Xerox Phaser 6250DT, Service Manual, Page: 41 / 467

2-2 Phaser 6250 Color Laser Printer Service Manual
Overview of the Phaser 6250 Color Laser
Printer Theory of Operation
Summary of the Printing Process
The Phaser 6250 Color Laser Printer is a ‘full-color laser printer’, that utilizes
electrophotographic recording principals to place a full color image onto the print
media. The system, contains a drum and developing unit for each color (yellow,
magenta, cyan and black (YMCK)), and places the toner image of each color onto
print media producing full-color prints through three transfer units (primary transfer
units IDT1 (2 ea) and secondary transfer unit IDT2 (1 ea)).
A summary description of the printing process is presented in the following Steps, see
the illustration on the following page as a reference:
1. Charging:
The charge roller (RTC) is negatively charged by the high voltage
power supply (HVPS) and is kept in contact with the drum surface to provide a
uniform negative charge on the drum as it rotates at a constant speed. This occurs
simultaneously for YMCK. The refresher is a conductive brush that is also
negatively charged by the HVPS to pick off any toner particles left on the drum
after image transfer to the IDT.
2. Exposure:
The laser unit emits laser beams in response to image data from the
Image Processor board. The laser beams are directed onto the drum surface
through a system of mirrors and lenses. A rotating polygonal mirror causes the
laser beams to scan the drum surface from end to end (axially) as it rotates. The
beams are turned on to print a pixel and off when no printing is required. The
negative charge on the drum surface is reduced at each point where the energized
laser beam strikes, to form an invisible electrostatic latent image on the drum
surface. This process is performed simultaneously for YMCK.
3. Development: Toner is electrostatically attached to the invisible latent image
on the drum surface to form the visible image on the drum. Toner is fed into the
developer using the agitator and auger. The toner and the carrier in the developer
form a homogeneous layer on the magnet roller in the developer. The magnet
roller turns against the surface of the drum and is kept at a constant negative
potential. At areas on the drum surface where the negative charge has not been
reduced by the impact of laser light, potential between the drum and the toner
particles is lower than that between the magnet roller and the toner particles. At
areas where the drum charge has been reduced, the potential between the
particles and drum is higher than between the magnet roller and toner particles
are attracted to the drum. A thin semiconductive sleeve on the magnet roller is
vibrated by an AC voltage to encourage migration of the toner particles to the
drum. When the toner particles attach to the drum, the negative charge of the
particles reduces drum potential at that point, thus reducing the attraction of
additional toner particles. This process is performed simultaneously for YMCK.
4. Primary Transfer (drum --> IDT1):
The toner image formed on the individual
drum surface is transferred onto the surface of the IDT1 (intermediate Drum
Transfer 1: intermediate transfer roller 1). There are two IDT1’s: one for yellow
and magenta and one for cyan and black. IDT1 is conductive and receives a high
positive charge from the HVPS. The negatively charged toner image on the drum