FANUC SP9086 means that the spindle amplifier did not detect the required one-rotation signal from the spindle sensor. The CNC displays SP9086, while the spindle amplifier displays alarm 86.
FANUC Maintenance Manual B-65285EN/04 states that no spindle-sensor one-rotation signal occurred and instructs technicians to troubleshoot alarm 86 by referring to the alarm-82 procedure. Alarm 82 covers a missing motor-sensor one-rotation signal; for SP9086, the same diagnostic logic must be applied to the actual spindle-sensor circuit.
| Alarm item | Display or condition | Meaning |
|---|---|---|
| CNC alarm | SP9086 | Required spindle-sensor one-rotation signal was not detected |
| Spindle amplifier | 86 | No valid once-per-revolution reference reached the amplifier |
| FANUC cross-reference | Troubleshoot as alarm 82 | Check the applicable parameters, sensor, signal cable or external reference, and amplifier |
| Possible spindle-side input | PS2 through JYA4 on certain documented configurations | Confirm the amplifier type and wiring before testing |
| External reference example | EXTSC1 through JYA3 on a documented αi-B arrangement | Do not assume an external proximity switch uses JYA4 |
For the surrounding serial spindle alarms, see the FANUC Spindle Alarm Codes SP9034–SP9092.
What Is the Spindle-Sensor One-Rotation Signal?
A spindle detector can provide repeating phase A/B feedback plus a reference that occurs once per spindle revolution. FANUC manuals refer to the reference as the one-rotation signal. Depending on the detector, it may also be described as a phase-Z, index, marker, or once-per-revolution signal.
“No signal” can mean more than a completely failed sensor. Possible causes include:
- Incorrect detector or spindle-sensor parameters
- Selection of the wrong feedback source
- An incorrectly adjusted spindle sensor
- Excessive or nonuniform clearance between the sensor head and detection ring
- A damaged, contaminated, or stationary detection ring
- A broken or incorrectly connected feedback cable
- Loose, corroded, or contaminated connector contacts
- A defective external one-rotation proximity switch or its cable
- Poor frame grounding or feedback-cable shielding
- Feedback wiring routed beside motor power leads
- An unsuitable replacement cable specification
- A failed spindle-amplifier input circuit
The correct test depends on whether the machine uses a spindle-side sensor, position coder, serial detector, or external one-rotation switch.
Difference Between SP9085 and SP9086
| CNC alarm | Amplifier display | One-rotation signal condition | Main diagnostic question |
|---|---|---|---|
| SP9085 | 85 | Signal occurs at an incorrect position | Why is the reference position inconsistent? |
| SP9086 | 86 | Signal is not generated or detected | Where is the reference signal lost? |
SP9085 can involve an incorrect mechanical relationship, gear ratio, or shifted detector position. SP9086 begins with signal existence: confirm whether the reference is generated by the sensor and whether it reaches the correct spindle-amplifier input.
Do not treat the two alarms as interchangeable.
Does SP9086 Always Use Connector JYA4?
No. JYA4 is used as a spindle-side or second-sensor input on certain FANUC configurations, but the alarm number alone does not establish the connector.
For a documented αi-B spindle-side sensor configuration, the maintenance manual identifies:
| Check signal | Documented connector assignment | Function |
|---|---|---|
| PA2 | JYA4 pins 5 and 6 | Spindle-sensor phase A |
| PB2 | JYA4 pins 7 and 8 | Spindle-sensor phase B |
| PS2 | JYA4 pins 1 and 2 | Spindle-sensor one-rotation signal |
The same manual identifies EXTSC1 at JYA3 pin 15 for an external proximity-switch one-rotation signal. Therefore, a machine using an external reference may require inspection of JYA3 and the external switch rather than JYA4.
Connector use varies by amplifier family, hardware specification, detector type, and option. Confirm the full spindle-amplifier model, machine wiring diagram, and applicable connection manual before disconnecting or probing any feedback connector.
1. Confirm the Exact Alarm and Feedback Configuration
Before replacing a cable or sensor, confirm:
- The CNC screen shows SP9086.
