FANUC SP9111 means that the converter or common power-supply control voltage is too low. The CNC displays SP9111, the spindle amplifier can display b1/B1, and a separate FANUC αi Power Supply normally displays alarm 6.
SP9111 is reported through the spindle alarm path, but it does not automatically prove that the spindle amplifier is defective. On an amplifier group with a separate αi Power Supply, FANUC's official procedure directs the technician to check the incoming control power and replace the Power Supply if the alarm occurs as soon as control power is switched on. On an integrated βi SVPM or βi SVSP system, the converter is part of the combined amplifier, so replacement of that integrated unit may be required.
| Alarm item | Display or condition | Meaning |
|---|---|---|
| CNC alarm | SP9111 | Converter control-power undervoltage was reported |
| Spindle amplifier display | b1 / B1 | The amplifier received the common converter alarm |
| Separate αi Power Supply display | 6 | The Power Supply detected low internal control voltage |
| Main official causes | Low input voltage or failed Power Supply | Verify the supply before replacing hardware |
| Integrated βi system | b1 on the SVPM/SVSP | The converter and spindle amplifier are combined in one unit |
For nearby spindle and converter alarm numbers, see the FANUC Spindle Alarm Codes SP9034–SP9092 and Related Amplifier Alarms.
What Does FANUC SP9111 Mean?
FANUC describes SP9111 as “Converter: control power supply low voltage.” In an αi amplifier group, the Power Supply generates control power used by the connected servo and spindle amplifiers. If that control voltage falls below the permitted level, the Power Supply reports alarm 6 and the spindle system reports SP9111 with b1.
The αi maintenance manual describes alarm 6 more specifically as an abnormal 24-V supply inside the Power Supply and notes that an internal fuse may have opened. The listed causes are:
- A decrease in the control-power input voltage
- A defective Power Supply
This is different from a low DC-link alarm, a motor-power phase loss, a spindle motor fault, or a spindle feedback problem. The exact module that must be replaced depends on whether the machine uses a separate Power Supply or an integrated converter/amplifier.
Why SP9111 Can Appear as a Spindle Alarm When the Power Supply Is Faulty
In an αi amplifier group, the Power Supply is connected to servo and spindle amplifiers through the amplifier-group connection. Power-supply status information is transferred to the CNC through the designated power-supply control axis. If that control axis is a spindle axis, a Power Supply alarm can therefore appear in the CNC as an SP alarm.
The alarm path can be summarized as follows:
| Device | Typical indication | Diagnostic role |
|---|---|---|
| CNC | SP9111 | Reports the converter alarm through the spindle channel |
| Spindle amplifier | b1 / B1 | Relays the common converter control-power fault |
| αi Power Supply | 6 | Identifies the originating Power Supply condition |
Always inspect every module display. Replacing the spindle amplifier only because the CNC prefix is SP can leave the actual Power Supply fault unchanged.
Separate αi Power Supply vs. Integrated βi Amplifier
The correct replacement target depends on the installed hardware architecture.
| FANUC hardware arrangement | Where the converter is located | Likely replacement after input power is confirmed |
|---|---|---|
| Separate αiPS or αiPSR with spindle and servo amplifiers | In the standalone Power Supply module | Replace the failed Power Supply or the approved service component specified by the exact manual |
| Integrated βi SVPM or βi SVSP | Inside the combined power/servo/spindle unit | Replace the integrated SVPM/SVSP if the alarm occurs at control-power startup and the input is correct |
| Unknown or mixed installation | Must be identified from the complete FANUC model numbers | Do not order a module until the architecture and suffixes are confirmed |
This distinction explains why a brief service note may say “replace the spindle amplifier” while the αi Power Supply manual says “replace the Power Supply.” Both statements can only be evaluated against the exact amplifier family installed in the machine.
1. Confirm SP9111, b1, and Power Supply Alarm 6
Before disconnecting any hardware, record all displays:
- The CNC shows SP9111.
- The spindle or integrated amplifier shows b1/B1.
- A separate αi Power Supply, when fitted, shows 6.
- The Power Supply display is not blank.
- No additional DC-link, phase-loss, communication, fuse, or emergency-stop alarm is present.
