Canon imagePRESS C800 Series, Troubleshooting Manual

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Chapter 1
1-41
1.1.1.6.14 Stain on image 264mm behind high-density image due to intensive use of B/W mode
0031-8837
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Symptom
If more than 50,000 sheets of output is made in black and white mode, stain [a] may appear on image 264mm behind high-density image.
The arrow [b] indicates the feed direction.
The symptom is more likely to occur with linty paper or when a same size is used repeatedly.
Cause
Frequent use of black and white mode allows paper lint to accumulate gradually at the nip of the drum cleaning blade [b] that is contacting with the drum [a].
Especially the front side and the rear side corresponding to the paper edges are prone to pile up more lint.
At the part where paper lint is piled up, toner passes through the drum cleaning blade and stagnates at the back side [c] of the blade.
When a high-density image is transferred primarily, discharging phenomenon [d] is generated at a spot where there is a difference of density of toner.
The part of the drum where the discharge phenomenon was generated is developed with the toner [e] piled up at the back of the drum cleaning blade, and it is
transferred to the paper after the high-density image went around the drum once and results in the symptom.
Service work
1) Refer to the service manual "Parts Replacement and Cleaning > Image Formation Sytem > Removing the Drum (Bk) > Procedure" to remove the drum (Bk).
[Caution] Underlay some sheets of paper and the like beneath before laying the drum (Bk).
2) Disconnect the connector [4], remove the 6 screws [2] to remove the drum cleaning unit.
Fit the 2 bosses [3] to attach it back.
[Caution]
-Cover the drum (Bk) with a drum protection sheet or paper (of 5 sheets or more) to block out light.
-As the drum cleaning unit [1] is covered with toner, underlay some sheets of paper and the like and turn the unit upside down on the sheets.