The Fanuc Alpha i spindle amplifier module — the SPM in everyday field talk — is the power stage driving the AC spindle motor on machining and turning centres running 0i, 16i/18i, 21i and 30i/31i controls. It comes in order-code families A06B-6111-H0xx (SPM-2.2i to SPM-37i), A06B-6112-H0xx and A06B-6141-Hxxx, and sits downstream of the PSM on the same DC link. Because it switches spindle current, it carries the widest alarm range of any drive module — and knowing which codes point at the machine rather than the amplifier is what turns a two-visit fault into a one-visit fix.
Please check our Fanuc drive modules collection for the PSM, SPM and related part numbers we stock.
The STATUS display has a PIL LED (green = normal), an ALM LED (red = alarm) and a two-digit 7-segment readout showing codes 01–88 plus A, A1, A2, b0, C0, C1 and C2. The CNC shows a matching SP alarm whose number follows the LED code: 01→SP9001, 12→SP9012, 31→SP9031, 73→SP9073.
Manifestations. Trips after minutes of cutting, or under light load. Motor housing hot, cooling fan silent.
Root causes. Fanuc documents three branches. During cutting: stopped or blocked motor fan, clogged finger guard, ambient above specification, duty cycle beyond the short-period rating. Under light load: acceleration/deceleration frequency pushing average output past the continuous rating, or motor parameters not matching the fitted motor. Motor actually cool: faulty feedback cable, failed SPM control PCB, or a dead motor thermostat.
Repair steps. Lock out and wait for the CHARGE LED to go out. Measure fan current against nameplate, clean the finger guard and ventilation port, and confirm ambient is inside the 0–55 °C window with bearing temperature below 80 °C. If the motor is genuinely cool, ring out the thermostat circuit and check the connector for coolant ingress. Verify motor parameters against the AC Spindle Motor i series Parameter Manual (B-65280EN) before exchanging hardware.
Manifestations. The spindle runs but hunts, reaches set speed slowly, or stalls as the tool enters the cut with the load meter near its limit.
Root causes. Mechanical overload, belt slip or a loose pulley, a dragging spindle bearing, a faulty speed sensor or feedback cable, or a faulty SPM.
Repair steps. With power off, confirm the spindle turns freely by hand. Check belt tension and pulley condition. Inspect sensor adjustment and cable shielding. Replace sensor and cable first — an A860-2000-X021 speed encoder costs a fraction of an SPM and fails far more often. Exchange the SPM only once the feedback path is proven.
Manifestations. Appears after a period of normal running, worse in summer or with dirty cabinet filters, and clears once the machine cools.
Root causes. Internal or external SPM fan stopped, conductive dust clogging the heat-sink fins, a blocked cabinet filter, or ambient above specification.
Repair steps. Power down for at least five minutes, then vacuum and blow out the fins with dry low-pressure air. Confirm both fans rotate freely with supply present — a fan that runs but moves no air brings the alarm back within weeks. Clean or replace cabinet filters.
Manifestations. AL-11 usually appears during deceleration, on emergency stop or at power-on, often alongside a PSM alarm. AL-12 stops the machine violently, sometimes with a blown DC-link fuse (AL-03).
Root causes. AL-11: faulty incoming supply or PSM, regenerative energy from a high-inertia spindle, or an incorrect input voltage tap. AL-12: a short or ground fault in the motor windings, a damaged power cable, or a failed SPM power stage.
Repair steps. For AL-11, measure all three phases for unbalance or a missing phase, read the PSM display, and lengthen the deceleration ramp — it almost never means a failed SPM. For AL-12, disconnect the motor at the SPM and megger the windings and cable to ground before ordering anything. Fitting a new SPM onto a grounded motor destroys the new module too.
Manifestations. The spindle is commanded but does not turn, or turns far below command, with the alarm issued almost immediately.
Root causes. A mechanical lock — seized bearing, jammed gear or collet, brake not releasing; a faulty speed sensor or feedback cable; or a faulty SPM.