Also record:
- Complete CNC series and model
- Complete Power Supply model and every suffix
- Complete spindle and servo amplifier models and suffixes
- Whether the hardware is αiPS/αiPSR, βi SVPM, βi SVSP, or another family
- All status-display codes at the same time
- Whether the alarm appears immediately at power-up or only after operation begins
- Any recent power-supply, cable, transformer, amplifier, or cabinet work
If the Power Supply display is blank rather than showing 6, follow the no-display procedure for that module. A blank display can mean that control power is absent, the control-power cable is defective, the control circuit has failed, or the downstream 24-V path is shorted. It is not the same diagnostic condition as a confirmed alarm 6.
2. Determine When the Alarm Occurs
The timing of SP9111 helps separate an external supply problem from an internal module fault.
| When SP9111 occurs | Checks to prioritize |
|---|---|
| Immediately when control power is switched on | Incoming control voltage, connector condition, correct module wiring, and failed Power Supply or integrated amplifier |
| After a recent module replacement | Model compatibility, connector positions, wiring, and installation errors |
| Intermittently during operation | Input-voltage dips, loose terminals, failing contacts, vibration, or a deteriorating control-power circuit |
| When another machine load starts | Upstream control transformer or power source capacity, voltage sag, and shared supply connections |
| After cabinet work | Loose plug, damaged conductor, incorrect reconnection, or shorted control-power path |
| Power Supply display is blank | Missing control input or shorted control-power circuit; diagnose the no-display condition first |
FANUC specifically states that if alarm 6 is issued merely by turning on control power, the Power Supply is a replacement candidate after the input voltage has been checked.
3. Check the Incoming Control-Power Supply
FANUC lists reduced input voltage as the first cause of alarm 6/b1. A qualified technician should verify the control-power source at the module while the fault is present and compare the reading with the maintenance manual for the exact hardware.
Check:
- The control-power circuit breaker, fuses, and disconnect devices
- The machine control transformer or external control-power supply
- Input terminals and connectors for looseness, heat damage, oxidation, or contamination
- Supply voltage before startup and while the amplifier group is energized
- Voltage dips when contactors, pumps, fans, or other heavy loads operate
- Correct wiring after transformer, cabinet, or amplifier service
- The machine's grounding and protective-bonding arrangement
Do not apply one universal voltage value to every FANUC generation. For example, the αiPS/αiPSR procedure in B-65285EN/04 uses 200-VAC control power at CX1A, while integrated and later amplifier families can use a different supply arrangement. Use the model-specific connection manual and machine electrical drawing.
If the input voltage is low, repair the upstream supply problem before replacing any FANUC module. A new Power Supply will not correct a weak transformer, failing contact, open fuse holder, loose terminal, or undersized external source.
4. Inspect the Control-Power Connections
With machine power isolated and the specified DC-link discharge time observed, inspect the complete control-power path.
Look for:
- A connector that is not fully inserted or locked
- Bent, recessed, oxidized, or overheated contacts
- Broken conductors near connector strain reliefs
- A crushed, stretched, cut, or contaminated cable
- Incorrect wiring after a module was replaced
- Loose terminal screws or discolored terminal blocks
- Nonstandard splices or substituted cables
- Conductive coolant, oil, or metal dust inside connectors
Photograph and label the original connections before removal. Do not disconnect or reconnect amplifier-group cables while power is applied.
5. Check for a Shorted or Overloaded Shared Control-Power Path
On systems where the Power Supply distributes control power to connected amplifiers, a downstream module or cable fault can pull down the shared control supply. FANUC's αi no-display procedure uses controlled cable isolation and sequential reconnection to identify an amplifier that shorts the 24-V path.
Because the connector arrangement varies by amplifier generation, perform isolation only with the exact maintenance procedure and machine electrical drawing. In general, the result is interpreted as follows:
| Controlled test result | Interpretation |
|---|---|
| Correct input is present and alarm 6 remains with the approved external loads isolated | The Power Supply itself is strongly indicated |
| Alarm disappears when one approved downstream branch is isolated | That cable or connected amplifier may be shorting or overloading the control supply |
| Alarm follows movement of a cable or connector | An intermittent conductor or contact is likely |
| Input voltage collapses before the FANUC module | The upstream control-power source or wiring is defective |
Do not improvise by unplugging modules one at a time with the machine energized. The DC link can retain lethal voltage after incoming power is removed, and an incorrect reconnection can damage multiple amplifiers.
