Brother HL-4000CN Service Manual page 87

1.3.4 Primary transfer (drum -> IDT 1)
In the primary transfer process, toner image formed on the drum surface is transferred
onto the surface of the IDT 1 (Intermediate Drum Transfer 1: intermediate transfer roll 1).
Two IDT 1 are provided: yellow and magenta, and cyan and black are respectively
transferred to their IDT 1.
IDT 1 is a conductive roll and receives supply of high positive voltage from HVPS.
The toner image (negatively charged) on the drum is attracted to the IDT1 positively
charged, and transferred from the drum to the IDT1 surface.
At this time, electric charge of the drum surface is neutralized by the IDT1.
Drum surface
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Drum (Y)
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Fig.3-16
Drum (M)
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Drum (C)
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Drum (K)
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III-9
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+ +
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IDT1
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+ +
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+ +
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IDT1
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Fig.3-15
: Negative electric charge
: Positive electric charge
: Toner
HVPS