SRVO-045

Identify the Faulted Axis

On the teach pendant, press MENU → ALARM → F1 [DETAIL]. Note the axis number specified in the alarm (e.g., 'Group: 1 Axis: 3' indicates J3). Record the alarm occurrence count and whether it happens at specific positions or during motion. Check MENU → SYSTEM → Variables → $SCR_GRP[1].$CURR_ANG to note current joint positions.

If the alarm occurs at a specific joint angle repeatedly, suspect cable damage at that flexing position. Check the cable track and external cable routing near that axis.

Power Down and Lockout Controller

Execute a controlled shutdown: MENU → SYSTEM → Master/Cal → Controlled Start (set to FALSE if needed). Turn the controller main breaker OFF and engage lockout/tagout procedures. Wait 5 minutes for capacitor discharge in the servo amplifier before opening the cabinet. Verify zero voltage with a multimeter on the amplifier DC bus.

Servo amplifiers retain lethal voltage for several minutes after power-off. Never open the cabinet or disconnect cables until proper discharge time has elapsed and voltage is verified at zero.

Disconnect and Inspect Motor Cable at Amplifier

Locate the servo amplifier for the faulted axis in the controller cabinet (consult the axis-to-amplifier map on the cabinet door or Maintenance Manual Appendix B). Disconnect the U-V-W motor power connector from the amplifier CN2 connector. Inspect connector pins for carbon tracking, discoloration, or debris. Examine the cable jacket along the entire run for cuts, pinch points, oil contamination, or thermal damage.

Use a flashlight and magnifying glass to inspect connector pins carefully. Even small carbon tracks between pins can cause intermittent shorts. Clean connectors with electrical contact cleaner and allow to dry completely.

Perform Cable Insulation Resistance Test

Using a 500V megohmmeter (insulation tester), measure insulation resistance between U-V, V-W, W-U, and each phase to ground/shield. All measurements should exceed 10 MΩ (preferably >100 MΩ). Any reading below 1 MΩ indicates insulation failure. Test at the amplifier side first, then at the motor side if accessible. Flex the cable through its full range of motion while testing to detect intermittent faults.

For intermittent faults that only appear during motion, secure the megohmmeter leads and manually move the robot joint through its full range while monitoring the reading. A sudden drop indicates position-dependent cable damage.

Test Amplifier Without Motor Connected

With the motor cable disconnected from the amplifier, restore power to the controller. From the teach pendant, attempt to enable servo power (Hold SHIFT + press and hold DEADMAN switch + press FWD or BWD). If SRVO-045 does not occur, the fault is confirmed in the motor or cable. If the alarm still occurs immediately, proceed to amplifier replacement diagnostics.

Do not leave the motor cable disconnected and attempt jogging. This test only verifies if the amplifier can power up without tripping. Never operate the robot with cables disconnected.

Access and Disconnect Motor at J-Box

After confirming cable integrity, access the motor connection at the robot joint junction box (J-box). For wrist axes, this typically requires removing the J3 arm cover. Disconnect the motor power leads (U-V-W) from the cable at the motor-side connector. Label connections before disconnection. Inspect the motor connector and cable termination for oil contamination, corrosion, or loose crimps.

Wrist motors (J4/J5/J6) are especially prone to coolant ingress in machining applications. Look for discoloration or crystalline residue around the motor connector housing indicating liquid contamination.

Measure Motor Winding Resistance

Using a precision digital multimeter, measure DC resistance between motor terminals: U-V, V-W, and W-U. For typical Fanuc servo motors, expect 0.5-5Ω depending on motor size. All three measurements should be within 5% of each other. A significantly lower reading (near zero ohms) indicates a shorted winding. An open circuit (infinite resistance) indicates a broken winding.

Temperature affects resistance readings. If possible, allow the motor to reach ambient temperature before testing. Record the ambient temperature with your measurements for accurate comparison to factory specifications in the Mechanical Unit Maintenance Manual.

Test Motor-to-Ground Insulation

Using a 500V megohmmeter, measure insulation resistance from each motor terminal (U, V, W) to the motor frame/mounting flange. Readings should exceed 10 MΩ. Any reading below 1 MΩ indicates winding-to-frame insulation failure. Also check motor brake winding to frame if the axis is equipped with a holding brake.

Ensure the motor brake cable is disconnected before insulation testing to avoid damaging the brake rectifier circuit with high test voltage.

Perform Motor Rotation and Bearing Check

Manually rotate the motor shaft (if accessible) or move the joint through its range. Feel for roughness, grinding, or tight spots indicating bearing failure. A failing bearing can allow rotor-to-stator contact causing intermittent shorts. Listen for noise. Check for excessive shaft end-play by attempting to move the shaft axially.

On smaller wrist motors, bearing failure often causes position feedback errors before causing HCAL alarms. Check alarm history (MENU → ALARM → F5 [HIST]) for preceding SRVO-065 (excess position error) or SRVO-075 (overheat) alarms on the same axis.