- The spindle amplifier display shows 86.
- The machine uses a separate spindle sensor or an external one-rotation signal.
- The detector type, signal source, and connector match the machine drawing.
- The alarm occurs immediately, only after a rotation command, during orientation, or at a specific operating state.
- The problem started after parameter loss, spindle work, detector adjustment, amplifier replacement, or cable service.
- Other sensor or spindle alarms are present.
Record the CNC series, amplifier model and suffix, spindle motor, spindle-sensor type, spindle software, detector parameters, connector positions, and alarm timing.
If the spindle never turns, first determine whether alarm 86 is the primary fault or a consequence of another condition that prevents rotation.
2. Back Up and Verify the Detector Parameters
The first general item in FANUC's alarm-82 procedure is an incorrect parameter setting. Compare the machine with the applicable FANUC AC Spindle Motor Parameter Manual B-65280EN and the machine builder's original parameter list.
Verify as applicable:
- Spindle-sensor or detector type
- Selection of the spindle-side feedback channel
- Number of detector teeth or pulses
- Use of an external one-rotation signal
- Rotation direction
- Position-feedback selection
- Motor-to-spindle relationship
- Machine-specific spindle-position options
Do not initialize the entire spindle parameter set as a shortcut. Full initialization can erase motor, detector, orientation, gear, and machine-specific settings. Save a verified backup and correct only values supported by the exact documentation. If the machine builder specifies a controlled reinitialization procedure, follow it and restore the correct data afterward.
A parameter error is especially likely after memory loss, parameter restoration from another machine, control-board replacement, spindle-amplifier replacement, or a detector conversion.
3. Determine Which One-Rotation Signal Is Missing
The most efficient diagnosis identifies whether the machine uses an internal spindle detector or an external one-rotation input.
Spindle-Side Sensor or Position Detector
On a documented JYA4 arrangement, compare the A/B feedback at PA2/PB2 with the one-rotation signal at PS2. This comparison helps isolate the fault:
- A/B feedback present but PS2 absent: focus on the one-rotation element, phase-Z portion of the detector, detection ring, sensor adjustment, or PS2 conductor.
- A/B feedback and PS2 both absent: check detector power, connector engagement, common cable failure, parameter selection, sensor failure, and amplifier input.
- Signal present at the detector but absent at the amplifier: inspect the cable, connector, pin assignment, shield termination, and intermediate connections.
Use only the test board, check terminals, measuring equipment, rotation direction, and waveform limits specified for the installed hardware.
External One-Rotation Proximity Switch
FANUC's alarm-82 procedure instructs technicians to check the external one-rotation signal when that function is used. In the αi-B example, the check point is EXTSC1. If the signal is not generated once per revolution, inspect the proximity switch, target, mounting, sensing distance, connection cable, and applicable position detector.
Do not replace a JYA4 spindle-feedback cable when the machine's missing reference actually comes through an external-switch circuit.
4. Inspect and Adjust the Spindle Sensor
FANUC directs technicians to adjust the sensor and replace the connection cable and sensor if adjustment is impossible or the signal cannot be observed. Apply this step to the actual spindle-side detector used by the machine.
Depending on the configuration, the detector may be an αiBZ sensor, an αiCZ sensor, a position coder, or another supported device. Check:
- Sensor-head mounting and security
- Sensor-to-ring clearance
- Uniform gap around a full spindle revolution
- Detection-ring concentricity and runout
- Damage, wear, impact marks, or metal debris
- Correct phase A/B and one-rotation waveforms
- Evidence that the ring or target is not rotating
- Correct sensor and ring combination
When adjusting an αiBZ sensor, FANUC warns that the sensor head must not contact the detection ring. A collision can damage the detector. Use the specified gauge and detector-specific method.
The illustration translates the supplied field reference. It shows an integrated A/B-phase and Z-phase ring, heat-fit installation, and a 0.15 mm example clearance. The 0.15 mm value is not universal. Confirm the required gap, ring design, installation method, and allowable runout for the exact detector and machine.
