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SV0447 and SV0448 are the most common encoder alarms on Fanuc servo systems used in press applications. They look similar but have different root causes.
## SV0447: Soft Phase Alarm
This is a software-detected phase error in the encoder signal. The drive detected that the A/B phase relationship is wrong.
Common causes on press applications:
- Encoder cable damaged at the slide flex point
- Incorrect cable type (using standard cable instead of flex-rated)
- EMI from the press drive affecting the encoder signal
Diagnosis:
1. Check the encoder cable at the point where it enters the slide housing - this is the highest-flex point
2. Flex the cable manually while monitoring the alarm: if it triggers during flexing, the cable is damaged internally
3. Check the cable shield connection at the amplifier end
4. Verify the cable is routed away from the main power cables
## SV0448: Hard Phase Alarm
This is a hardware-detected phase error. More serious - usually means the encoder itself is failing or there is a hardware fault in the feedback circuit.
Diagnosis:
1. Swap the encoder cable first (eliminates cable as cause)
2. If alarm persists, check the encoder connector at the motor: look for moisture, corrosion, or bent pins
3. Measure encoder supply voltage at the motor connector: should be 5V +/- 0.25V
4. If voltage is correct and cable is good, the encoder needs replacement
## Fanuc-Specific Notes for Press Applications
- Parameter 2064 sets the encoder feedback filter. On high-vibration press applications, increasing this value (default 0, try 1 or 2) can reduce false alarms
- Use Fanuc A66L-0001-0284 cable for flex applications, not standard A66L-0001-0283
- After encoder replacement, perform the reference position return procedure before running production