437

Power down the system completely and lock out main breaker. Visually inspect all three-phase input wiring (R, S, T terminals) on the PSM for physical damage, pinched insulation, burn marks, or contamination.

Ensure proper LOTO procedures - residual high voltage remains in DC link capacitors for several minutes after shutdown

Using a megohm meter (500V setting), perform insulation resistance tests between each R/S/T input conductor and ground with wires disconnected from PSM. Minimum acceptable reading is 10 megohms; anything below 1 megohm indicates insulation failure.

Check continuity between R-S, S-T, and T-R phases with wires disconnected. Any reading below infinite resistance indicates a phase-to-phase short requiring immediate cable replacement.

Inspect PSM input terminal block for carbon tracking, loose connections causing arcing, or foreign debris bridging terminals. Clean with electrical contact cleaner and verify torque to specification (typically 1.5-2.0 N·m for αi series PSMs).

Check the PSM LED status. Consistent alarm 437 immediately at power-on before servo-on suggests capacitor issue. Navigate to DIAGNOSIS > SERVO > PSM screen and record DC link voltage reading (should stabilize at 280-320VDC for 200V class, 530-590VDC for 400V class).

Review PSM service life in MAINTENANCE > LIFE menu. If the PSM or capacitor bank shows >50,000 hours or machine age exceeds 8 years, capacitor degradation is likely. Check parameter 8905 (PSM software detection level) - if set too sensitive, adjust to standard value.

With PSM powered down for 10+ minutes and discharged, measure DC link capacitor bank capacitance using capacitance meter. Compare to nameplate value - degradation below 80% of rated capacitance requires capacitor replacement or PSM module replacement.

Discharge DC link through 10kΩ 50W resistor across P-N terminals for minimum 5 minutes before measurement

If capacitors show swelling, electrolyte leakage, or venting, replace entire PSM unit. For αi-PSM series, this requires Fanuc factory replacement. Document serial numbers and system configuration before removal.

Check PSM LED pattern during alarm occurrence. Rapid flashing red or alternating red/green indicates internal hardware fault. Navigate to DIAGNOSIS > SERVO > PSM STATUS and record all fault codes and DC current readings (should be <5A at idle).

Review system alarm history (ALARM > HISTORY) for patterns. If alarm 437 is accompanied by alarms 436 (DC link overvoltage), 438 (regeneration error), or 439 (PSM overload), this indicates PSM control circuit failure rather than external wiring issues.

Disconnect all servo amplifier connections from PSM DC bus (P1/P2 terminals) to isolate PSM. Attempt power-on with no load. If alarm 437 persists with no connected load, PSM internal converter fault is confirmed and unit replacement required.

Ensure all axis drives are disconnected - improper disconnection can cause DC bus transients

Replace PSM unit with identical model (verify αi-PSM model number matches: check suffix for voltage/current rating). After replacement, verify parameter 8900-8909 (PSM configuration) match original settings and perform regeneration discharge test per Fanuc connection manual procedure.