SV2

Measure PSU Output Voltage

Using a digital multimeter set to DC voltage mode, measure the output voltage directly at the 24VDC PSU terminals. Ensure the reading is between 20-28VDC as per Fanuc specifications.

Measure under load by ensuring the machine is powered on with typical operations active to detect voltage drops.

Ensure the machine is in a safe state before accessing live terminals to avoid electrical shock.

Inspect PSU Load Conditions

Check if the PSU is overloaded by reviewing the total current draw of connected devices (servo amplifiers, I/O modules, etc.) against the PSU's rated capacity. Temporarily disconnect non-critical loads and re-measure voltage.

Use a clamp meter to measure current draw on the 24VDC line for a quick load assessment.

Do not disconnect critical safety circuits during testing.

Replace or Repair PSU if Necessary

If the voltage remains below 20VDC or fluctuates significantly, replace the PSU with a compatible unit matching the machine's specifications. Alternatively, send the PSU for repair if replacement is not immediately available.

Keep a spare 24VDC PSU on hand for critical machines to minimize downtime.

Ensure proper grounding when installing a new PSU to prevent electrical noise issues.

Visually Inspect Wiring Terminals

Power down the machine and inspect the 24VDC input terminals on the servo amplifier for loose wires, corrosion, or damaged connectors. Look for signs of arcing or discoloration.

Use a flashlight and magnifying glass to spot micro-corrosion on terminal contacts.

Ensure the machine is fully powered off and locked out before inspection to avoid electrical hazards.

Tighten and Clean Connections

Use a screwdriver to tighten any loose terminal screws. If corrosion is present, clean the terminals with electrical contact cleaner and a wire brush, then re-secure the connections.

Apply dielectric grease after cleaning to prevent future corrosion in humid environments.

Do not overtighten screws as this can strip threads or damage terminals.

Test Voltage at Terminals Post-Repair

Power up the machine and measure the voltage directly at the amplifier's input terminals with a multimeter to confirm stable 24VDC (20-28VDC range). If the alarm clears, monitor for recurrence over the next few hours.

Wiggle the wires slightly during measurement to detect intermittent connection issues.

Keep hands clear of live circuits during testing to prevent shock.

Identify Connected Loads on 24VDC Bus

Review the machine's electrical schematic to list all devices powered by the 24VDC bus. Note any recent additions or modifications that might increase load.

Label wires or take photos before disconnecting anything to ensure correct reassembly.

Do not proceed without schematics to avoid disconnecting critical systems.

Measure Total Current Draw

Use a clamp meter to measure the total current draw on the 24VDC bus. Compare this against the PSU's rated capacity to determine if overloading is occurring.

Measure at different machine operation states (idle, full load) to capture peak draw.

Ensure proper meter settings to avoid damage or inaccurate readings.

Reduce Load and Retest

Temporarily disconnect non-critical devices from the 24VDC bus, then re-measure voltage at the servo amplifier input. If voltage returns to normal and the alarm clears, redistribute or upgrade the PSU capacity.

Consider adding a secondary PSU for non-critical loads to isolate servo power needs.

Do not leave critical safety devices disconnected during operation.

Confirm Input Voltage at Amplifier

Measure the 24VDC input directly at the servo amplifier terminals with a multimeter to ensure it is within the 20-28VDC range. Document the exact reading.

Use a high-quality multimeter for accurate readings, as cheap meters can give false results.

Ensure the machine is in a safe state before accessing live terminals.

Check for Other Amplifier Alarms

Inspect the amplifier's 7-segment display or diagnostic LEDs for additional error codes that might indicate internal failure beyond low voltage. Record any findings for reference.

Cross-reference additional alarms with the Fanuc manual to narrow down internal issues.

Do not attempt internal repairs without proper training or documentation.

Arrange for Amplifier Repair or Replacement

If input voltage is correct but the LV alarm persists, the internal control circuit is likely faulty. Contact a certified Fanuc repair center for service or order a replacement amplifier matching the model number.

Keep a spare amplifier for critical axes to minimize downtime during repairs.

Ensure proper ESD precautions when handling servo amplifiers to avoid further damage.

Monitor Voltage Stability Over Time

Connect a multimeter or data logger to the 24VDC output of the PSU and monitor for fluctuations or drops below 20VDC over a period of 10-15 minutes during normal operation.

Use a multimeter with a min/max function to capture brief voltage dips.

Avoid touching live circuits during monitoring to prevent injury.

Inspect PSU for Capacitor Wear

Power down the machine and visually inspect the PSU for bulging or leaking capacitors. These are signs of failure that can cause voltage instability.

Capacitors near heat sources or vents are more likely to fail—check those first.

Ensure the PSU is fully discharged before inspection to avoid residual voltage shock.

Replace Faulty Capacitors or PSU

If capacitors show signs of failure or voltage remains unstable, replace the affected components or the entire PSU. Use only Fanuc-approved or equivalent parts for compatibility.

Consider proactive replacement of capacitors in older machines as preventive maintenance.

Improper capacitor replacement can cause further damage—consult a technician if unsure.