FANUC Servo Amplifier Alarm Codes

PSM alarm 1: Main circuit IPM abnormal / input overcurrent

What it means: On PSM-5.5i to PSM-15i the main circuit power module (IPM) has detected an abnormal condition; on PSM-15i to PSM-37i overcurrent flowed into the input of the main circuit.^[1][3]

On the CNC screen: SV0437 (Series 15i) / 437 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: input circuit overcurrent

Likely causes

• Input supply voltage imbalance
• AC reactor specification does not match the PSM in use
• Low control supply voltage to the IPM (smaller PSM models)
• Failed IPM or IGBT in the PSM

First checks, in this order

1. Measure the three input phases and confirm they are balanced and within the PSM input specification
2. Check that the AC reactor fitted is the one specified for this PSM model
3. If supply and reactor are correct, the manual's next step is replacing the IPM, IGBT or power unit, so send the PSM for repair or exchange

PSM alarm 2: Control circuit cooling fan stopped

What it means: A cooling fan for the PSM control circuit has stopped (PSM and PSMR).^[1][3]

On the CNC screen: SV0443 (Series 15i) / 443 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: cooling fan stopped

Likely causes

• Control circuit cooling fan broken or not turning
• Fan blocked by foreign material

First checks, in this order

1. With control power on, check whether the control circuit fan turns normally
2. Look for foreign material in the fan
3. Replace the fan if it does not turn

PSM alarm 3: Main circuit heat sink overheat

What it means: The temperature of the main circuit heat sink has risen abnormally.^[1][3]

On the CNC screen: SV0431 (Series 15i) / 431 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: main circuit overload

Likely causes

• Main circuit cooling fan broken
• Dust built up on the heat sink and fan
• Overload from the machine's operating conditions
• Control PCB not fully seated, since a loose connector between the control and power boards can raise this alarm

First checks, in this order

1. Check that the main circuit cooling fan turns normally
2. Clean the cooling system with a vacuum cleaner (the manual warns that compressed air spreads conductive dust)
3. Review the duty cycle for overload
4. Push the faceplate (control PCB) in as far as it will go

PSM alarm 4: DC link undervoltage

What it means: In the main circuit, the DC link voltage has dropped (PSM and PSMR).^[1][3]

On the CNC screen: SV0433 (Series 15i) / 433 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: DC link undervoltage

Likely causes

• A short power dip on the supply
• Low input supply voltage
• Main power switched off while the emergency stop was released (sequence fault)

First checks, in this order

1. Check the plant supply for dips at the time of the alarm
2. Measure the input voltage against the PSM specification
3. Check the machine sequence so main power is never dropped while the emergency stop is released

PSM alarm 5: DC link precharge failure

What it means: The main circuit capacitor was not recharged within the specified time (PSM and PSMR).^[1][3]

On the CNC screen: SV0442 (Series 15i) / 442 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: DC link precharge failure

Likely causes

• Too many SVM and/or SPM units connected for this PSM
• Short circuit on the DC link
• Defective recharge current limiting resistor

First checks, in this order

1. Confirm the connected SVM and SPM units are within the PSM specification
2. With power off and the charge LED out, inspect the DC link bars and connections for a short
3. If both are fine, the manual's fix for a bad recharge resistor is replacing the distributing board

PSM alarm 6: Control power supply undervoltage

What it means: The PSM control power supply voltage has dropped (PSM and PSMR).^[1]

On the CNC screen: SV0432 (Series 15i) / 432 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: control power supply undervoltage

Likely causes

• Low control power input voltage
• Dips on the supply feeding the control power

First checks, in this order

1. Measure the control power input to the PSM (the start-up procedure feeds it 200 VAC)
2. Check the incoming supply for dips

PSM alarm 7: DC link overvoltage

What it means: In the main circuit, the DC link voltage is abnormally high (PSM and PSMR).^[1][3]

On the CNC screen: SV0439 (Series 15i) / 439 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: DC link overvoltage

Likely causes

• Excessive regenerated power, so the PSM capacity is too small
• Output impedance of the AC power source too high
• Main power switched off while the emergency stop was released (sequence fault)

First checks, in this order

1. Check that the PSM model is sized for the connected motors
2. Check source impedance: the manual calls it normal if the voltage variation at maximum output is within 7 percent
3. Check the power-off sequence against the emergency stop

