SRVO-047

Check alarm history for pattern

On the teach pendant, navigate to MENU > ALARM > F5 (LOG) to review alarm history. Look for whether SRVO-047 occurs on single or multiple axes, intermittently or constantly. Multiple axes indicate PSU issue; single axis suggests amplifier or cable problem.

If the alarm occurs during high-load motions or after warmup, this strongly indicates PSU capacitor degradation rather than complete failure.

Measure PSU output voltage

Power down the controller and LOTO. Remove the controller front cover. Using a multimeter, measure DC voltage at the PSU output terminal block (typically labeled +24V and 0V). With controller powered on but motors off, voltage should read 24VDC ±1V. Under 23VDC indicates PSU degradation.

High voltage present. Ensure proper lockout/tagout procedures. Do not touch live terminals. Use insulated test probes only.

Measure voltage at servo amplifier input

Locate the servo amplifier connector CNVS (control voltage supply) on the axis showing the alarm. Measure voltage between pins designated +24V and 0V while controller is powered. Compare to PSU output voltage. A drop of more than 0.5V indicates cable or connector resistance issues.

On R-30iB systems, the CNVS connector is typically a white 6-pin connector on the amplifier front. Refer to the amplifier label for exact pin designations.

Load test the power supply

With motors enabled and robot stationary, command a low-speed motion on multiple axes simultaneously. Monitor PSU voltage during motion. If voltage drops below 23VDC under load, PSU requires replacement. Normal operation should maintain 23.5-24.5VDC even under full load.

Ensure robot workspace is clear and E-stop is accessible. Have another person monitor robot motion during this test.

Check PSU LED indicators

Examine the power supply unit LED indicators. Green LED should be solid. Red or amber LEDs, or no LED, indicate PSU fault. On R-30iB Plus controllers, the PSU LED is visible through the front panel. Refer to Maintenance Manual section 3.3 for LED status meanings specific to your PSU model (A06B-6096, A06B-6117, etc.).

If PSU LED is green but voltage is low, the PSU feedback circuit may be functioning while output stage is failing—a common failure mode requiring PSU replacement.

Inspect control cable connections

Power down and LOTO. Visually inspect all connectors on the control power distribution rail and at each servo amplifier CNVS connector. Look for discoloration, corrosion, or heat damage. Check that connector locking tabs are fully engaged. On R-30iB, these are typically white multi-pin connectors.

Do not disconnect connectors while powered. This can damage servo amplifiers or create arc flash hazards.

Measure voltage drop across cables

With controller powered on, measure voltage at PSU output terminals, then at the servo amplifier CNVS connector for the affected axis. Voltage drop should be less than 0.3V. If drop exceeds 0.5V, inspect cable routing for pinch points, check connector pins for corrosion, and verify wire crimps are secure.

Use a separate ground reference point rather than daisy-chaining meter leads to avoid false readings from ground potential differences.

Check terminal block tightness

Using appropriate torque screwdriver, verify all control power terminal blocks are torqued to specification (typically 0.5-0.6 N⋅m for signal terminals). Loose terminals create resistance and heat, causing voltage drop. Pay special attention to the power distribution terminal blocks inside the controller cabinet.

After retorquing, operate the robot and use a thermal camera or infrared thermometer to check for hot spots on connections—temperatures more than 10°C above ambient indicate resistance problems.

Verify control cable gauge and length

Confirm control power cables are the correct gauge per Fanuc specifications (typically 0.75mm² or larger for control voltage). If cables have been extended or modified, inadequate wire gauge can cause excessive voltage drop. Measure actual cable length and compare to Fanuc standard cable lengths for your robot model.

Custom or extended robot installations sometimes use undersized control cables. If cable runs exceed 10 meters, voltage drop calculations may require larger gauge wire than standard.

Identify affected axis amplifier

Review the alarm detail to identify which axis (J1-J6) triggered SRVO-047. On teach pendant: MENU > ALARM > select SRVO-047 > F3 (DETAIL). Note the axis number. Multiple simultaneous axes suggest PSU problem; single axis indicates amplifier issue.

If the same axis repeatedly triggers this alarm while others are normal and PSU voltage is good, the amplifier is likely faulty.