Okuma Alarm A-1121 – PSC Optical Scale Encoder Error
Okuma Alarm A-1121 indicates a problem with the PSC optical scale encoder used for position detection.
This alarm occurs when the CNC control detects an abnormal signal or communication error from the optical scale position encoder.
The PSC (Position Scale Control) optical encoder is responsible for providing precise position feedback for machine axes. It measures the exact movement of the axis using an optical scale and sends this information to the CNC control system. If the encoder signal becomes unstable, missing, or invalid, the control triggers Alarm A-1121.
Possible causes
Several issues may cause this alarm:
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Faulty optical scale encoder
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Contamination on the optical scale (oil, dust, coolant)
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Damaged or misaligned encoder head
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Loose or damaged encoder cable
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Electrical noise affecting the encoder signal
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Failure in the axis feedback electronics
What happens when this alarm appears
When Alarm A-1121 occurs, the CNC control cannot correctly determine the axis position.
To prevent positioning errors or potential machine damage, the control system may stop axis movement or disable certain machine functions.
Recommended actions
To troubleshoot this alarm, the following steps are recommended:
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Restart the CNC machine and check whether the alarm returns.
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Inspect the optical scale and encoder head for contamination or damage.
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Check encoder cables and connectors for loose or broken connections.
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Verify that the encoder head is properly aligned with the optical scale.
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Test the encoder system and axis feedback electronics if necessary.
Professional repair service
If the alarm persists, the problem may be related to a defective encoder system or faulty control electronics.
Our technicians specialize in Okuma CNC electronics diagnostics and repair, including encoder systems, control boards, and servo electronics.
