Samsung ML-451 Series Service Manual page 171

4. Alignment and Troubleshooting
4) Check the Safety Unit's operation using Rear Jogger. The same "switch ON/OFF" operation should be followed.
5) Check the Safety Unit's operation. When Rear Jogger stands at the position having the Shield and Rear Jogger met,
the Safety Switch should be ON.
6) If the same problem happens after checking 1~5, Replace the Finisher main board.
7) If the same problem happens after checking 6, Replace the Finisher harnesses.
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