PSM alarm 8: Excessive regenerative power (PSMR only)

What it means: On the resistance regeneration type PSMR, there is excessive short-term regenerative power.^[1]

On the CNC screen: SV0605 (Series 15i) / 605 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: excessive regenerative power

Likely causes

• Regenerative resistance insufficient
• Regenerative circuit failure

First checks, in this order

1. Check the regenerative resistor specification against the PSMR
2. If the resistor is correct, the regenerative circuit is abnormal and the manual says replace the PSMR

PSM alarm A: External cooling fin fan stopped

What it means: A cooling fan on the PSM external cooling fin (radiator) has stopped.^[1]

On the CNC screen: SV0606 (Series 15i) / 606 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: cooling fan stopped of the radiator

Likely causes

• External cooling fin fan broken
• Control PCB not fully seated, so a connector between the control and power boards is loose

First checks, in this order

1. Check whether the external cooling fin fan turns normally
2. Replace the fan if it does not turn
3. Push the control PCB fully home

PSM alarm E: Input power open phase

What it means: The input power supply is abnormal because a phase is open (PSM and PSMR).^[1]

On the CNC screen: SV0607 (Series 15i) / 607 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Open phase in the converter main power supply

Likely causes

• A missing phase on the incoming supply
• A loose or broken connection in the input wiring

First checks, in this order

1. Measure all three phase voltages at the PSM input
2. If the supply voltages are fine, check the input connections

PSM alarm H: Regenerative resistor overheat (PSMR only)

What it means: On the PSMR, the temperature of the regenerative resistor has risen abnormally.^[1]

On the CNC screen: SV0440 (Series 15i) / 440 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: excessive deceleration power

Likely causes

• Regenerative resistor not detected (wiring)
• Regenerative resistance insufficient
• Excessive regenerative power from frequent acceleration and deceleration
• Regenerative resistor cooling fan stopped

First checks, in this order

1. Check the wiring to the regenerative resistor
2. Check the resistor specification
3. Reduce how often the axes accelerate and decelerate
4. Check whether the regenerative resistor cooling fan has stopped

SVM alarm 1: Inverter: internal cooling fan stopped

What it means: The internal cooling fan of the SVM has stopped.^[1][2]

On the CNC screen: SV0444 (Series 15i) / 444 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: internal cooling fan stopped

Likely causes

• Fan not running
• Fan motor connector or cable defective
• SVM failure

First checks, in this order

1. Check the fan for foreign material
2. Push the faceplate (control PCB) in as far as it will go
3. Check that the fan connector is attached correctly
4. Replace the fan, then the SVM if the alarm stays

SVM alarm 2: Inverter: control power supply undervoltage

What it means: The 24 V control power the SVM receives from the PSM is too low.^[1][2]

On the CNC screen: SV0434 (Series 15i) / 434 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: control power supply undervoltage

Likely causes

• Low 24 V output from the PSM
• CXA2A/B connector or cable defective
• SVM failure

First checks, in this order

1. Check the amplifier three-phase input is not lower than 85 percent of rated input voltage
2. Measure the 24 V supply from the PSM (normally not lower than 22.8 V)
3. Check the CXA2A/B connector and cable
4. Replace the SVM

SVM alarm 5: Inverter: DC link undervoltage

What it means: The SVM sees low voltage on the DC link.^[1][2]

On the CNC screen: SV0435 (Series 15i) / 435 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: DC link undervoltage

Likely causes

• Low input voltage
• DC link short bar poorly connected
• SVM failure

First checks, in this order

1. Check the screws on the DC link connection bar are tight
2. If more than one module shows this alarm, troubleshoot the PSM as for PSM code 4
3. If only one SVM shows it, push that SVM's faceplate fully home
4. Replace the SVM that shows the alarm

SVM alarm 6: Inverter: overheat

What it means: The SVM has overheated.^[1][2]

On the CNC screen: SV0602 (Series 15i) / 602 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: overheat

Likely causes

• Motor used under a harsh condition, above its continuous rating
• High ambient temperature or poor cabinet cooling
• SVM failure

First checks, in this order

1. Check the motor is used at or below its continuous rating
2. Inspect the cabinet fans and filters
3. Check the ambient temperature is not too high
4. Push the faceplate fully home, then replace the SVM

