Canon imagePRESS C800 Series Troubleshooting Manual page 190

Chapter 1
4) Clean the Sensor Flag's surface side [A], back side [B], and the [C] part of the Fixing Inlet Guide (which comes in contact with the Sensor Flag) with lint-free
paper [1] moistened with alcohol.
5) Clean the Separation Plate [1] for inner delivery Unit with lint-free paper [2] moistened with alcohol.
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