5. Inspect the Feedback Cable and Connectors
With machine power isolated and the specified discharge time observed, inspect the complete signal path:
- Connector engagement and locking hardware
- Bent, recessed, corroded, or contaminated contacts
- Cable damage near the spindle, clamps, cabinet entry, and cable carrier
- Internal conductor fatigue at repeatedly flexed sections
- Oil or coolant inside the connector or cable jacket
- Poor strain relief or excessive bend radius
- Nonstandard splices, extensions, or substituted cables
- Correct continuity and pin-to-pin assignment
- Correct connection of the one-rotation pair
If JYA4 is documented for the spindle-side sensor, verify the PS2 circuit as well as the A/B pairs. If an external switch is used, inspect that separate signal cable and connector path.
Replace a cable that is open, intermittent, incorrectly pinned, contaminated beyond service, or outside the required specification.
6. Verify Grounding, Shielding, and Cable Routing
The αi-B alarm-82 procedure expands the checks to include frame grounding, shielding, cable routing, and cable construction. These items are especially relevant when the signal disappears only at certain speeds or when adjacent power equipment operates.
Verify that:
- The spindle, detector housing, and amplifier cabinet use the documented low-impedance ground.
- Ground conductors contact clean, unpainted surfaces where specified.
- Signal-ground and power-ground installation follows the FANUC and machine documentation.
- The feedback shield remains continuous through connectors and relay sections.
- Shield clamps provide secure low-impedance contact.
- Unshielded conductor lengths are kept short.
- Sensor and thermistor conductors use the specified twisted-pair arrangement.
- The feedback cable is not bundled with spindle or servo motor power leads.
FANUC instructs technicians to separate feedback wiring from motor power wiring when it is bundled or routed in parallel. Use the correct shielded cable rather than a physically compatible but electrically unsuitable substitute.
7. Treat Belt and Detection-Ring Checks as Configuration-Specific
The field procedure supplied for this article recommends checking the spindle-sensor belt and the security of the detector. That is reasonable when a belt, gear, or coupling physically drives the reference target. If the target does not rotate, the amplifier cannot receive a once-per-revolution signal.
Inspect as applicable:
- Broken or missing timing-belt teeth
- A belt that is completely loose or no longer driving the sensor
- Loose pulleys, gears, keys, or couplings
- A detection ring that has shifted or stopped rotating with the spindle
- Sensor brackets that moved after maintenance or impact
Ordinary slippage that changes the angular relationship but still produces a signal more directly matches SP9085. For SP9086, use this mechanical branch when there is evidence that the sensor target is not passing the detector or that the one-rotation element is not being actuated.
8. Replace the Spindle Amplifier Only After External Checks
If the correct parameters, signal source, sensor adjustment, external switch, cable, connectors, grounding, shielding, routing, and mechanical drive have been verified, the spindle-amplifier input circuit may be defective.
For hardware covered by B-65285EN/04, the referenced alarm-82 procedure permits replacement of the spindle amplifier or spindle-amplifier control printed-circuit board. Other series can specify the control board or complete amplifier. Follow the service level for the installed hardware.
Before selecting replacement hardware, verify the complete FANUC part number and suffixes, amplifier series, hardware revision, supported detector channel, spindle software compatibility, connector layout, and commissioning requirements.
If replacement hardware is required, browse FANUC servo, spindle, and power drives or send the complete model and suffix to REACO CNC for a compatibility check.
