FANUC SP9019 Alarm 19: U-Phase Current Offset Causes and Troubleshooting

FANUC SP9019 indicates that the offset voltage in the spindle amplifier's U-phase current detection circuit is excessively high. On systems that use this CNC alarm mapping, the CNC displays SP9019, while the spindle amplifier displays alarm 19.

FANUC maintenance manuals state that the offset check is performed when power is turned on. For an αi spindle amplifier module, the standard action is to replace the spindle amplifier. If alarm 19 appears immediately after its control printed-circuit board was replaced, check the connectors between the power unit and the control board. For a βiSVSP, FANUC instructs technicians to check that the control board is mounted correctly and to replace the βiSVSP if the board is already mounted correctly.

For the surrounding alarm numbers, see the FANUC Serial Spindle Alarm Codes SP9001–SP9033.

What Does FANUC SP9019 Mean?

The spindle amplifier uses current-detection circuitry to monitor motor phase current. Alarm 19 means that the internal offset voltage associated with the U-phase current detection circuit is outside the permitted range during the amplifier's power-on check.

This distinction matters: SP9019 does not mean that excessive operating current is flowing through the motor's U phase. It means that the detection circuit's offset is abnormal before normal spindle operation begins. Therefore, SP9019 should not automatically be diagnosed as a heavy cutting load, rapid acceleration, a stalled spindle, or a shorted motor winding.

FANUC pairs alarm 19 with alarm 20:

The troubleshooting principle is similar, but always diagnose the phase and alarm number actually displayed.

The Check Is Performed at Power-On

FANUC B-65285EN/04 and B-65325-series maintenance manuals specify that the current-detection offset check is made when power is turned on. SP9019 will therefore normally appear during amplifier initialization rather than after a period of cutting.

Record whether the alarm appears:

• Every time the machine is powered on

• Intermittently during startup

• Immediately after the spindle amplifier control board was removed or replaced

• After the complete spindle amplifier was repaired, transported, or reinstalled

This timing helps determine whether board installation or connector contact requires inspection. It does not change the official meaning of alarm 19.

Do not repeatedly cycle power as a repair. An intermittent alarm can still indicate an unreliable internal connection or a failing current-detection circuit.

1. Confirm SP9019 and Amplifier Alarm 19

Before removing hardware, confirm the alarm at both locations where possible:

• The CNC reports SP9019 or an equivalent serial-spindle alarm for the installed control series.

• The spindle amplifier status display shows 19.

• The displayed number is not 12, 20, 22, or another current-related alarm.

Record the CNC alarm screen and the amplifier display before turning off power. Also record:

• The complete CNC series and model

• The full spindle amplifier, SPM, SVPM, or βiSVSP part number, including every suffix

• The control printed-circuit board number when it can be identified safely

• Whether the alarm started after board or amplifier service

• Whether the control board, power unit, or internal connectors were recently disturbed

The CNC-side alarm number is not identical across every FANUC generation. Depending on the CNC and spindle system, FANUC documentation maps amplifier alarm 19 to SP9019, SP098x, SP12xx, alarm 750, or another serial-spindle indication. The amplifier display 19 and the applicable manual are the most reliable diagnostic references.

2. Isolate Power Before Inspecting the Amplifier

Do not insert, remove, or press a spindle amplifier control board while power is applied.

Before opening the electrical cabinet or touching the amplifier:

• Place the machine in the required safe state.

• Switch off and isolate the power supply.

• Wait for the DC link to discharge for the period specified in the applicable FANUC manual.

• Confirm that the charge indicator is off and verify the required electrical condition.

• Follow the machine builder's lockout and electrical-safety procedure.

FANUC amplifiers can retain hazardous voltage after incoming power is switched off. Internal inspection, board removal, and amplifier replacement must be performed by qualified personnel.

3. Check the Control Board Installation When Applicable

The correct board check depends on the installed amplifier series and the repair history.

For an αi SPM, FANUC states that if alarm 19 occurs immediately after the SPM control printed-circuit board was replaced, technicians should check the plugging of the connectors between the power unit and the SPM control board.

For a βiSVSP, FANUC's procedure is broader: check whether the control printed-circuit board is mounted correctly. If it is mounted correctly, replace the βiSVSP.