SVM alarm F: Inverter: cooling fan stopped of the radiator

What it means: The heat sink (radiator) cooling fan of the SVM has stopped.^[1][2]

On the CNC screen: SV0601 (Series 15i) / 601 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: cooling fan stopped of the radiator

Likely causes

• Fan not running
• Fan motor connector or cable defective
• SVM failure

First checks, in this order

1. Check the fan for foreign material
2. Push the faceplate fully home
3. Check that the fan connector is attached correctly
4. Replace the fan, then the SVM if the alarm stays

SVM alarm P: Communication error between amplifier and module

What it means: The SVM reports a communication error between the amplifier and the other modules; the manual points at the CXA2A/B link.^[1][2]

On the CNC screen: SV0604 (Series 15i) / 604 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Communication error between amplifier and module

Likely causes

• CXA2A/B connector or cable defective
• SVM failure

First checks, in this order

1. Check the CXA2A/B connector and cable
2. Replace the control PCB
3. Replace the SVM

SVM alarm 8: Inverter: DC link current alarm

What it means: The SVM detected abnormal current in its DC link (code 8 without a dot).^[1][2]

On the CNC screen: SV0600 (Series 15i) / 600 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: DC link current alarm

Likely causes

• Short circuit or ground fault between motor power lead phases
• Short circuit or ground fault in the motor windings
• SVM failure

First checks, in this order

1. Disconnect the motor power leads from the SVM and release the emergency stop; if the alarm still occurs, replace the SVM
2. With the leads off, check insulation between PE and the U, V and W leads; if insulation is normal, replace the SVM
3. If insulation is low, separate the motor from its leads and test each, then replace the motor or the power lead that is bad

SVM alarm 8., 9., A. (with dot): Inverter: IPM alarm (L, M, N axis)

What it means: The power module (IPM) of the L axis (8.), M axis (9.) or N axis (A.) has detected an abnormal condition.^[1][2]

On the CNC screen: SV0449 (Series 15i) / 449 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: IPM alarm

Likely causes

• Short circuit or ground fault between power lead phases
• Short circuit or ground fault in the motor windings
• SVM failure

First checks, in this order

1. Push the faceplate (control PCB) fully home
2. Disconnect the motor power leads and release the emergency stop; if the IPM alarm still occurs, replace the SVM
3. Insulation test (megger) PE to U, V, W with the leads off the SVM
4. If insulation is low, test the motor and the cable separately and replace the bad one

SVM alarm 8., 9., A. (with dot): Inverter: IPM alarm (OH), overheat (L, M, N axis)

What it means: The IPM of the L axis (8.), M axis (9.) or N axis (A.) has overheated; the display is the same as the plain IPM alarm, so use the CNC alarm number to tell them apart.^[1][2]

On the CNC screen: SV0603 (Series 15i) / 603 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: IPM alarm (OH)

Likely causes

• Motor used under a harsh condition
• High ambient temperature
• SVM failure

First checks, in this order

1. Push the faceplate fully home
2. Check that the heat sink cooling fan is running
3. Check the motor is used at or below its continuous rating
4. Check cabinet cooling (fans, filters) and ambient temperature, then replace the SVM

SVM alarm b, c, d: Inverter: motor current alarm (L, M, N axis)

What it means: Abnormal motor current on the L axis (b), M axis (c) or N axis (d).^[1][2]

On the CNC screen: SV0438 (Series 15i) / 438 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Inverter: motor current alarm

Likely causes

• Short circuit or ground fault in the power leads or motor windings
• Incorrect motor ID setting or non-standard current parameters
• Motor used too hard on rapid acceleration and deceleration
• SVM or motor failure

First checks, in this order

1. Check servo parameters 2004, 2040, 2041 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i) or 1809, 1852, 1853 (Series 15i) hold the standard values for the motor
2. If it only trips on rapid acceleration or deceleration, increase the time constant and retest
3. Push the faceplate home, disconnect the motor leads and release the emergency stop; if the alarm repeats, replace the SVM
4. Otherwise insulation test the motor and leads and replace the bad part

SVM alarm - (blinking): Inverter: abnormal control power supply

What it means: A blinking dash means the SVM control power is abnormal, which the status table describes as a shorted cable, usually the pulsecoder feedback cable (JF*).^[1]

