FANUC SP9069 Alarm 69: Safety Speed Exceeded and Troubleshooting

FANUC SP9069 means that the spindle motor exceeded the permitted safety speed while Dual Check Safety speed monitoring was active, or that the applicable control detected an abnormal condition during the resulting free-run stop. The CNC displays SP9069 or SSPA:69 SAFETY SPEED OVER, and the spindle amplifier displays alarm 69.

This is a safety-monitoring alarm, not a general indication that the spindle exceeded its normal maximum speed. The official troubleshooting direction is to check the commanded speed, the applicable safety-speed settings, and the machine sequence. On older FANUC systems, the alarm is described specifically in connection with safety signal mode C, when a guard-open request has been entered. If those checks are correct and the alarm remains, the applicable FANUC maintenance manual may direct replacement of the spindle amplifier control printed-circuit board or spindle amplifier.

For adjacent spindle alarms, see the FANUC Spindle Alarm Codes SP9034–SP9092 guide.

What Does FANUC SP9069 Mean?

SP9069 is generated by the spindle side of the FANUC Dual Check Safety system. When safety monitoring is requested, the CNC and spindle amplifier independently supervise spindle motor speed against the active safety-speed setting. If the monitored speed exceeds that setting, the safety monitoring result becomes unsafe and alarm 69 can be issued.

FANUC manuals describe the detection condition in two closely related ways, depending on the CNC generation and manual:

• Older αi maintenance documentation states that alarm 69 can be issued only when Dual Check Safety is used. It describes the alarm as occurring in safety signal mode C, after a guard-open request has been entered, when spindle motor speed exceeds the safety speed.

• Later DCS and CNC alarm lists describe the condition more generally: safety-speed monitoring was enabled and the motor exceeded the safety speed, or an error was detected during a free-run stop.

These descriptions are not contradictory. The older wording identifies a specific operating state in which the safety check is active. The newer wording covers the monitored overspeed condition and the stop behavior that follows it. Always use the manual edition for the installed CNC, spindle software, and DCS configuration.

SP9069 does not, by itself, prove that the spindle amplifier, motor, encoder, power cable, or CNC main board has failed. It first proves that the DCS safety-speed logic detected an unsafe result.

How FANUC DCS Spindle Speed Monitoring Works

The Series 30i-A Dual Check Safety manual identifies four selectable safety-speed settings for each spindle:

The active value is selected by the spindle safety-speed selection signals SPAs and SPBs. The safety check request signal is written *VLDPs in FANUC documentation. The asterisk matters: it is an active-low signal, so *VLDPs = 0 requests the spindle safety check. If the speed is outside the selected safe range, the spindle monitoring result signal RSPs changes to the unsafe state and SP9069 can occur.

The safety-speed values are specified in terms of motor speed, not necessarily the tool-side or spindle-nose speed shown by an S command. Gear range, pulley ratio, gearbox ratio, and machine-builder spindle conversion logic therefore matter when comparing the programmed speed with the DCS limit.

Do not assume that No. 4372 is always the active limit. The SPAs/SPBs signal combination determines which of the four values is selected. A correct value in one parameter does not compensate for an incorrect selection signal or an incorrect value in another selected parameter.

Safety Precautions Before Troubleshooting

SP9069 is part of a personnel-protection function. Treat it as a safety event.

• Do not bypass the protective-door circuit, force the guard-unlock output, or disable Dual Check Safety to keep the machine running.

• Do not raise a safety-speed parameter merely to clear the alarm.

• Do not force *VLDPs, SPAs, SPBs, RSPs, or an MCC control signal in the PMC.

• Do not modify a safety parameter or ladder sequence without the machine builder's approved data, a backup, authorized personnel, and the required safety validation afterward.

• Do not open the cabinet or handle power wiring until the machine is isolated and the specified DC-link discharge time has elapsed.

Record the alarm and operating state before cycling power. Repeated resets can erase the sequence evidence needed to distinguish an incorrect command from a signal-timing or stopping problem.

1. Confirm SP9069 and the Exact Trigger Condition

Confirm that the CNC shows SP9069 and the spindle amplifier shows 69. Then identify exactly when it occurs:

Also record:

• CNC series, model, and system software edition

• Complete spindle amplifier model and suffix

• Spindle motor model and feedback-device type

• DCS manual number and machine-builder safety documentation

• Program block, S command, spindle override, and operating mode

• Guard-open request, door state, selected gear range, and active safety-speed selection

• Commanded spindle speed, actual spindle speed, and motor speed if separately available

• Any recent parameter, ladder, motor, amplifier, encoder, gearbox, or wiring work

2. Check the Commanded Speed and Operating Sequence

FANUC's later alarm list places the speed command first. Confirm that the commanded motor speed is below the selected DCS safety limit before the safety check becomes active.

Review all sources that can affect the final motor command:

• Programmed S command

• Manual spindle command and spindle override

• Gear-range or winding-switching state

• Spindle orientation, positioning, or Cs-axis operation

• Rigid tapping, spindle synchronization, electronic gearing, or other coordinated modes

• Machine-builder speed conversions and range-dependent ratios

• Commands retained during a transition to guard-open or setup operation

A spindle S command and a DCS parameter cannot always be compared as equal rpm values. Calculate or observe the resulting motor speed for the active mechanical range. For example, a low tool-side speed can still correspond to a higher motor speed through a transmission ratio.

