FANUC SP9058 Alarm 58: Converter Main Circuit Overload and Troubleshooting

FANUC SP9058 means that the main-circuit heat sink or radiator in the common Power Supply has reached an abnormally high temperature. The CNC displays SP9058, usually with the message CNV. OVERLOAD; the spindle amplifier indication is 58, and the associated Power Supply (PS) displays 3 on the systems covered by the cited FANUC manuals.

FANUC's documented troubleshooting sequence is to check the Power Supply cooling condition, inspect the main-circuit cooling fan, remove dust from the cooling system, review the operating load, confirm that the control printed-circuit board is seated correctly, and replace the Power Supply only if the alarm remains after those checks.

For the surrounding serial spindle alarms, see the FANUC Spindle Alarm Codes SP9034–SP9092.

What Does FANUC SP9058 Mean?

The Power Supply converts the incoming AC power and supplies the DC link used by connected spindle and servo amplifiers. Power semiconductors in this main circuit produce heat during operation. A radiator or heat sink transfers that heat to the cooling airflow.

SP9058 is generated when the Power Supply detects that the main-circuit heat-sink temperature has risen beyond its allowable condition. FANUC summarizes the alarm as Converter: main circuit overload and directs technicians to the Power Supply alarm-code-3 procedure.

The alarm does not automatically prove that the Power Supply electronics have failed. FANUC lists four principal areas to check:

• A broken or stopped main-circuit cooling fan

• Dust accumulation in the cooling system

• Excessive operating load

• Poor installation of the Power Supply control printed-circuit board

These causes must be evaluated before replacing the complete Power Supply.

SP9058 Is Not Limited to Differential Speed Mode

Some translated alarm descriptions incorrectly add the phrase “in differential speed mode.” FANUC's English alarm table does not define SP9058 as a differential-spindle-control alarm. It identifies an abnormal temperature rise in the radiator of the Power Supply.

Differential speed and spindle synchronization have their own alarm numbers, such as SP9049 and SP9050. SP9058 can occur on any applicable configuration when the converter heat sink becomes too hot, regardless of whether differential speed control is active.

This distinction prevents technicians from spending time on spindle gear-ratio or differential-speed parameters that are unrelated to the detected temperature condition.

How the Power Supply Cooling System Works

The heat sink provides a path for heat to leave the power semiconductors. A cooling fan moves air through or across the radiator fins. The system depends on several conditions being correct at the same time:

• The fan must rotate at the required speed and in the correct direction.

• The fan connector and power supply must be reliable.

• Radiator fins and air passages must remain open.

• Cabinet intake and exhaust paths must not be blocked.

• Ambient temperature must remain within the equipment specification.

• The electrical load must remain within the Power Supply rating.

• The control board and temperature-detection circuit must be connected correctly.

A weakness in any one of these areas can reduce cooling capacity. For example, a fan may still rotate but provide inadequate airflow because it is slow, contaminated, installed backward, or drawing already-heated cabinet air.

1. Confirm SP9058, Amplifier 58, and Power Supply 3

Before switching off the machine, record every active alarm display:

• Confirm SP9058 or CNV. OVERLOAD on the CNC.

• Confirm 58 on the spindle amplifier display.

• Confirm 3 on the common Power Supply display.

• Record any simultaneous servo or spindle alarms.

• Note whether the alarm appeared during cutting, rapid movement, acceleration, deceleration, idle operation, or power-up.

Also record:

• Complete CNC series and model

• Complete Power Supply part number and every suffix

• Connected servo and spindle amplifier models

• Power Supply width and cooling-fan arrangement

• Cabinet ambient temperature

• Program and machine operation at the time of the alarm

• Any recent fan, drive, board, filter, cabinet, or machine-load changes

Do not diagnose the alarm from the CNC message alone. The combination of SP9058 / 58 / 3 distinguishes this condition from neighboring cooling and regenerative alarms.

2. Determine When the Alarm Occurs

The alarm timing can quickly narrow the investigation.

This table provides diagnostic guidance. It does not replace the model-specific FANUC maintenance procedure.

3. Review the Operating Load

FANUC lists overload as a cause of Power Supply alarm 3 and instructs technicians to examine the operating conditions. Because the Power Supply can feed multiple servo and spindle amplifiers, the relevant condition is not necessarily limited to spindle cutting load alone.

Review:

• Spindle load during cutting

• Acceleration and deceleration frequency

• Simultaneous movement of multiple servo axes

• Repeated rapid traverse cycles

• Spindle starts, stops, and reversals

• Increased tool engagement or cutting depth

• A heavier chuck, fixture, or workpiece

• Mechanical drag in the spindle or axes

• A recently shortened production cycle

• Motors or amplifiers recently changed to a different specification

Compare the machine's current behavior with a known-good cycle. If the alarm began after a process change, use a controlled test to reduce cutting load or the number of simultaneous high-load operations. Any permanent program or parameter adjustment must remain within the machine builder's approved limits.

