What causes FANUC alarm 607?

One of the three incoming AC power phases to the PSM or PSMR unit is lost or has failed. A blown fuse or tripped breaker on one leg of the three-phase input supply. Loose, corroded, or damaged wiring connection on one of the three input power terminals at the servo amplifier or main disconnect. Faulty magnetic contactor with a welded or failed contact dropping one phase before it reaches the PSM. Utility power supply issue causing a phase loss or severe voltage imbalance on the incoming line.

How do I fix FANUC alarm 607?

1. With power off and locked out, check all three input power terminals on the PSM or PSMR unit for loose or corroded connections and tighten or clean as needed. 2. Use a multimeter to measure AC voltage across all three phase pairs (L1-L2, L2-L3, L1-L3) at the PSM input terminals while power is on. All three readings should be within 10 percent of each other and match your facility voltage spec. 3. Check the main disconnect, fuses, and any circuit breakers feeding the CNC cabinet. Look for a blown fuse or tripped breaker on one leg and replace or reset as required. 4. Inspect the magnetic contactor that feeds the PSM for signs of a burned or failed contact. Measure voltage on the output side of each contact to confirm all three phases are passing through. 5. If all wiring and contactors check out, measure incoming voltage at the facility power panel to rule out a utility-side phase loss before suspecting a failed PSM unit. 6. If input power is confirmed good at all three terminals and the alarm persists, the PSM or PSMR unit itself may have an internal fault and should be replaced or sent for repair.

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FANUC Controller

Servo/Axis · Intermediate · 30-90 minutes depending on root cause

Alarm 607

Fanuc Alarm 607 - n AXIS: CNV. SINGLE PHASE FAILURE

Alarm 607 indicates the Power Supply Module (PSM) or Power Supply Module Regenerative (PSMR) has detected a missing or failed phase on the incoming three-phase AC power supply. This typically occurs when one of the three incoming AC phases (R, S, T or L1, L2, L3) is open, has low voltage, or experiences severe imbalance exceeding the converter's tolerance threshold.

FANUCServo/AxisIntermediate30-90 minutes depending on root cause

607

Fanuc Alarm 607 - n AXIS: CNV. SINGLE PHASE FAILURE

FANUC ALARM 607

Root Cause Summary

Alarm 607 indicates the Power Supply Module (PSM) or Power Supply Module Regenerative (PSMR) has detected a missing or failed phase on the incoming three-phase AC power supply. This typically occurs when one of the three incoming AC phases (R, S, T or L1, L2, L3) is open, has low voltage, or experiences severe imbalance exceeding the converter's tolerance threshold.

Causes and Fixes

1
Power down the system completely. Use a multimeter to measure incoming AC voltage at the primary power disconnect or main breaker feeding the CNC. Verify all three phases (R-S, S-T, T-R) show balanced voltage within 2-3% of nominal (200VAC, 220VAC, 400VAC, 480VAC depending on system).
HIGH VOLTAGE - Use proper PPE and lockout/tagout procedures. Only qualified electricians should perform this measurement.
2
Check all fuses, circuit breakers, and contactors in the main power circuit feeding the CNC cabinet. Inspect fuse holders for corrosion or loose connections. Replace any blown fuses or defective circuit protection devices.
Ensure replacement fuses match the OEM-specified ratings found on the electrical schematic.
3
Inspect terminal blocks TB1 or TB2 (depending on system) at the PSM/PSMR module for loose, burned, or corroded connections on the L1, L2, L3 input terminals. Torque all connections to specification (typically 1.2-1.5 N-m for PSM terminals).
4
Navigate to SYSTEM > DIAGNOSIS > PSM (screen number varies by series: typically #0300 for 0i/30i/31i/32i). Check diagnostic registers DC voltage output and AC input voltage readings. Compare all three phases for balance and proper voltage levels.

DIY Feasiblehigh confidence

Call a technician if:

·PSM module replacement required
·Facility electrical system modifications needed
·Power quality issues beyond machine scope

Prevention

Install power quality monitoring
Perform regular electrical connection inspections
Maintain proper facility power system
Use surge protection devices

Common Mistakes

Not checking all three phases individually
Ignoring voltage imbalance issues
Replacing PSM without verifying input power quality
Not following proper LOTO procedures during electrical checks

Related Alarms

AL-606 AL-608 AL-611

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