The guard-opening sequence must reduce the spindle to the permitted range before the protective door is unlocked. If the guard-open request activates safety monitoring while the spindle is still above the selected limit, SP9069 is an expected protective response. Correct the command or sequence; do not increase the limit to conceal the timing error.

3. Verify the Safety-Speed Parameters and Selection

Compare the installed safety data with the machine builder's approved backup. On systems using the cited parameter arrangement, inspect No. 4372, No. 4438, No. 4440, and No. 4442 together with SPAs/SPBs.

Check that:

• Each safety-speed value is correct for the machine, spindle, tooling policy, and corresponding selection state.

• The value is interpreted as motor speed where specified by the applicable FANUC manual.

• The correct value is selected for the current operating mode and guard condition.

• Both safety channels contain and accept the approved data.

• The required power-off/power-on and safety-parameter confirmation procedure was completed after an authorized change.

• The safety data was not copied from another machine with a different motor, pulley, gearbox, or spindle range.

In the Series 30i-A DCS documentation, parameter No. 4448 is the stop check level. During a free-run response, the motor is regarded as stopped after its speed falls below this level, and the alarm can then become resettable. This setting must remain below the applicable safety speed. Check it only against approved machine data; it is not a substitute for correcting a spindle that fails to decelerate normally.

Some later DCS implementations provide a series-specific selection between free-run and controlled stopping after a safety-speed violation. Do not apply a parameter number or stop method from a different CNC generation. Confirm the exact behavior in the DCS manual for the installed control.

4. Check *VLDPs, SPAs/SPBs, RSPs, and the Guard Sequence

The technician's reference to a “VLDPs signal” is directionally useful, but the official signal name is normally *VLDPs, and it is active low. Diagnose the entire safety sequence rather than one bit in isolation.

Observe the relevant signal states in the CNC and PMC diagnostics while reproducing the event under an approved, controlled test procedure:

• ORQ or equivalent guard-open request: identifies the request to enter the guard-open sequence on applicable systems.

• *VLDPs: requests safety checking for the spindle when it becomes 0.

• SPAs/SPBs: select safety speed 1, 2, 3, or 4.

• RSPs: reports whether the spindle is within the selected safe-speed range.

• Guard state and guard-lock feedback: confirm that physical door status agrees with the sequence.

• *MCFPs: participates in the DCS response that removes spindle power through the machine's safety circuit when required.

Look for incorrect order, insufficient delay, mismatched redundant inputs, or a transient selection change. A common sequence problem is requesting the safety check before the spindle has decelerated below the selected limit. Another is changing SPAs/SPBs at the wrong time so that a lower limit becomes active while the motor is still above it.

FANUC documentation requires the machine-tool builder's ladder to coordinate the guard lock and the redundant monitoring results. Any ladder correction must therefore be made and validated by personnel authorized to work on the machine's safety control. A normal PMC edit and a safety-function modification are not equivalent tasks.

5. Investigate an Alarm During Free-Run Stopping

When a safety-speed violation causes the spindle to enter a free-run state, the system expects motor speed to decrease. FANUC DCS documentation explains that if the spindle does not decelerate as required, the safety system proceeds to a safe-stop response. Later alarm lists include an abnormality detected during free-run stop as a possible SP9069 condition.

If the alarm is associated with stopping rather than the initial overspeed, check:

• Whether the speed command and excitation are removed in the intended order

• Whether actual motor speed decreases continuously after the stop response begins

• Whether a mechanical process, driven tool, workpiece, secondary spindle, transmission, or stored energy can back-drive the spindle

• Whether a contactor or power-switching device remains in an unintended state

• Whether the motor-speed feedback is stable and plausible during deceleration

• Whether the approved stop-check level and stop method match the machine design

• Whether the MCC-off sequence and feedback operate as specified

Do not attempt to reset the alarm while the spindle is still rotating above the permitted reset condition. If the spindle accelerates, maintains speed unexpectedly, or continues to receive torque after the safety response, isolate the machine and investigate the control and power circuit before another test.

6. Check Motor Initialization, Feedback, and Power Wiring Only When Evidence Supports It

Motor initialization data and power wiring are reasonable secondary checks when the observed motor speed does not agree with the command, when the alarm began after spindle hardware work, or when the free-run response is abnormal. They are not the first universal remedy for SP9069.

Check the following against the exact FANUC spindle parameter manual and machine-builder data:

• Complete motor model and approved initialization data

• Motor maximum speed, feedback type, pulse data, and speed-conversion settings

• Gear or pulley ratio used by the spindle command and displayed speed

• Motor sensor and feedback cable connections, shielding, and diagnostic speed indication

• U/V/W power-lead connections and phase order if they were recently disturbed

• Spindle contactors, winding-switching hardware, and power-circuit feedback states

• Input power and common power-supply status if another alarm or measurement indicates a supply problem

An initialization error or incorrect feedback scaling can make the monitored motor speed inconsistent with the intended machine speed. Incorrect power wiring or a stuck switching device can also matter when there is evidence of unintended torque or abnormal stopping. However, replacing cables or changing phase order without evidence can introduce a second fault and does not address an ordinary command, safety-parameter, or sequence error.