FANUC SP9086 Diagnostic Table
| Finding | Interpretation | Recommended action |
|---|---|---|
| CNC shows SP9086 and amplifier shows 86 | Spindle one-rotation signal is not detected | Identify the actual signal source and apply the alarm-82 procedure to that channel |
| Amplifier shows 85 | The signal exists but occurs at an incorrect position | Use the SP9085 procedure instead |
| A/B signals are present but PS2 is absent | The one-rotation element or its conductor may be faulty | Check phase-Z signal, ring, adjustment, PS2 wiring, sensor, and amplifier input |
| No spindle-sensor signals are present | Common sensor power, parameters, cable, connector, or detector may be faulty | Verify selection, power, cable, connector, and sensor output |
| External switch is configured | The reference may enter through a separate input such as EXTSC1 | Test the switch, target, distance, cable, and documented input |
| Alarm began after parameter loss | Detector or feedback-source selection may be wrong | Compare the backup with the correct parameter manual |
| Gap changes through one revolution | Ring runout or sensor mounting is incorrect | Correct the mechanical cause to the specified tolerance |
| Alarm changes when the cable moves | A conductor or connector may be intermittent | Inspect flex sections and replace the defective cable |
| Alarm occurs only during powered motion | Noise may be masking the signal | Check grounding, shielding, cable construction, and power-cable separation |
| All external checks pass | Spindle-amplifier input hardware may be faulty | Replace the supported control board or complete amplifier |
What Not to Do With Alarm 86
- Do not confuse SP9086 with the incorrect-position alarm SP9085.
- Do not assume every alarm-86 machine uses JYA4.
- Do not overlook an external one-rotation switch and its separate input.
- Do not initialize all spindle parameters without a verified backup and exact procedure.
- Do not call every spindle detector an encoder or apply one adjustment method to all types.
- Do not apply a 0.15 mm gap to every αiBZ, αiCZ, or position-detector installation.
- Do not replace a cable without verifying the connector and pin assignment.
- Do not bundle the sensor cable with motor power leads.
- Do not replace the spindle amplifier before the external signal path is checked.
Recommended Troubleshooting Order
- Confirm SP9086 on the CNC and alarm 86 on the spindle amplifier.
- Record the alarm timing, complete amplifier model, detector type, parameters, connector, and machine configuration.
- Determine whether the machine uses a spindle-side sensor or an external one-rotation switch.
- Back up and verify the detector and feedback-source parameters against the applicable documentation.
- Check whether A/B feedback exists and whether the one-rotation signal is missing at PS2 or the documented equivalent.
- For an external reference, check EXTSC1 or the correct input, proximity switch, target, sensing distance, and cable.
- Inspect and adjust the spindle sensor, detection ring, clearance, mounting, and runout.
- Inspect the complete feedback cable and connectors, including JYA4 only where documented.
- Verify grounding, shield continuity, cable construction, and separation from power wiring.
- Check belts, gears, couplings, and ring rotation only where they drive the detector or target.
- Replace the correct cable and sensor if the one-rotation signal cannot be observed.
- Replace the supported spindle-amplifier control board or complete amplifier only after external causes are eliminated.
- Retest spindle rotation, orientation, positioning, and affected machine functions under the machine-builder procedure.
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 82 and 86
- FANUC AC Servo Motor αi-B Series, AC Spindle Motor αi-B Series, Servo Amplifier αi-B Series Maintenance Manual, B-65515EN/01, Alarm Code 82 and spindle-sensor check terminals
- FANUC AC Servo Motor βi Series, AC Spindle Motor βi Series, Servo Amplifier βiSVSP Maintenance Manual, B-65325EN/02, Alarm Codes 82 and 86
- FANUC AC Spindle Motor αi/βi Series Parameter Manual, B-65280EN, detector and spindle-sensor settings
- FANUC Servo Amplifier αi-B Series Descriptions, B-65412EN, detector connections, grounding, shielding, and cable routing
Always use the manual edition that applies to the exact CNC, spindle amplifier, spindle software, sensor, connector arrangement, and machine.
Need Help With FANUC SP9086 Alarm?
REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC spindle amplifiers, spindle sensors, feedback cables, control boards, and related hardware. Send us the CNC alarm screen, amplifier display, complete CNC and amplifier models, spindle-sensor type, parameter backup, connector photos, sensor installation photos, and details of when SP9086 occurs.
Visit the FANUC Technical Support Center for more FANUC alarm guides, or contact REACO CNC for assistance.
Reference Source: FANUC technical documentation. The correct procedure depends on the detector type, selected signal source, parameters, cable installation, amplifier, and machine-builder design.