Likely causes

• Feedback cable (JF*) or connector shorted
• Motor (pulsecoder) failure
• SVM failure

First checks, in this order

1. Unplug the feedback cable (JF*) at the SVM and switch on; if it still blinks, replace the SVM
2. If it stops, plug the cable back in at the SVM, unplug it at the pulsecoder and switch on
3. Still blinking means replace the cable; blinking stops means replace the motor

SVM alarm U: Inverter: FSSB communication error (COP10B)

What it means: The FSSB optical link on the CNC side (COP10B) has failed; a brief U blink at CNC power-on followed by a steady '-' is normal.^[1]

Likely causes

• COP10B optical cable or connector failure
• SVM failure
• CNC servo card failure

First checks, in this order

1. Among the units showing U, find the one nearest the CNC and replace the optical cable into its COP10B
2. Replace that SVM
3. Replace the next SVM toward the CNC (the COP10B side)
4. Replace the servo card in the CNC

SVM alarm L: Inverter: FSSB communication error (COP10A)

What it means: The FSSB optical link on the outgoing side (COP10A) has failed.^[1]

Likely causes

• COP10A optical cable or connector failure
• SVM failure

First checks, in this order

1. Among the units showing L, find the one farthest from the CNC and replace the optical cable from its COP10A
2. Replace that SVM
3. Replace the next SVM downstream on the COP10A side

Converter: main circuit IPM abnormal (βi SVPM: STATUS2 '-' with STATUS1 '30')

What it means: The main circuit power module (IPM) of the βi SVPM converter has detected an abnormal condition.^[4]

On the CNC screen: 437 (servo) / 9030 (spindle) on Series 16i, 18i, 20i, 21i, 0i, Power Mate i: Converter: input circuit overcurrent

Likely causes

• Low control supply voltage to the IPM
• Input supply voltage imbalance
• AC reactor does not match the SVPM
• IPM failure

First checks, in this order

1. Measure the three input phases for balance
2. Check the AC reactor specification against the SVPM
3. If both are fine, the manual calls for replacing the power unit or IPM

Converter: main circuit heat sink overheat (βi SVPM: STATUS2 '-' with STATUS1 '58')

What it means: The temperature of the SVPM main circuit heat sink has risen abnormally.^[4]

On the CNC screen: 431 (servo) / 9058 (spindle): Converter: main circuit overload

Likely causes

• Cooling fan broken
• Dust accumulation
• Overload

First checks, in this order

1. Check the cooling fan turns normally and replace it if not
2. Clean the cooling system with a vacuum cleaner
3. Review the operating conditions for overload

Converter: DC link undervoltage (βi SVPM: STATUS2 '-' with STATUS1 '51')

What it means: In the SVPM main circuit, the DC link voltage has dropped.^[4]

On the CNC screen: 433 (servo) / 9051 (spindle): Converter: DC link undervoltage

Likely causes

• Short power dip
• Low input supply voltage
• Main power switched off while the emergency stop was released

First checks, in this order

1. Check the supply for dips
2. Measure input voltage against the SVPM specification
3. Check the power-off sequence against the emergency stop

Converter: DC link precharge failure (βi SVPM: STATUS2 '-' with STATUS1 '33')

What it means: The SVPM main circuit capacitor was not recharged within the specified time.^[4]

On the CNC screen: 442 (servo) / 9033 (spindle): Converter: DC link precharge failure

Likely causes

• Too many SVM and/or SVPM units connected
• DC link short-circuited
• Recharge current limiting resistor defective

First checks, in this order

1. Check the connected units against the SVPM specification
2. With power off and the charge LED out, check the DC link connections for a short
3. If both are fine, replace the distributing board as the manual directs

Converter: control power supply undervoltage (βi SVPM: STATUS2 '-' with STATUS1 'b1')

What it means: The SVPM control power supply voltage has dropped.^[4]

On the CNC screen: 432 (servo) / 9111 (spindle): Converter: control power supply undervoltage

Likely causes

• Low control power input voltage
• Supply dips

First checks, in this order

1. Measure the control power input to the SVPM
2. Check the incoming supply for dips

Converter: DC link overvoltage (βi SVPM: STATUS2 '-' with STATUS1 '11')