Where this inspection applies, check for:

• A control board or faceplate that is not inserted fully

• Uneven seating or loose mounting hardware

• Misaligned or partially engaged board-to-power-unit connectors

• Bent, contaminated, corroded, or visibly damaged connector contacts

• Damage resulting from previous removal, repair, transportation, or installation

If the board is not seated correctly, remove and reinstall it only according to the maintenance procedure for the exact amplifier model. Do not force the board, bend connector pins, bypass the detection circuit, or exchange boards between amplifiers without confirming part number and compatibility.

The technician's practice of removing and reinserting the board is therefore valid for applicable hardware and connection conditions, but it should not be presented as a universal cure for every SP9019 alarm. If there has been no recent board work, or if the board and connectors are confirmed correct, follow the replacement direction in the applicable FANUC manual.

4. Replace the Spindle Amplifier if Alarm 19 Remains

For αi SPM alarm 19, FANUC B-65285EN/04 instructs technicians to replace the spindle amplifier. The βiSVSP procedure similarly requires replacement of the βiSVSP when its control board is mounted correctly and the alarm remains.

Before installing a replacement, verify:

• The complete FANUC part number and every suffix

• The amplifier family and hardware specification

• Rated input, output capacity, and supported spindle motor configuration

• Control-board and connector specifications

• Compatibility with the CNC, spindle software, and machine configuration

Do not select a replacement only by cabinet size, output rating, connector appearance, or a shortened model number. FANUC amplifier suffixes and hardware revisions can affect compatibility.

Where model-specific documentation permits board-level service, a qualified repair facility may test the control board, power section, connectors, and U-phase current-detection circuit. However, FANUC's field troubleshooting direction for a confirmed alarm 19 remains replacement of the applicable spindle amplifier unit when board installation is correct.

If a replacement or professional test is required, browse FANUC servo, spindle, and power drives or send REACO CNC the complete amplifier model and suffix for confirmation.

SP9019 Is Not the Same as SP9012 Overcurrent

SP9019 and SP9012 both refer to current-related circuitry, but they identify different conditions:

Do not use SP9012 troubleshooting steps merely because SP9019 contains the word “current.” Motor insulation tests and power-lead checks may be required when a separate alarm or measurement points to them, but they are not FANUC's stated first-line procedure for alarm 19.

Difference Between SP9019 and SP9020

SP9019 and SP9020 are companion offset alarms:

These alarms do not identify the same phase. Always record the actual display rather than referring to both as a general current-offset fault.

FANUC SP9019 Diagnostic Table

Recommended Troubleshooting Order

1. Confirm the CNC alarm and alarm 19 on the spindle amplifier display.

2. Record the complete CNC, spindle amplifier, control-board, and software identification.

3. Confirm that the alarm occurs during power-on initialization.

4. Determine whether the control board or amplifier was recently removed, replaced, repaired, transported, or reinstalled.

5. Isolate power and wait for DC-link discharge according to the applicable safety procedure.

6. For the applicable amplifier series, check that the control board and its connectors are correctly installed.

7. Correct improper board seating or connector plugging and retest at power-on.

8. If alarm 19 remains with the board and connectors correctly installed, replace the spindle amplifier with an exact compatible unit.

9. After replacement, verify that alarm 19 no longer appears and complete the machine builder's spindle test.

10. If a different alarm appears, diagnose the new number separately.

Do not begin by changing spindle parameters, editing the PMC ladder, replacing the spindle motor, or altering current-related adjustments. FANUC does not list these as the standard remedy for alarm 19.

Technical References

• FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Alarm Codes 19 and 20

• FANUC AC Servo Motor βi Series, AC Spindle Motor βi Series, Servo Amplifier βi Series Maintenance Manual, B-65325 series, Alarm Codes 19 and 20

• FANUC AC Servo Motor βi-B/βi Series, AC Spindle Motor βi Series, Servo Amplifier βi-B Series Maintenance Manual, B-65425 series, spindle alarm mapping and maintenance precautions

Always use the manual edition that applies to the exact CNC, spindle amplifier family, control board, spindle software, and machine configuration.

Need Help With FANUC SP9019 Alarm?

REACO CNC provides independent FANUC spindle amplifier testing, repair, compatibility checking, and replacement support. Send us the CNC alarm screen, amplifier display, complete CNC model, exact spindle amplifier model and suffix, control-board number when available, and details of any recent amplifier work.

Visit the FANUC Technical Support Center for more FANUC alarm guides, or contact REACO CNC for assistance.

Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The applicable board inspection and replacement procedure depends on the exact CNC, spindle amplifier series, control board, software, and machine configuration.