7. Consider the Spindle Amplifier After External Causes Are Excluded

For the older αi alarm 69 procedure, FANUC instructs technicians to observe the safety speed, check the safety-speed parameter, and then replace the spindle amplifier control printed-circuit board if the condition remains. Other generations may specify replacement of the spindle amplifier rather than field replacement of its control board.

Before replacement, confirm that:

• The speed command is correct.

• The active safety-speed limit and selection signals are correct.

• The guard and safety-check sequence is correct.

• The spindle decelerates as the applicable stop method requires.

• Motor initialization and actual-speed feedback are credible.

• No other CNC, DCS, spindle, feedback, or power alarm identifies a separate fault.

Select replacement hardware by the complete FANUC part number, series, suffix, software support, and DCS compatibility. Do not choose a replacement only by appearance or output rating. If required, browse FANUC servo, spindle, and power drives or send the complete model to REACO CNC for a compatibility check.

8. Retest and Validate the Safety Function

After correcting the cause, perform the machine builder's commissioning and DCS validation procedure. Confirm all of the following:

• The intended one of the four safety-speed values is selected in every relevant operating mode.

• Actual motor speed remains below the selected limit before and while *VLDPs requests monitoring.

• RSPs and the redundant safety-channel results change as designed.

• The guard remains locked until the spindle is within the permitted state.

• The configured stop response and MCC-off path operate correctly.

• SP9069 and amplifier alarm 69 do not recur during approved tests.

• All required safety-parameter signatures, checksums, test records, and acceptance results are complete.

Clearing the alarm is not sufficient proof that the safety function is correct. Any change to safety parameters, safety I/O, ladder logic, amplifier hardware, feedback hardware, or the stopping circuit requires the validation specified by FANUC and the machine builder.

Difference Between SP9050, SP9069, and SP9072

Use the exact alarm number shown on both the CNC and spindle amplifier. Do not diagnose every speed-related spindle alarm as SP9069.

FANUC SP9069 Diagnostic Table

What Not to Do With SP9069

• Do not disable DCS for the affected spindle to make production continue.

• Do not increase No. 4372, No. 4438, No. 4440, or No. 4442 without the machine's safety-risk assessment and approved data.

• Do not force *VLDPs, SPAs, SPBs, RSPs, guard-lock, or MCC signals.

• Do not assume the S command equals motor rpm without accounting for the active range and ratio.

• Do not replace the spindle amplifier before checking the command, safety data, and signal sequence.

• Do not copy parameters or ladder logic from another machine merely because it uses a similar FANUC control.

• Do not return the machine to service without the required DCS functional test and documented validation.

Recommended Troubleshooting Order

1. Confirm SP9069 on the CNC and 69 on the spindle amplifier.

2. Record the program block, actual speed, guard state, gear range, selected safety speed, and signal chronology.

3. Determine whether the alarm occurred during monitored operation or during the free-run stop response.

4. Verify that the commanded motor speed is below the selected safety limit.

5. Compare parameters No. 4372, No. 4438, No. 4440, and No. 4442 with the approved machine backup where those numbers apply.

6. Confirm the SPAs/SPBs selection and active-low *VLDPs timing.

7. Check RSPs, guard-state, guard-lock, and MCC-related sequence behavior.

8. If the event occurred during stopping, verify continuous deceleration, stop-check conditions, and the power-removal path.

9. Only when the evidence supports it, verify motor initialization, feedback scaling, sensor wiring, power leads, and contactor states.

10. If all commands, parameters, signals, and external hardware are correct, follow the applicable FANUC instruction for control-board or spindle-amplifier replacement.

11. Complete the required DCS commissioning and safety validation before returning the machine to service.

Technical References

• FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Alarm Code 69

• FANUC Series 30i-A Dual Check Safety Operator's Manual, B-64004EN/02, Safety Check Request Signal, Safety Speed Parameters, and SP9069

• FANUC Series 0i-D Dual Check Safety Connection Manual, B-64303EN-4/01, SP9069 Alarm List

• FANUC Series 30i-B/31i-B/32i-B Dual Check Safety Connection Manual, B-64483EN-2 series, Safe Speed Monitoring

• FANUC Series 500i-A Maintenance Manual, B-64805EN/03, SP9069 Alarm List

Use the manual edition that applies to the exact CNC, spindle amplifier, spindle software, DCS option, machine-builder safety circuit, and machine configuration.

Need Help With FANUC SP9069 Alarm?

REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC spindle amplifiers, control boards, CNC hardware, and related drive components. Send us the CNC alarm screen, spindle amplifier display, complete CNC model, exact spindle amplifier model and suffix, motor model, DCS configuration, active safety-speed selection, and a description of when the alarm occurs.

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

Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The applicable parameters, signals, stop behavior, replacement procedure, and safety validation depend on the exact CNC, spindle amplifier, software, DCS configuration, and machine.