Applicable Systems
Series 0i
Series 16/18/21
Alpha
Beta
Symptoms
The CNC system displays alarm 414: SERVO ALARM: n-TH AXIS - DETECTION RELATED ERROR. The digital servo system has detected a fault related to the position detection system. The diagnostic display No. 200 and No. 204 should be checked for detailed information.
Possible Causes
- Pulse coder (encoder) signal error or disconnection
- Serial feedback cable damaged or poorly connected
- Pulse coder internal failure (LED, disk, or sensor)
- Servo amplifier detection circuit malfunction
Troubleshooting Steps
- Step 1: Check diagnostic display No. 200 for the specific detection error bit
The diagnostic screen shows which aspect of the detection system is faulty - Step 2: Inspect the serial feedback cable between the motor encoder and the amplifier
Cable should be intact, properly seated, and the locking connector engaged - Step 3: Swap the feedback cable with a known-good one
If the alarm follows the cable, the cable is faulty; if it follows the motor, the encoder is faulty - Step 4: Check diagnostic display No. 204 for the amplifier-side detection status
This screen shows whether the amplifier detects the encoder signal correctly
How to Reset
To reset: 1) Fix the cable or encoder issue. 2) Press RESET. 3) Re-reference the axis. Caution: Detection errors can cause the axis to lose position accuracy. Always re-reference (home) the axis after clearing this alarm.
Common Replacement Parts
- A860-2000-T301: FANUC serial pulse coder cable (Match the cable length and connector type to the original; use FANUC genuine cables for reliable high-speed serial communication)
Frequently Asked Questions
- Q: What diagnostic screens should I check for alarm 414?
Check DGN No. 200 for the detection error detail bits and DGN No. 204 for the detection status. These screens show exactly which part of the detection system is problematic (e.g., disconnection, phase error, CRC error).
- Q: Can I replace just the encoder on a FANUC motor?
On some motor models, the encoder is replaceable. On others (especially built-in encoders), the entire motor may need replacement. Always consult the motor's maintenance manual for encoder replacement procedures.
Source: FANUC Series 0i-Mate Maintenance Manual, B-64115EN
Category: PLC & VFD