Canon imageRUNNER C1335 Series Service Manual page 361

■ Dark spots on halftone image
[Location]
The ITB being in the initial phase (the surface resistance is high), and the drum unit being in
the terminal phase of its use (the electric charge of toner is low).
[Cause]
When a halftone image is output, dark spots may appear locally. This symptom does not
occur with black color.
A tiny amount of black developing carrier[1] is usually on the surface of the black drum[2].
When the color toner image[a] on the ITB[3] passes the Y drum, the M drum, and the C drum
and reaches the Black drum[2], a portion of the surface of the color toner image[a] is slightly
transferred onto the Black drum[2] (This transferring symptom is hereinafter referred to as
retransferring).
In the image portion[b] where the developing carrier on the surface of the Black drum[2] is
positioned, less amount of toner is retransferred. On the contrary, the portion[c] on the ITB[3]
side, which corresponds to the position of the developing carrier, projects like a heap with
more toner. Accordingly, when the toner image on the ITB[3] is secondary transferred to
paper, the portion[c] of the heap appears as a dark spot on the image.
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Troubleshooting > Troubleshooting Items > Image Failure > Dark spots on halftone image
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6 Troubleshooting > Troubleshooting Items > Image Failure > Dark spots on halftone image
[Condition]
The symptom tends to occur under a combination of conditions including a low humidity
environment, the ITB being in the initial phase (the surface resistance is high), and the drum
unit being in the terminal phase of its use (the electric charge of toner is low).
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[a]
[c]
[3]
[b]
[1]
[2]
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