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The A.810 and A.820 alarms on Yaskawa Sigma-7 drives are encoder-related faults that show up frequently on servo press applications. Here is how to diagnose and fix them.
## A.810: Encoder Backup Error
This alarm means the encoder lost its absolute position data. Causes:
- Backup battery voltage dropped below 2.8V
- Battery was disconnected while encoder was unpowered
- Encoder cable was disconnected with power on
Fix sequence:
1. Replace the battery (Yaskawa part: JZSP-BA01)
2. Clear the alarm: set Pn008.0 = 1, cycle power
3. Perform absolute encoder setup: Fn008 in the drive utility
4. Re-establish the home position on the press
5. Run 10 dry cycles and verify position repeatability
Note: After A.810, always verify the home position before running production. The encoder has lost its reference.
## A.820: Encoder Checksum Error
This alarm indicates corrupted data in the encoder communication. More serious than A.810.
Causes:
- Electrical noise on the encoder cable
- Damaged encoder cable (especially at flex points near the slide)
- Failing encoder
- Loose connector at the encoder or drive end
Diagnosis sequence:
1. Check cable routing: is it running parallel to power cables? Minimum separation should be 300mm
2. Check cable shield: measure continuity from encoder end to drive end, should be under 1 ohm
3. Check connector pins: look for bent pins, corrosion, or loose crimps
4. Swap the encoder cable with a known-good cable and see if the alarm clears
5. If alarm persists with new cable, the encoder itself is failing
## Preventing Recurrence
For servo press applications specifically:
- Use Yaskawa-recommended cable (JZSP-CHP800 series) for flex applications
- Add a cable carrier (energy chain) if the cable flexes more than 90 degrees
- Set Pn520 (excessive position deviation alarm level) to match your application
- Log encoder temperature: Sigma-7 encoders report temperature via Fn011