Xerox PHASER 7500, Service Manual

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Phaser 7500 Printer Service Manual 2-9
Theory of Operation
Development
The electrically charged toners adhere to the electrostatic latent image on the
Drum surface to form a visible image (a toner image that can be seen) on it. This is
performed in parallel for each color - Yellow, Magenta, Cyan, and Black.
• The Toner in the Cartridge is transported into the Developer Housing
Assembly by the Agitator and Auger that are driven by the Dispense Motor.
• The Toner and the Developing Beads (toner + carrier) in the Developer
Housing Assembly is agitated by the Auger, and then supplied to the Magnet
Roll that is located close to the Drum surface. Friction generated by the
agitation charges the toner and the carrier (toner becomes negative and
carrier becomes positive) and causes them to stick together by mutual
electrical attraction. Since the carrier is a magnetic substance, it is attracted to
the magnetized Magnet Roll and formed into an even layer by the Trimmer.
• The Magnet Roll surface is covered with thin semi-conductive sleeve. DB
(Developing Bias) voltage is supplied from the HVPS to this semi-conductive
sleeve. The DB voltage consists of overlapping AC voltage and negative DC
voltage.
The DC voltage is used to maintain the Magnet Roll at a constant negative
potential compared to the Drum conductive layer. Therefore, sections of Drum
surface where the negative charges have not been reduced will have lower
potential than the Magnet Roll, while sections where the negative charges
have been reduced will have higher potential than the Magnet Roll.
The AC voltage is used vibrate the toner on the Magnet Roll surface so that it
can be transferred more easily. Hence, the negatively charged toner is only
attracted to the sections with reduced negative charges on the Drum surface
(the electrostatic latent image) to form a toner image on the Drum. (Since the
attraction of the positive charge on the Drum conductive layer is stronger
than the repulsive force of the negative charge on the Drum surface, the toner
still gets pulled to the Drum despite being affected by repulsive force of the
s7500-344
Toner Cartridge
Dispense Motor
Agitator
Auger
Developer Housing
(Developer Housing Assembly)