Yaskawa A1000 AL-12 Fault — What It Means
The AL-12 fault code does not appear in official Yaskawa A1000 documentation. You are most likely encountering Er-12 (Current Detection Error) on a Yaskawa V1000 series drive, which is often confused due to naming similarities, or you have misread a different A1000 code such as LT-2 (Overtemperature) or UV3 (Under Voltage). Er-12 means the drive has detected a missing motor phase (open circuit) or that motor current has exceeded the drive’s rated limit. The drive’s internal current detection circuit reports a signal error, typically because current is too low due to phase loss or because an auto-tuning attempt was made without a motor connected. If you are certain your drive is an A1000 and the display shows AL-12, consult your specific model’s manual or wiring diagram, as the exact meaning may vary by firmware revision or regional version.
Before You Replace Anything
Technicians often replace the entire drive or control board without first checking motor wiring and phase resistance. Measure resistance between each motor phase (U-V, V-W, W-U) with a multimeter to confirm all phases are present and balanced before replacing any internal components.
Common Causes
- Open motor phase (~45%) A broken wire, loose connection, or blown fuse in one of the three motor phases (U, V, W) prevents current flow and triggers the detection error.
- Loose or corroded wiring (~25%) Connections at the drive output terminals or motor terminal box are not tightened or have developed corrosion over time.
- Auto-tuning without motor (~15%) Attempting Auto-Tuning (parameter C5-01) without the motor wired to the drive causes the current detection circuit to report an error.
- Phase-to-phase short (~10%) A short circuit between motor lines causes abnormal current flow and trips the current detection error.
- Faulty control board (~5%) The current detection signal on the control board is damaged or malfunctioning, reporting false phase-loss even when wiring is correct.
Quick Diagnosis
Answer these to narrow it down fast.
Are all three motor output terminals (U, V, W) tight and free of corrosion?
No: Tighten all loose terminals and clean any corrosion. Restart the drive and see if the fault clears.
Do resistance readings between U-V, V-W, and W-U show nearly equal values (within 5 percent)?
No: One phase is open or shorted. Inspect the motor cable for damage and replace if necessary, or check the motor windings.
Did the error occur immediately after running auto-tuning?
No: The fault is unrelated to auto-tuning. Focus on motor wiring integrity and phase resistance measurements.
Step-by-Step Fix
- Power down safely. Turn off the drive and disconnect mains power. Wait for the CHARGE indicator light to extinguish or measure DC bus voltage to confirm it is below 5 V DC.
- Inspect motor wiring. Check all U, V, W connections at the drive output terminals and motor terminal box. Tighten any loose terminals and clean corrosion.
- Measure motor phase resistance. Use a multimeter to measure resistance between U-V, V-W, and W-U. Resistance values should be nearly equal (within 5 percent tolerance). If one reading is infinite, you have an open phase.
- Check phase-to-ground resistance. Measure resistance from each phase (U, V, W) to the motor frame. Readings should be greater than 1 MΩ. Lower values indicate a ground fault.
- Verify auto-tuning setup. If the error occurred during auto-tuning, confirm the motor is wired to the drive and run the auto-tuning sequence again from parameter C5-01.
- Reseat gate driver connector. If wiring and resistance checks pass, power down the drive, open the control panel, and reseat the CN13 connector on the gate driver board.
- Replace control board. If all external wiring and motor resistance are confirmed good and the fault persists, the current detection circuit on the control board is likely faulty and the board must be replaced or the entire drive swapped.
Parts Often Needed
| Part | Notes |
|---|---|
| Motor cable (U, V, W shielded) | Amazon | Match cable gauge and length to your drive and motor ratings. |
| Yaskawa control board (model-specific) | Amazon | Confirm your exact drive series (A1000 vs. V1000) and frame size before ordering. |
When to Call a Pro
Call a qualified electrician or VFD technician if you are not comfortable working with high-voltage DC bus circuits (which can remain energized even after AC power is removed), if you do not own a multimeter or know how to measure phase resistance safely, or if wiring and motor checks pass but the fault persists. A pro can safely measure DC bus voltage and ripple, reseat internal connectors, and replace control boards or gate driver assemblies without damaging other components. If your facility has explosion-proof or hazardous-location equipment, only a certified technician should open the drive enclosure.
Rough cost: A pro service call runs about $150-400 for wiring repair or control board replacement.