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Encoder faults are among the most disruptive issues on a servo press line.
## Common Encoder Fault Codes
- Yaskawa: A.810 Encoder Backup Error, A.820 Encoder Checksum Error
- Fanuc: SV0447 Soft Phase Alarm
- Mitsubishi: AL.16 Encoder error
- Siemens: F31117 Motor encoder signal level fault
## Step 1: Check the Cable First
Before touching the encoder, inspect the feedback cable for pinch points near the slide, bent pins or corrosion at connectors, and shield continuity under 1 ohm end-to-end. If the press has run 3+ years, replace the cable as a precaution.
## Step 2: Check Battery Voltage
Absolute encoders retain position via a backup battery. When it drops below 3.0V you get backup errors. Replace every 3-5 years. After replacement perform a home position reset. Never replace with encoder powered off more than 30 seconds.
## Step 3: Verify Encoder Supply Voltage
Most encoders run on 5V DC. Acceptable range: 4.75V to 5.25V. Below 4.5V the encoder will malfunction intermittently. For cable runs over 10 meters use 24V encoders.
## Step 4: Check for Electrical Noise
Route encoder cables at 90 degrees to power cables. Ground the shield at one end only, at the drive end.
## After Repair: Home Position Verification
Jog slide to mechanical top dead center. Compare encoder position to stored home value. If they differ by more than 0.1mm re-teach home position. Run 5 dry cycles and monitor repeatability.