss.
• Verify mastering data: MENU → SYSTEM → Master/Cal → confirm all axes show "DONE" status. Power events rarely corrupt mastering, but always confirm before resuming production.
• Inspect the physical robot position — if the arm stopped mid-move, manually jog to a safe home position before resuming AUTO mode.
• Check all I/O states before resuming: conveyors, grippers, fixtures, and safety gates must all be in known states before sending the first AUTO cycle.
• If SRVO-012 fires repeatedly without actual power events, investigate incoming power stability — a failing UPS, voltage sags on the plant supply, or a loose cabinet connection can cause phantom power-fail events.

Root causes and fixes:

• Identify the axis from the alarm message (G:n A:m) — that axis's amplifier module is the starting point. Check which physical joint corresponds to that axis number.
• Too-fast deceleration on that axis — reduce speed, add FINE termination (extends deceleration distance), or reduce CNT values on motions that heavily use that joint.
• Regen resistor for that amplifier module — measure resistance and replace if out of spec. Some multi-axis amplifier units share one regen resistor; a failed resistor affects only the axes on that module.
• Excessive payload inertia at that joint — a high-inertia tool stores more kinetic energy during deceleration. Verify declared payload inertia matches the actual tool.
• If SRVO-043 fires on multiple axes simultaneously, the issue is likely a common power event — check incoming AC voltage and DC bus capacitor condition.

Resolution steps:

• Close the controller cabinet door firmly and press RESET — many SRVO-105 incidents are simply doors left ajar after maintenance.
• If reset fails, check E-stop line wiring using the general connection diagram for your controller (R-30iB or R-30iB Plus) — inspect EAS1/EAS2 and EES1/EES2 terminals.
• Inspect the door interlock switch — a small reed or microswitch on the cabinet door frame. Measure contact continuity with the door closed. Open contact with door closed = faulty switch.
• Check safety relay inputs at the controller backplane — degraded relay contacts can generate transient E-stop signals that trigger SRVO-105.
• After any wiring repair: cycle power and confirm the alarm does not recur before re-enabling the robot.

Causes and fix:

• Measure incoming 3-phase AC voltage at the cabinet input. On 200V systems, normal range is 200–230V (alarm threshold: approximately 253V). On 400V systems, normal range is 380–480V (alarm threshold: approximately 530V).
• If voltage is high, contact the facility electrician — the issue is upstream in plant power distribution, not in the robot.
• Rapid deceleration on high-inertia moves can cause transient HVAL: when the motor regenerates faster than the DC bus can dissipate, voltage climbs. Reduce deceleration rates and check regen resistor condition.
• If incoming voltage is within spec and the alarm is persistent, the amplifier's overvoltage detection circuit may have failed. Replace the servo amplifier.
• Check power factor correction and supply regulation if HVAL correlates with other equipment switching on or off in the facility.