Repair steps. With power off, confirm the spindle rotates freely and the brake releases. Then verify sensor signal and cable continuity. Exchange the SPM only when the spindle is mechanically free and the feedback path is proven.
Manifestations. AL-56 reports the control-circuit cooling fan stopped; AL-88 reports the heat-sink fan stopped. Both appear at power-up and are hard stops.
Root causes. Worn or seized fan bearings, a fan lead broken by vibration, or a fan with no supply.
Repair steps. Spin each fan by hand — it should feel light and even; a gritty fan is finished. Measure supply at the connector. Fit the correct fan for the module rating, confirmed against its parts list: an A06B-6111-H037, for example, uses internal fan A90L-0001-0511 and external fan A90L-0001-0509. Never jumper a fan to finish a shift — AL-09 and a wrecked power stage follow.
Manifestations. AL-73 means the motor sensor signal is disconnected, AL-84 the same for the spindle sensor. Expect the alarm at power-up with the motor stationary, intermittently as the spindle moves, or continuously during rotation.
Root causes. Motor de-energised: sensor-type parameter does not match the sensor fitted, cable disconnected, MZi/BZi sensor misadjusted, or faulty SPM. Cable moved: a broken conductor or coolant inside the connector. Motor rotating: faulty shielding, or the sensor cable bundled with the motor power lead.
Repair steps. Check the sensor parameter against B-65280EN, then cable continuity, then clean and re-adjust the sensor. If the signal cannot be brought into specification, replace cable and sensor together — on the motor side that usually means the A860-2001-T321 spindle encoder. Separate sensor cable from motor power lead and ground the shield at one end only.
Codes A, A1, A2, 13, 16, 18, 19, 20, 32, 74 and 75 are internal CPU, memory, ROM or current-detection failures. The documented action for all of them is to replace the SPM or its control PCB — cleaning will not help. Codes 01, 02, 09, 11, 31, 56, 73, 84 and 88 are usually machine or supply faults, and the amplifier is the last item to change.
When ordering, quote the full model code (for example A06B-6111-H030) with its suffix such as #H550, and the rating from SPM-2.2i to SPM-37i. Control-PCB and software versions must match your control generation.
| Interval | Task | Acceptance criterion |
|---|---|---|
| Daily | Spindle noise, vibration, load meter, amplifier and cabinet fans | Load within continuous rating |
| Monthly / 500 h | Clean SPM heat sink and motor fan finger guard; measure fan current | Fan current within nameplate tolerance |
| Every 3 months | Clean the spindle motor cooling fan; measure fan insulation resistance | Fan turns freely; insulation above 100 MΩ |
| 6 months | Bearing temperature and vibration; clean ventilation ports | Bearing below 80 °C; no abnormal vibration |
| Annually | Replace cabinet filters; torque-check contactors; back up parameters | Parameters archived off-machine |
Keep a spare A860-2020-T341 industrial encoder plus a pair of drive cooling fans on the shelf, and log the absolute pulsecoder battery replacement date rather than waiting for the APC alarm. These are the parts that cause most unplanned spindle downtime, at a fraction of an SPM's cost.
My SPM shows 24. Is the drive faulty? No, provided the CNC control is off — AL-24 is a normal serial-transfer state then.
LED 0 and green PIL, but the spindle will not turn. Now what? The amplifier is ready, so the fault is upstream: emergency-stop chain, door interlock, spindle enable, PMC ladder.
Is it the SPM or the PSM? Read the PSM's STATUS display first. Alarms 04, 05, 08, 10, 11, 30, 33, 51, 58 and 59 are power-supply related, and a PSM fault triggers the SPM alarm as a secondary effect.
Must I re-initialise anything after fitting a replacement SPM? Yes — set the spindle parameters to match the motor, confirm sensor adjustment, and on C-axis contouring machines re-check the position coder one-rotation signal.
Fanuc, Alpha i and SPM are trademarks of Fanuc Corporation.
