Fanuc 366 Alarm -

Unplug the feedback cable and power on the machine. If the alarm code changes (e.g., to a "feedback disconnected" alarm), the amplifier may be okay, and the cable or pulse coder is the likely culprit. 3. Clean or Replace the Pulse Coder

To isolate whether the problem is the motor or the cable, try disconnecting the feedback cable. If the alarm changes to a "Serial Data Error" (like 368), the cable and amplifier's communication path might be okay, further pointing toward an internal motor encoder issue. MRO Electric Are you currently seeing this alarm on a specific axis (like X or Z), and does it happen during rapid movements or while the machine is Drive or encoder issue? - Fanuc CNC forum | Facebook fanuc 366 alarm

Remove the servo motor and rotate the shaft manually while watching the position screen. If the numbers do not change, the pulse coder or cable is definitely not sending signals. 2. Inspect the Feedback Cable The cable is often the weakest link in the system. Unplug the feedback cable and power on the machine