What it means: In the SVPM main circuit, the DC link voltage is abnormally high.^[4]

On the CNC screen: 439 (servo) / 9011 (spindle): Converter: DC link overvoltage

Likely causes

• Excessive regenerated power for the SVPM capacity
• AC source output impedance too high
• Main power switched off while the emergency stop was released

First checks, in this order

1. Check the SVPM is sized for the load
2. Check source impedance: normal if the voltage variation at maximum output is within 7 percent
3. Check the power-off sequence

Converter: input open phase (βi SVPM: STATUS2 '-' with STATUS1 '04')

What it means: The SVPM input power supply is abnormal because a phase is open.^[4]

On the CNC screen: 607 (servo) / 9004 (spindle): Open phase in the converter main power supply

Likely causes

• Missing phase on the incoming supply
• Loose or broken input connection

First checks, in this order

1. Measure all three input phase voltages
2. If the voltages are fine, check the input connections

βi SV alarm (ALM LED) (βi SV: yellow ALM LED lit (no 7-segment display))

What it means: The stand-alone βi SV only lights its ALM LED on any alarm, so the CNC alarm number tells you which fault it is.^[4]

On the CNC screen: Read the CNC number (Series 16i family shown, Series 15i uses SV0 plus the same number): 433 DC link undervoltage, 439 DC link overvoltage, 440 excessive deceleration power, 432 control power undervoltage, 444 internal fan, 601 radiator fan, 449 IPM alarm, 603 IPM alarm (OH), 438 motor current alarm

Likely causes

• Any of the converter or inverter faults listed for the βi SV (DC link voltage, fans, IPM, motor current)
• FSSB connector, cable, SVM or CNC failure (FSSB communication error also lights ALM)

First checks, in this order

1. Read the alarm number on the CNC alarm screen and the servo adjustment screen
2. Match it to the βi SV list in B-65325EN Part I chapter 2 and follow that procedure
3. Most procedures include pushing the faceplate (control PCB) fully home before replacing the SVM

External 24 VDC control power low (βi SV: ALM LED with CNC 432)

What it means: On the βi SV the external 24 VDC control power supply voltage is low.^[4]

On the CNC screen: SV0432 (Series 15i) / 432 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: control power supply undervoltage

Likely causes

• Drop in the external 24 V control power supply
• CXA19A or CXA19B connector or cable defective
• SVM failure

First checks, in this order

1. Measure the external 24 VDC supply (normal is 21.6 V or higher)
2. Check the CXA19A and CXA19B connectors and cable
3. Replace the SVM

DC link overvoltage (βi SV) (βi SV: ALM LED with CNC 439)

What it means: On the βi SV the DC link voltage in the main circuit is abnormally high.^[4]

On the CNC screen: SV0439 (Series 15i) / 439 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: DC link overvoltage

Likely causes

• No regenerative resistor fitted on SVM1-4i or SVM1-20i
• Excessive regenerated power from short acceleration and deceleration times
• Faceplate not fully seated or SVM failure

First checks, in this order

1. On SVM1-4i and SVM1-20i, use a regenerative resistor
2. Increase the acceleration and deceleration time constant; if the alarm becomes rarer, regeneration capacity is short, so set a time constant that stops the alarm
3. Push the faceplate fully home, then replace the SVM

Excessive deceleration power (βi SV) (βi SV: ALM LED with CNC 440)

What it means: The βi SV converter deceleration (regenerative) power is too large.^[4]

On the CNC screen: SV0440 (Series 15i) / 440 (Series 16i, 18i, 20i, 21i, 0i, Power Mate i): Converter: excessive deceleration power

Likely causes

• Regenerative resistor circuit open: missing dummy connector or a resistor connection problem on CXA20
• Average regenerative power too high
• Abnormal regenerative discharge circuit or SVM failure

First checks, in this order

1. Without a separate resistor: fit the dummy connector on CXA20 (SVM1-4i, SVM1-20i) or on CXA20 and CZ6 (SVM1-40i, SVM1-80i with built-in resistor)
2. With a separate resistor: check the resistance across CXA20 on the resistor side reads 0 ohm
3. Reduce acceleration and deceleration frequency or review the resistor specification
4. Push the faceplate fully home, then replace the SVM