Do not assume that lowering the spindle speed alone will solve the problem. A mechanically binding axis, high acceleration duty, failed fan, or obstructed radiator can overheat the Power Supply even when the commanded spindle speed appears moderate.

4. Inspect the Main-Circuit Radiator Cooling Fan

FANUC's Power Supply alarm-code-3 procedure begins with the main-circuit cooling fan. Confirm whether every fan fitted to the installed Power Supply is operating correctly.

The illustrated arrangements show that fan size, quantity, mounting screws, and connector position vary with Power Supply width. The 60 mm/90 mm, 150 mm, and 300 mm examples must not be treated as interchangeable parts diagrams. Always identify the exact Power Supply model before ordering or installing a fan.

Check:

• Whether every required fan rotates

• Whether the fan reaches normal speed

• Correct fan supply voltage

• Fan connector seating and contact condition

• Broken, pinched, or heat-damaged wiring

• Dust, oil mist, or foreign material obstructing the blades

• Bearing noise, vibration, or intermittent stopping

• Correct airflow direction

• Correct mounting screws and fan orientation

• Hot-air recirculation around the cabinet or radiator

If a fan is stopped, first isolate power and check its connector and wiring. Replace it with the exact specified cooling fan when it is confirmed defective. Do not select a replacement only by frame size or voltage; airflow, connector, speed detection, direction, and mounting can differ.

After replacement, verify that the fan is installed in the documented direction. A fan running backward can appear functional while reducing or reversing the intended airflow.

5. Clean the Heat Sink and Cooling Path

FANUC lists dust accumulation as a direct cause of Power Supply alarm 3. Inspect the Power Supply radiator, rear heat-sink fins, fan guard, cabinet filters, air ducts, and the space around the drive stack.

Look for:

• Dust packed between radiator fins

• Oil mist forming a sticky insulating layer

• Chips or debris at air inlets

• Clogged cabinet filters

• Blocked exhaust openings

• Cable bundles restricting the fan intake

• Insufficient clearance behind the Power Supply

• A cabinet panel or duct installed incorrectly

Clean the cooling system only with the method permitted by the machine and FANUC manuals. FANUC refers to using a vacuum cleaner or factory air blower. If compressed air is permitted, prevent contamination from being driven deeper into connectors, boards, or adjacent equipment. Do not spin an unpowered fan at excessive speed with an air jet.

Cleaning only the visible fan guard may not restore cooling if the radiator fins behind the Power Supply remain blocked. Inspect the complete path from cabinet intake to exhaust.

6. Check Cabinet Temperature and Ventilation

Although the alarm is detected at the Power Supply heat sink, high cabinet temperature reduces the temperature difference available for cooling. Verify:

• Cabinet intake-air temperature

• Air conditioner or heat exchanger operation

• Cabinet circulation fans

• Filter condition

• Door seals and panel installation

• Exhaust temperature

• Heat from neighboring drives, transformers, or braking components

• Required clearance around the FANUC drive stack

Measure temperature under the same operating condition that produces SP9058. A cabinet that feels acceptable when idle may become too hot during a long production cycle.

Do not run permanently with the cabinet door open as a repair. An open door can change airflow, allow contamination to enter, defeat the enclosure design, and expose dangerous voltage. It may be used only if the machine builder's controlled diagnostic procedure explicitly permits it.

7. Verify the Control Printed-Circuit Board Installation

FANUC identifies poor installation of the Power Supply control printed-circuit board as another cause of alarm 3. A partially detached connector between the control board and power board can interfere with temperature monitoring or fan-related signals.

With machine power isolated and the DC link fully discharged according to the applicable manual:

• Inspect whether the Power Supply faceplate is fully seated.

• Confirm the control printed-circuit board is installed to its mechanical stop.

• Check for loose retaining hardware.

• Inspect accessible connectors for damage or partial engagement.

• Look for evidence that the board was recently removed or replaced.

Do not interpret this instruction as permission to remove or reseat the board while energized. High DC-link voltage can remain after incoming power is switched off. Qualified personnel must follow the specified discharge time and verify a safe condition before touching the drive.

The technician note refers to checking the “side plate.” FANUC's English procedure is more specific: it calls for confirming the control printed-circuit board/faceplate installation. Follow the construction of the exact Power Supply rather than pulling an unrelated side cover.

8. Test the Fan and Temperature Pattern

After visual checks, use a controlled machine-builder-approved test to determine whether cooling is restored. Record:

• Cabinet intake temperature before startup

• Time from startup to SP9058

• Power Supply and spindle load pattern

• Fan operation throughout the cycle

• Whether the alarm occurs at the same program block

• Whether cleaning or fan replacement changes the time to alarm

A longer time to alarm after cleaning indicates improved thermal performance but does not necessarily prove the system is within specification. The machine must complete its required duty cycle without exceeding the Power Supply limits.

