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Check the spindle amplifier 3 LED display for the specific alarm code (e.g., AL-11, AL-20, AL-30, AL-50, etc.). Record this code as it identifies the exact fault condition.

Navigate to DIAGNOSIS > SPINDLE screen and check spindle 3 load current and DC bus voltage (typically displays instantaneous values). Compare against normal operating range (load should be <100% rated, DC bus typically 280-320VDC for 200V class).

Verify cooling fans on spindle amplifier 3 are operational and air intake/exhaust vents are clear. Check heatsink temperature if accessible. Most α-series amplifiers have thermal protection triggering AL-20 or AL-21.

Allow amplifier to cool 15-20 minutes before reset if overheating suspected

Check spindle motor 3 power cable routing for damage, pinching, or contamination. Verify U/V/W connections at both amplifier and motor are tight and free of carbon tracking. Measure insulation resistance motor-to-ground (>10MΩ expected when disconnected).

Disconnect amplifier power and wait 5 minutes for DC bus discharge before checking connections

Check amplifier LED for encoder-related codes: AL-40 (serial encoder error), AL-41 (encoder checksum), AL-90 (position error excess), AL-96 (encoder battery low). Navigate to DIAGNOSIS > PARAMETER > SPI and verify spindle 3 encoder type matches parameter 4020#0-3.

Inspect spindle 3 encoder cable (typically separate or combined in motor power cable) for damage, loose connectors at amplifier (CNA or CSP) and motor encoder housing. Check for oil/coolant contamination at motor encoder end.

If encoder is serial type (α-encoder, β-encoder), check DIAGNOSIS > ENCODER screen for spindle 3 position data updating. If zero or frozen, power-cycle the system and observe if encoder initializes (amplifier should show brief AL-94 then clear).

For persistent encoder errors, verify encoder power supply at amplifier connector (typically +5VDC for serial encoders). Check parameter 4025 (spindle encoder serial data) and 4020 (spindle specification) for correct configuration matching motor nameplate.

Incorrect encoder parameters can cause immediate amplifier faults; verify before modification

Check amplifier LED for AL-60 (control PCB), AL-70/AL-71 (power module), or AL-86 (communication error). Verify optical fiber or serial connection between CNC control and spindle amplifier 3 connector (JD1A/JD1B for fiber, typically at back of amplifier).

Navigate to MAINTENANCE > I/O > AXIS CONTROL and check spindle 3 amplifier ready signal status. If not present, check incoming three-phase power to amplifier (R/S/T terminals) for voltage balance (should be within 2% of nominal 200VAC or 400VAC class).

Verify main disconnect is locked-out before measuring high voltage

Check parameter 4020 (spindle motor code) and 4022 (amplifier type) match the installed hardware for spindle 3. Mismatch can cause immediate communication faults. Verify parameter 4023#2 (spindle amplifier assignment) correctly designates third spindle.