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FANUC Controller
Power Supply · Basic · 15-30 minutes
Fanuc Alarm 446 - Encoder Battery Voltage Low
Alarm 446 HARD DISCONNECT indicates complete loss of pulse coder (encoder) feedback signal on the specified axis. This is a critical fault where the servo amplifier has detected total absence of position feedback, typically caused by pulse coder cable damage, loose connections at JD1A/JD1B connectors, failed pulse coder unit, or loss of 5VDC power supply to the encoder.
446
Fanuc Alarm 446 - Encoder Battery Voltage Low
Encoder Battery Low
Memory battery encoder battery low. The CNC memory backup battery voltage is low and requires replacement to prevent data loss.
Root Cause Summary
Alarm 446 HARD DISCONNECT indicates complete loss of pulse coder (encoder) feedback signal on the specified axis. This is a critical fault where the servo amplifier has detected total absence of position feedback, typically caused by pulse coder cable damage, loose connections at JD1A/JD1B connectors, failed pulse coder unit, or loss of 5VDC power supply to the encoder.
Safety
- Keep power on during battery change
- Position will be lost if power off
Causes and Fixes
- 1
Power off CNC and verify pulse coder cable connections at motor JD1A/JD1B connectors and amplifier CN2 connector. Inspect for bent pins, contamination, or loose locking mechanisms.
Disconnect all power before inspecting motor connections to prevent electric shock.
- 2
Inspect pulse coder cable along entire length for pinch points, cuts, excessive flexing near cable carriers, or damage from swarf/coolant. Replace cable if any damage is visible.
- 3
Measure cable continuity with multimeter between motor JD1A pins and amplifier CN2 pins per connection manual. Check all signal pairs: A/A-, B/B-, Z/Z-, and 5V/GND.
- 4
After reconnection, navigate to DIAGNOSIS > SERVO and check DGN300-307 (serial pulse coder data) or DGN400-407 (position deviation) to verify encoder signals are being received.
Call a technician if:
- ·Servo amplifier replacement required
- ·Encoder replacement on sealed motor
- ·Complex EMI troubleshooting needed
Prevention
- Regular encoder cable inspection
- Proper cable routing away from EMI sources
- Maintain clean, dry electrical connections
- Monitor encoder power supply voltages during PM
Common Mistakes
- Testing encoder signals with power on
- Ignoring cable shield grounding requirements
- Using non-genuine replacement encoders
- Overlooking EMI sources during troubleshooting
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