If available through the machine's approved diagnostics, compare load and temperature-related information with a known-good machine of the same configuration. Do not connect unapproved probes to the Power Supply or defeat the temperature protection circuit.

9. Replace the Power Supply Only After Cooling Checks Pass

The SP9058 alarm list includes Power Supply replacement after checking the cooling condition. Replacement becomes reasonable when:

• The correct fans operate normally.

• Airflow direction and fan specification are correct.

• Radiator fins and cabinet filters are clean.

• Ambient temperature is within specification.

• Operating load is within the machine and Power Supply ratings.

• The control printed-circuit board is fully seated.

• Connectors and wiring are normal.

• SP9058 / 58 / 3 still returns under a controlled test.

At that point, the Power Supply's temperature sensing, control board, power semiconductor interface, or other internal circuitry may be abnormal. Use the exact model-specific FANUC procedure to determine whether the control board or complete Power Supply should be replaced.

Before installing a replacement, verify the full FANUC part number and every suffix, input-voltage class, capacity, connected amplifier combination, software compatibility, cooling arrangement, connector layout, and machine-builder requirements.

If replacement or repair is required, browse FANUC servo, spindle, and power drives or send the complete Power Supply model to REACO CNC for compatibility checking.

Difference Between SP9057, SP9058, and SP9059

These neighboring alarms involve the converter/common Power Supply, but they identify different conditions.

Do not treat every converter temperature alarm as the same fault. SP9057 focuses on the regenerative resistor circuit, while SP9058 focuses on the main-circuit heat sink. SP9059 directly reports a stopped Power Supply cooling fan under the applicable alarm definition.

SP9058 Is Not the Same as a Motor Overload

SP9058 can be triggered by operating load, but its detected condition is Power Supply heat-sink overtemperature. A motor thermal alarm, spindle current overload, or mechanical overload uses a different alarm number and detection path.

If the machine also reports a motor or spindle overload alarm, diagnose both numbers and determine whether one condition caused the other. Do not replace a motor solely because SP9058 is displayed, and do not replace the Power Supply solely because cutting load is high.

What Not to Do With SP9058

• Do not repeatedly reset the alarm and resume heavy operation without restoring cooling.

• Do not assume the alarm applies only to differential spindle control.

• Do not replace the common Power Supply before checking its fans, radiator, load, and board seating.

• Do not install a fan based only on width or physical appearance.

• Do not reverse the fan airflow direction.

• Do not clean energized equipment.

• Do not remove the Power Supply faceplate until the DC link is safely discharged.

• Do not bypass the temperature sensor or fan protection circuit.

• Do not leave the cabinet door open as a permanent cooling solution.

• Do not use water, conductive cleaner, or an uncontrolled high-pressure air jet on the drive electronics.

FANUC SP9058 Diagnostic Table

Recommended Troubleshooting Order

1. Confirm SP9058 on the CNC, 58 on the spindle amplifier, and 3 on the Power Supply.

2. Record the exact cycle step, load, cabinet temperature, and time to alarm.

3. Identify the complete Power Supply model, suffix, width, and fan arrangement.

4. Check whether every main-circuit radiator fan operates at normal speed and in the correct direction.

5. Inspect fan connectors, wiring, mounting, and airflow.

6. Clean the radiator fins, fan guards, filters, and cabinet air path.

7. Verify cabinet cooling and ambient temperature under production conditions.

8. Review spindle, servo, acceleration, and simultaneous-axis load.

9. Isolate power, observe the required discharge time, and confirm the Power Supply control board/faceplate is fully seated.

10. Retest using the machine builder's approved procedure.

11. If the alarm remains after all external causes are eliminated, repair or replace the exact compatible Power Supply.

12. If a different alarm appears, diagnose that number separately.

Technical References

• FANUC Series 0i-MODEL D / Series 0i Mate-MODEL D Maintenance Manual, B-64305EN/03, SP9058 / Amplifier Indication 58

• FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Power Supply Alarm Code 3 (αiPS)

• FANUC Servo Amplifier αi Series Descriptions, B-65282EN series, Power Supply radiator cooling fan installation and replacement

Always use the English manual edition that applies to the exact CNC, Power Supply, connected amplifiers, fan arrangement, and machine-builder configuration.

Need Help With FANUC SP9058 Alarm 58?

REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC power supplies, spindle amplifiers, servo amplifiers, and cooling components. Send the CNC alarm screen, spindle amplifier display, Power Supply display, complete part numbers and suffixes, fan photos, cabinet temperature, and details of when the alarm occurs.

Visit the FANUC Technical Support Center for additional FANUC alarm guidance, or contact REACO CNC for assistance.

Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The correct cooling-fan model, airflow direction, board procedure, load limit, and replacement Power Supply depend on the exact drive hardware and machine configuration.