6. Evaluate the Internal 24-V Supply and Fuse Condition
For αiPS and αiPSR units, FANUC identifies an abnormal internal 24-V supply and a possible internal fuse opening as the meaning of alarm 6. This points to a fault inside the Power Supply after the input and external control-power path have been confirmed.
An opened internal fuse is evidence of a fault, not automatically the root cause. Before replacing any serviceable fuse or board, determine whether the cause is:
- An internal Power Supply failure
- A downstream short circuit
- Incorrect external wiring
- A damaged cable or connector
- An unauthorized external connection to the control-power circuit
Use only the fuse, control board, and replacement procedure specified for the complete FANUC model. Do not install a higher-rated fuse or bridge the protection device.
7. Replace the Correct Module
If the input power, wiring, connectors, and permitted external-load checks are normal, replace the hardware identified by the applicable manual:
- Separate αiPS/αiPSR system: Replace the defective Power Supply or the supported control printed-circuit board if the exact FANUC service procedure permits board-level replacement.
- Integrated βi SVPM/SVSP system: Replace the combined unit when the correct input is present and b1 occurs at control-power startup.
- Downstream short confirmed: Replace the identified cable, servo amplifier, or spindle amplifier that is pulling down the shared control supply.
Before ordering a replacement, verify:
- Complete FANUC order specification
- Every model suffix
- Input-voltage class
- Rated capacity
- Hardware generation
- Connector arrangement
- Supported control-board and software combination
- Machine-builder approved supersession information
Do not select a replacement by appearance, base model, or output rating alone. Browse FANUC servo, spindle, and power drives or send REACO CNC the complete labels for a compatibility check.
8. Retest the Amplifier Group
After the approved repair:
- Restore every connector, protective cover, ground, and cable clamp.
- Confirm that no tools or loose conductors remain in the cabinet.
- Apply control power according to the machine-builder procedure.
- Confirm that the Power Supply reaches its normal status without alarm 6.
- Confirm that b1/B1 and SP9111 no longer appear.
- Check every servo and spindle amplifier display.
- Release emergency stop and enable the main circuit according to the normal sequence.
- Test the spindle and axes under controlled conditions.
- Monitor the control-power voltage for recurring dips.
- If another alarm appears, diagnose the newly displayed number separately.
Difference Between SP9110, SP9111, SP9112, and SP9113
| CNC alarm | Amplifier display | Power Supply display | FANUC description | Main diagnostic area |
|---|---|---|---|---|
| SP9110 | b0 / B0 | Configuration-dependent | Communication error between amplifiers | Amplifier-group communication connectors, cables, and modules |
| SP9111 | b1 / B1 | 6 | Converter control power supply low voltage | Control-power input, shared control-power path, and Power Supply |
| SP9112 | b2 / B2 | 8 | Converter excessive regenerative power | Regenerative energy, deceleration, and Power Supply capacity |
| SP9113 | b3 / B3 | A | Converter radiator cooling fan stopped | Power Supply cooling fan, airflow, and board installation |
Confirm all available displays. The b-series spindle indication reports a common converter condition; the Power Supply code identifies the originating alarm more precisely.
Do Not Confuse Power Supply Alarm 6 With Servo Amplifier Alarm 6
The number 6 has different meanings depending on which module displays it.
| Display location | Code | Meaning |
|---|---|---|
| αi Power Supply | 6 | Control power supply voltage decrease; associated with SP9111/b1 |
| Servo amplifier inverter display | 6 | Inverter overheat on applicable hardware |
| CNC spindle alarm | SP9111 | Converter control-power undervoltage reported through the spindle channel |
Always identify the physical module displaying the code before using an alarm table. Diagnosing every code 6 as SP9111 can lead to the wrong repair.
