Spindle won't start, VFD shows alarm, or motor hums but doesn't rotate — this guide covers all water-cooled and air-cooled CNC spindle startup faults for UAE machine operators.
Overcurrent, overvoltage, or overload fault on the variable frequency drive
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Signal Wiring Issue
Missing 0–10V signal from controller to VFD AVI input terminal
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Wrong VFD Parameters
Operation mode, frequency source, or max frequency set incorrectly
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Cooling Pump Failure
Water-cooled spindle: pump not circulating coolant → thermal protection trips
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Motor Wiring Fault
Loose U/V/W phase wiring between VFD and spindle motor
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Spindle Motor Failure
Burned windings or seized bearings — motor physically failed
Step-by-Step Fix Guide
Follow in order — most faults are resolved by Step 3
1
Check VFD (Inverter) Display & Alarm Codes
The Variable Frequency Drive controls spindle motor speed. Check the VFD display for error codes (F001, OC, OV, OL are common). If the VFD shows an alarm, note the code — it tells you exactly what failed.
Take a photo of the VFD alarm code and send it to WhatsApp +971 56 798 6740. Our team can tell you the exact cause within minutes.
2
Verify Spindle Enable Signal from Controller
The CNC controller sends a 0–10V analog signal to the VFD to command spindle start. Check the wiring from controller output to VFD input terminals (AVI/ACM on most drives). A loose wire here prevents startup.
Use a multimeter on the AVI terminal while commanding spindle ON in the controller. You should see 0–10V proportional to the commanded speed. Zero volts means the controller is not sending the signal.
3
Check VFD Parameter Settings
Verify VFD parameters: operation mode (should be external terminal control, not panel control), frequency source, and max frequency (typically 400Hz for CNC spindles). Wrong parameters = spindle appears to start but doesn't reach speed.
Common VFD error after reset: Pd013 (operation source) accidentally set to keypad (0) instead of external terminal (1). This makes the spindle only respond to the VFD panel, not the CNC controller.
4
Inspect Spindle Motor Wiring
Check the 3-phase wiring between VFD output (U, V, W terminals) and spindle motor. Look for loose terminals, burned insulation, or broken wires. A missing phase causes the spindle to hum but not rotate.
With power OFF, use a multimeter in continuity mode to verify all 3 phases have continuity from VFD terminals to motor terminals.
5
Test Spindle Motor Directly
Temporarily run the spindle motor from the VFD panel (set Pd013=0 for panel control) and command a low speed (10Hz). If the spindle runs from panel but not from controller, the issue is in the signal wiring. If it doesn't run at all, the motor or VFD has failed.
For water-cooled spindles: also verify the water pump is running before testing. Most VFDs have a thermal protection input — if cooling water isn't flowing, it will prevent startup.
6
Check Cooling System for Water-Cooled Spindles
Water-cooled spindles require coolant flow before the VFD allows startup. Check: pump running (listen/feel), water tube not kinked or blocked, reservoir level, pump impeller not clogged. A blocked cooling system trips thermal protection.
Replace the HQB cooling pump if it's not circulating water. Al Azhar CNC stocks the HQB-800 and HQB-1500 pumps for same-day delivery.
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Frequently Asked Questions
The most common causes are: VFD alarm code (overcurrent or overload), missing signal from the controller (check AVI terminal wiring), wrong VFD parameter settings, or for water-cooled spindles, a failed cooling pump triggering thermal protection.
Common VFD alarms: OC (overcurrent — check motor wiring and spindle bearings), OV (overvoltage — check input power quality), OL (overload — spindle is mechanically loaded or motor is undersized), F001/Er.01 (communication error — check signal wiring).
Set VFD to panel control mode (Pd013=0 on most drives), then command a low speed (10–15Hz) from the panel. If the spindle runs, the VFD is working and the problem is in the signal wiring from the controller.
A humming spindle that won't rotate usually means a missing phase (one of the 3 wires U/V/W is disconnected), seized bearings, or the VFD is in single-phase test mode. Check all 3 phase connections to the motor first.
Check coolant level weekly, clean the reservoir monthly, and replace coolant every 6 months. In UAE's hot climate, coolant evaporates faster — check more frequently in summer. Use distilled water mixed with anti-algae coolant.
In most cases, VFD and spindle motor are replaced independently. If only the VFD alarm code shows (motor tests good), replace the VFD. If the motor windings are burned (confirmed by insulation resistance test), replace the motor. Al Azhar CNC can help identify the failed component.