How to Replace the Pulse Coder (Encoder) on a Fanuc Servo Motor

Fanuc servo motor encoders (pulse coders, A860-xxxx series) fail from coolant ingress, vibration and age — and the machine tells you with alarms like the SV/APC 300-series (absolute position lost), pulse coder communication errors, or a motor that hunts and vibrates. The good news: on most Fanuc motors the pulse coder is a bolt-on part you can replace without changing the whole motor.

Before you start

• Confirm it's really the coder: swap-test with the cable and amplifier in mind — a damaged feedback cable or amplifier fault mimics coder failure. Inspect the cable and connector pins first.
• Get the exact replacement: the coder model is on its label (e.g. A860-0360-T001, A860-2020-T301 and similar). Coders differ (incremental vs absolute, pulse counts, serial types) — the replacement must match, or a compatible substitute confirmed. Send us the number if unsure.
• Back up parameters and note your grid-shift/reference data if available.

Step-by-step

1. Power OFF and lock out. If the axis can drop under gravity (Z axis), support or block it first — releasing a motor with a brake on a vertical axis without support is how crashes happen.
2. Access the motor — remove covers as needed. Many coders can be changed with the motor in place; if not, remove the motor (see our motor replacement guide).
3. Disconnect the encoder connector (cannon plug or clip connector) from the coder.
4. Remove the coder cover / rear housing screws and withdraw the pulse coder from the motor rear. Note how the drive coupling (Oldham coupling / keyed spigot) engages the motor shaft.
5. Fit the new coder, aligning the coupling exactly as the old one sat. Do not force it — it should seat cleanly.
6. Reconnect, power on, and clear the alarms (APC alarms typically need the alarm-clear/battery-reset procedure).
7. Re-master the axis: with an absolute coder replaced, the machine has lost its zero. Perform reference-point return / absolute zero mastering per your machine's procedure, and verify against a known position before cutting.

Parts & help

• Fanuc pulse coders & encoders
• How to identify a faulty Fanuc encoder
• Fanuc servo motors