FANUC SP9111 Diagnostic Table
| Finding | Likely interpretation | Recommended action |
|---|---|---|
| CNC shows SP9111, spindle amplifier shows b1, and αiPS shows 6 | Common Power Supply control voltage is low | Check the control-power input, then diagnose or replace the Power Supply |
| Alarm appears immediately at control-power startup with correct input | Internal Power Supply or integrated converter fault is likely | Replace the correct module specified for the installed family |
| Measured input is below specification | External supply problem is causing the alarm | Repair the transformer, supply, breaker, fuse, wiring, or connection |
| Alarm occurs when another machine load starts | Control-power voltage may be sagging | Measure under load and inspect source capacity and shared connections |
| Power Supply display is blank | Control power may be absent or the distributed control supply may be shorted | Follow the model-specific no-display procedure |
| Alarm disappears when an approved downstream branch is isolated | Connected cable or amplifier may be pulling the control voltage down | Test the identified branch and replace the defective item |
| Integrated βi SVPM/SVSP shows b1 | Converter is inside the combined unit | Check the input supply and replace the integrated unit if confirmed defective |
| Servo amplifier alone displays 6 | This may be an inverter overheat code, not Power Supply alarm 6 | Use the servo-amplifier alarm procedure for that display |
| A replacement unit has a different suffix | Compatibility is unconfirmed | Verify the complete specification before power-up |
Recommended Troubleshooting Order
- Confirm SP9111 on the CNC, b1/B1 on the amplifier, and 6 on a separate Power Supply when fitted.
- Photograph and record every simultaneous alarm and status display.
- Identify whether the machine uses a separate αi Power Supply or an integrated βi SVPM/SVSP.
- Record the complete models and suffixes of all modules in the amplifier group.
- Determine whether the alarm occurs immediately, intermittently, under load, or after service work.
- Check the incoming control-power voltage against the exact FANUC and machine specifications.
- Inspect breakers, fuses, transformers, terminals, connectors, and cables.
- Correct any low-voltage, loose-connection, or wiring problem found upstream.
- With power isolated, inspect the shared control-power path for damage or a short circuit.
- Use only the approved isolation procedure to identify a downstream module that pulls the supply low.
- If the correct input is present and alarm 6/b1 remains at startup, replace the applicable Power Supply or integrated amplifier.
- Verify full replacement compatibility before installation.
- Restore all wiring and protective hardware, then retest the complete amplifier group.
What Not to Do With SP9111
- Do not replace the spindle amplifier solely because the CNC alarm begins with SP.
- Do not confuse Power Supply alarm 6 with servo-amplifier alarm 6.
- Do not assume every FANUC generation uses the same control voltage or connector.
- Do not disconnect amplifier-group cables while power is applied.
- Do not approach the DC link until the specified discharge time has passed and zero voltage has been verified.
- Do not replace an internal fuse without investigating why it opened.
- Do not install a higher-rated fuse or bypass a protective device.
- Do not change spindle parameters to clear a control-power hardware alarm.
- Do not repeatedly reset the machine while the input supply is unstable.
- Do not order a replacement from only the base model number.
Technical References
- FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, SP9111 and Power Supply Alarm Code 6
- FANUC AC Servo Motor βis/βi Series, AC Spindle Motor βi Series, Servo Amplifier βi Series Maintenance Manual, B-65325EN series, STATUS1 Alarm Code b1 / SP9111
- Applicable FANUC connection manual and machine-builder electrical documentation for the installed control-power input, connector arrangement, isolation method, and discharge procedure
Always use the manual edition that applies to the exact CNC, Power Supply, spindle amplifier, servo amplifier, integrated amplifier, hardware generation, and machine.
Need Help With FANUC SP9111 Alarm?
REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC power supplies, spindle amplifiers, servo amplifiers, integrated βi amplifiers, control boards, and cables. Send us the CNC alarm screen, every amplifier and Power Supply display, complete module models and suffixes, cabinet photos, input-voltage readings, and details of when SP9111 occurs.
Browse FANUC servo, spindle, and power drives, visit the FANUC Technical Support Center, or contact REACO CNC for assistance.
Reference Source: FANUC technical documentation. The correct input-voltage check, connector names, isolation method, serviceable components, and replacement target depend on the installed amplifier family and machine-builder design.
