Samsung ML-451 Series Service Manual page 182

4. Alignment and Troubleshooting
6) Check the Main Board Harness Connection.
7) If the same problem happens after checking 1~6, replace the Finisher main board.
8) If the same problem happens after checking 7, replace the Finisher Stapler.
9) If the same problem happens after checking 8, replace the Finisher harnesses.
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