Canon imageRUNNER ADVANCE C3330 Series Service Manual page 333

3. Remove the seal [1] from the supply mouth.
4. Check that the connector is hooked on the groove in the cover.
If it is not hooked, the connector may get stuck when inserting the Developing Unit.
5. Insert the Developing Unit up to the position in the figure below.
CAUTION:
Take care to prevent the connector of the Developing Unit from getting caught.
6. Disconnect the connector [1] from the groove in the cover, and connect it to the Developing Unit.
[1]
[1]
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4. Parts Replacement and Cleaning