The Fanuc encoder is one of the most critical components in a CNC servo system. When an encoder fails, it can cause axis alarms, inaccurate positioning, erratic movement, or a complete axis fault. This guide helps you identify a faulty Fanuc encoder and explains the replacement process.
What Does a Fanuc Encoder Do?
The encoder (also called a pulse coder) is mounted on the rear of the Fanuc servo motor. It provides real-time position and speed feedback to the CNC controller, allowing the system to precisely control axis movement. Without accurate encoder feedback, the CNC cannot control the axis safely.
Common Fanuc Encoder Alarm Codes
- Alarm 300 — APC Alarm (Absolute Pulse Coder): Battery backup failure in the absolute encoder. Replace the encoder battery or the encoder itself.
- Alarm 301 — APC Alarm: Communication Error: Faulty encoder or damaged encoder cable.
- Alarm 360 — Serial Pulse Coder A/D Conversion Error: Internal encoder failure — encoder replacement required.
- Alarm 361/362 — Serial Pulse Coder Communication Error: Check encoder cable and connector first. If cable is good, replace encoder.
- Alarm 364 — Soft Phase Alarm: Encoder signal quality issue — dirty encoder or end of encoder life.
How to Diagnose a Faulty Encoder
- Check the encoder cable: Inspect for physical damage, loose connectors, or broken shielding. Cable faults are the most common cause of encoder alarms.
- Swap with a known good encoder: If possible, swap the suspect encoder with one from a working axis to confirm the fault.
- Check the servo amplifier diagnostic screen: The Fanuc servo diagnostic screen (Diagnosis page) shows the actual encoder feedback value — erratic values indicate a faulty encoder.
- Inspect the encoder physically: Check for oil contamination, physical damage, or a loose mounting.
Common Fanuc Encoder Part Numbers
- A860-2020-T301 — αi Series 1,000,000 pulse encoder
- A860-2000-T301 — αi Series encoder
- A860-0360-T201 — βi Series encoder
- A860-0309-T302 — Pulse coder for older series
Encoder Replacement Procedure
- Power OFF the machine and lock out / tag out the main power supply.
- Note the current axis position (or home the axis before shutdown if possible).
- Disconnect the encoder cable from the servo amplifier and from the motor.
- Remove the encoder from the servo motor (usually 3-4 screws on the encoder cover).
- Install the new encoder and reconnect the cable.
- Power ON and perform a reference point return (zero return) to re-establish the absolute position.
- Verify axis movement and check for encoder alarms.
New vs Used Encoders — What to Buy
For critical production machines, we recommend a new encoder for maximum reliability. For budget-sensitive applications, tested used encoders are a cost-effective option — especially for older machines where a new encoder may cost more than the machine is worth.
At JJ Automation, we supply both new and tested used Fanuc encoders, all verified before dispatch. We also offer encoder replacement services on-site across India.
- 📞 Call/WhatsApp: +91 8802212394
- ✉ Email: jj.automation@outlook.com
- 🌐 Browse encoders: www.jjautomation.in