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A servo press uses servo motors for precise force and position control during forming operations.

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Use our free tonnage calculator at servopress.club/tonnage-calculator.html

Yaskawa Sigma-7 Drive on Servo Press: A.810 and A.820 Alarm Troubleshooting

admin

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

anna_controls

A.810 is almost always the battery. Replace it and the alarm clears after a power cycle. But A.820 is more serious —it means the encoder's internal checksum failed, which usually means the encoder itself is failing. Don't just clear it and keep running. Replace the encoder before it fails completely mid-stroke.

raj_maintenance

We keep spare encoder batteries in every press cabinet and changed our replacement schedule from 3 years to 2 years after getting burned twice. The batteries cost $15 each. The downtime from a dead battery on our line runs about $5,000 per incident including the service call and lost production. We label each battery with the install date using a permanent marker so anyone can see at a glance how old it is.