Yaskawa A1000 AL-08 — What It Means
AL-08 is an alarm (not a hard fault) that appears on Yaskawa A1000 drives operating in Closed Loop Vector or speed feedback mode. It indicates the drive has detected that encoder feedback signals are missing, unstable, or not properly received from the motor-mounted encoder. The drive may continue running but with degraded performance or loss of precise speed regulation. This alarm typically occurs when the encoder interface cannot establish or maintain communication with the position encoder, which the drive needs for accurate motor control in vector mode.
Before You Replace Anything
Technicians sometimes replace the encoder option card or the encoder itself before checking the cable. Test cable continuity and inspect terminations at both the drive and motor ends first, which costs nothing and finds most problems.
Common Causes
- Broken or loose encoder cable (~45%) Physical damage, loose terminations, or unplugged connectors interrupt signal transmission between encoder and drive.
- Encoder interface option card not seated (~20%) The encoder option card (such as PFW-ENC or PFW-ENC2) is loose in its slot or has corroded edge contacts.
- Faulty encoder unit (~15%) Internal encoder failure, contamination, or moisture damage prevents signal generation at the motor.
- Incorrect wiring or pinout (~10%) Reversed signal wires, shorted conductors, or wrong pin assignments at cable terminations block proper communication.
- Encoder power supply failure (~7%) Insufficient voltage (typically 5V or 12V) to the encoder from the option card or external supply prevents operation.
- Drive parameter mismatch (~3%) Closed Loop Vector mode is enabled but encoder type or resolution parameters (C5-01, C5-02, C5-03) are incorrectly configured.
Quick Diagnosis
Answer these to narrow it down fast.
Does the alarm clear after reseating the encoder cable connectors at both the drive option card and motor ends?
No: Proceed to test cable continuity with a multimeter to find breaks or shorts.
With power off, does the encoder cable show continuity on all signal wires and no shorts to ground?
No: Replace the encoder cable. Inspect for pinch points or cable routing issues that caused the damage.
After swapping in a known-good encoder option card, does AL-08 still appear?
No: The original option card was defective. Install the replacement card and verify drive parameters.
Step-by-Step Fix
- Power down the VFD and motor by opening the main disconnect and waiting for DC bus discharge (consult your drive manual for safe discharge time).
- Inspect encoder cable terminations at both the drive option card end and the motor peckerhead or encoder housing, looking for loose pins, corrosion, melted insulation, or unplugged connectors.
- Test cable continuity using a multimeter by measuring resistance between each signal wire pair (typically less than 10 ohms for a good connection) and checking for shorts to ground or between conductors.
- Reseat the encoder option card by removing it from its slot in the drive, inspecting edge contacts for corrosion or damage, and firmly reinstalling it until it clicks into place.
- Verify encoder power supply by measuring DC voltage at the encoder connector (typically 5V or 12V depending on encoder model) with power on and the drive in ready state.
- Check drive parameters by reviewing C5-01 (encoder type), C5-02 (encoder pulses per revolution), and C5-03 (encoder direction) to confirm they match the installed encoder specifications.
- Swap the encoder or option card if all wiring and parameters are correct but the alarm persists, starting with the option card since it is easier to access than the motor-mounted encoder.
Parts Often Needed
| Part | Notes |
|---|---|
| Yaskawa encoder cable | Amazon | Match length and connector type to your motor and drive installation, shielded cable required |
| Yaskawa encoder interface option card (PFW-ENC or PFW-ENC2) | Amazon | Verify compatibility with your A1000 drive model and encoder type before ordering |
| Incremental encoder (motor-mounted) | Amazon | Must match motor shaft size, mounting flange, and pulse-per-revolution rating specified in drive parameters |
When to Call a Pro
Call a qualified VFD technician or controls electrician if you are not trained in variable frequency drive troubleshooting or if the drive operates in a critical process. Work on encoder systems requires understanding of signal integrity, proper cable shielding, and correct parameter configuration. If you lack a multimeter, spare option card, or experience with encoder wiring, professional diagnosis will save time and prevent damage to the drive or motor. High-voltage hazards remain present inside the drive even after power-down until the DC bus fully discharges, so always follow lockout-tagout procedures and consult the technical manual.
Rough cost: A pro service call runs about $200-500.