SP51

Check PSM LED Display for Alarms

Inspect the LED display on the PSM for any alarm codes or error indicators. Note down any codes displayed as they will provide specific insight into the PSM issue.

Refer to the FANUC PSM alarm code manual for detailed descriptions of any displayed codes.

Ensure the machine is powered down before accessing the PSM to avoid electrical shock.

Reset PSM if Alarm is Present

If an alarm is displayed, attempt a reset by powering down the machine, waiting 5 minutes, and powering it back up. Observe if the alarm reappears on the PSM display.

A recurring alarm after reset often indicates a hardware fault in the PSM requiring replacement or repair.

Do not repeatedly reset without addressing the root cause as it may worsen the issue.

Test PSM Output Voltage

Using a multimeter set to DC voltage, measure the output voltage at the PSM terminals. Compare the reading to the expected range (280-325VDC for 200V class, 560-650VDC for 400V class).

If the voltage is significantly below spec even with no load, the PSM likely needs professional servicing.

High voltage is present; ensure proper insulation and safety gear while measuring.

Measure AC Input Voltage at PSM

Using a multimeter set to AC voltage, measure the voltage between each pair of phases at the PSM input terminals. Ensure all three phases are present and within the machine's specified range (typically 200-240VAC or 380-480VAC).

A difference of more than 5% between phases often indicates an imbalance or missing phase.

High voltage present; use insulated tools and wear appropriate PPE.

Inspect Upstream Power Supply

If a phase is missing or voltage is low, check the upstream power source, including circuit breakers, fuses, and transformers feeding the machine, for faults or tripped conditions.

Look for signs of overheating or burnt components in the power supply chain as indicators of issues.

Do not bypass tripped breakers; address the root cause first.

Contact Facility Electrician if Needed

If the issue lies beyond the machine (e.g., facility power supply), coordinate with a qualified electrician to restore proper AC input to the machine. Retest voltage after corrections are made.

Document voltage readings before and after corrections for future reference.

Do not attempt facility-level electrical repairs unless qualified.

Monitor DC Bus Voltage During Startup

Using a multimeter or oscilloscope, monitor the DC bus voltage at the PSM output during machine startup. Observe if the voltage ramps up slowly or fails to reach the expected level (280-325VDC or 560-650VDC).

A slow ramp-up or plateau below spec often points to a pre-charge circuit issue.

High voltage hazard; ensure proper safety protocols are followed.

Check PSM for Pre-Charge Related Alarms

Inspect the PSM LED display for specific alarms related to pre-charge circuit failure (refer to FANUC documentation for relevant codes). Note any recurring or specific error messages.

Some PSM models log pre-charge faults in diagnostic memory; access this if available.

Do not ignore minor alarms; they may escalate if unaddressed.

Inspect Pre-Charge Resistors and Relays

If accessible, visually inspect the pre-charge resistors and relays inside the PSM for signs of damage, burning, or wear. Replace components if damage is evident, or escalate to a technician for repair.

Burnt smells or discoloration are clear indicators of pre-charge component failure.

Only attempt internal PSM inspection if trained; risk of shock or further damage.

Inspect DC Bus Wiring Connections

Visually check the DC bus wiring connections at both the PSM output and spindle drive input terminals for looseness, corrosion, or damage. Tighten any loose connections using the specified torque values.

Use a torque wrench to ensure connections are tightened to manufacturer specs.

Power down the machine completely before inspecting or tightening connections.

Measure Voltage Drop Across Wiring

With the machine powered on, measure the DC voltage at the PSM output and again at the spindle drive input. A difference of more than 1-2V indicates high resistance in the wiring.

Even small voltage drops can cause issues under high load; don’t overlook minor discrepancies.

High voltage present; use insulated probes and extreme caution.

Replace Damaged Wiring if Necessary

If wiring shows signs of damage (fraying, burns, or corrosion), replace it with wiring of the same gauge and insulation rating as specified by FANUC. Retest voltage after replacement.

Label wires before removal to ensure correct reconnection.

Improper wiring replacement can cause shorts or further damage; double-check connections.

Test DC Bus Voltage Stability Under Load

Operate the spindle at varying loads while monitoring DC bus voltage with a multimeter or oscilloscope. Significant voltage dips (more than 10-15V) during load changes suggest capacitor degradation.

Use a data-logging multimeter to capture transient voltage drops more accurately.

High voltage hazard; ensure proper safety measures during testing.

Visually Inspect Capacitor Bank

If accessible, power down the spindle drive and inspect the capacitor bank for physical signs of failure such as bulging tops, leaking electrolyte, or burnt smells. Note any abnormalities.

Capacitors often fail in groups; if one is damaged, consider replacing the entire bank.

Capacitors may retain charge even when powered off; discharge them safely before inspection.

Escalate for Capacitor Replacement

If capacitors are degraded, do not attempt DIY replacement unless trained. Contact a certified FANUC technician to service the spindle drive and replace the capacitor bank.

Ask the technician for a full diagnostic of the drive during service to catch other potential issues.

Incorrect capacitor replacement can lead to catastrophic failure; professional service is recommended.