Yaskawa A1000 LF2 Fault — What It Means
The LF2 fault on a Yaskawa A1000 variable frequency drive indicates output current imbalance. This means one or more of the three output phases feeding the motor is missing or carrying significantly less current than the others. The drive detects this condition on the motor output side and shuts down to protect both itself and the motor from damage.
The imbalance can originate from a loose or damaged connection at the drive’s output terminals, a broken or burnt conductor in the motor cable, or an internal fault in the motor windings themselves. Less commonly, the drive’s own output circuit or control board may be damaged. The fault appears after the drive has attempted to run and sensed unequal current flow across the three output phases.
Before You Replace Anything
Technicians sometimes replace the entire drive or control board before checking wiring. Measure line-to-line motor winding resistance and retorque all output terminals to specification before ordering expensive electronics.
Common Causes
- Loose output terminal connections (~40%) One or more lugs on the drive’s U, V, or W output terminals are not tightened to the torque specification in the manual, creating high resistance or intermittent contact.
- Damaged motor cable or missing phase conductor (~30%) A broken wire, burnt insulation, or pinched cable between the drive and motor causes one phase to drop out or carry reduced current.
- Unequal motor winding resistance (~20%) The motor has a shorted turn, open winding, or internal phase imbalance that causes unequal current draw even when all three drive outputs are healthy.
- Failed drive output circuit or control board (~10%) Internal damage to the drive’s IGBT module, gate driver, or current-sensing circuit prevents one or more output phases from switching properly.
Quick Diagnosis
Answer these to narrow it down fast.
With power off and locked out, are all three output terminal lugs tight and free of scorch marks or discoloration?
No: Retorque all output terminals to the drive manual's specification and inspect for burnt or damaged lugs. Replace any damaged hardware before re-energizing.
Do all three line-to-line motor winding resistance measurements (U-V, V-W, W-U) match within a few percent?
No: Motor has an internal winding fault. Disconnect the motor and test it separately or replace the motor.
Does the fault clear when you disconnect the motor leads at the drive and run the drive into a known-good test motor or resistive load?
No: The drive's output circuit or control board is damaged. Replace the control board or drive as recommended by Yaskawa service.
Step-by-Step Fix
- Verify the fault and history by navigating the drive’s keypad to view active and stored alarms. Record the fault code, timestamp, and any conditions present when LF2 appeared.
- De-energize the drive and apply lockout/tagout to both incoming AC power and any control circuits. Wait for DC bus capacitors to discharge fully before opening the enclosure.
- Inspect all three output terminals (U, V, W) for loose lugs, burnt marks, corrosion, or broken strands. Look for discoloration on terminal blocks or cable insulation near the connection points.
- Retorque each output terminal lug to the tightening torque specified in the A1000 installation manual for that terminal block size. Use a calibrated torque wrench or torque screwdriver.
- Measure line-to-line resistance of the motor windings at the motor terminal box using a digital multimeter. Compare U-V, V-W, and W-U readings. All three values should match closely.
- Disconnect the motor cable at the drive and inspect the cable run for physical damage, pinch points, or signs of overheating. Test insulation resistance from each phase to ground and phase-to-phase if cable damage is suspected.
- If wiring and motor tests pass, suspect internal drive damage. Consult Yaskawa technical support or a qualified drive repair center. Replace the control board or entire drive if the fault persists after all external checks.
- Restore power and test only after confirming all connections are torqued, all covers are secured, and the motor and cable have passed resistance checks. Monitor drive current display during startup for balance across all three phases.
Parts Often Needed
| Part | Notes |
|---|---|
| Motor output cable | Amazon | If cable insulation is damaged or conductors are broken. Match cable gauge and length to original specification. |
| Three-phase AC motor | Amazon | If winding resistance is unequal or motor windings are open or shorted. Must match drive nameplate voltage and motor load rating. |
| Yaskawa A1000 control board | Amazon | Field-replaceable PCB for the A1000 series. Order by drive model and serial number if output circuit fault is confirmed and wiring/motor are verified good. |
When to Call a Pro
Call a qualified industrial electrician or drive specialist if you are not trained in lockout/tagout, high-voltage DC bus safety, or VFD troubleshooting. The A1000 stores lethal voltage on internal capacitors even after AC power is removed. Professional diagnosis is required to safely measure motor winding resistance, perform insulation resistance tests on long cable runs, and determine whether the fault lies in the drive’s internal output circuit or external wiring. If the drive or control board needs replacement, a certified Yaskawa service center can provide factory-calibrated parts and make sure the replacement is configured correctly for your motor and application. Do not attempt to open the drive or disconnect motor leads under power.
Rough cost: A pro service call runs about $150-500 depending on whether the fault is wiring, motor cable, or internal drive damage.