Overview Of The Phaser 3425 Laser Printer; Summary Of The Printing Process - Xerox Phaser 3425 Service Manual

Overview of the Phaser 3425 Laser Printer

Summary of the Printing Process

The Phaser 3425 Laser Printer is a desktop monochrome laser printer, applying the
principals of an electrophotographic system. The system, comprising a drum and
developing unit, places the toner image onto print media producing a monochrome
image.
The following procedures are summarized. The printing process is composed of the
following steps. See the illustration on the following page as a reference.
1. Charging:
The charge roller is negatively charged at approximately -1400 VDC
by the high voltage power supply (HVPS). The charge roller is kept in contact
with the drum surface to provide a uniform negative charge of approximately -
800 VDC on the drum surface as it rotates at a constant speed.
2. Exposure:
The laser unit emits laser beams in response to image data from the
Main 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 to approximately -250 VDC at each point where the
energized laser beam strikes, to form an invisible electrostatic latent image on the
drum surface.
3. Development:
applied to the supply roller and are then applied to the developer roller in a even
layer controlled by the metering blade. The developer roller turns against the
drum and the toner particles are attracted to the relatively positive latent image.
The toner forms a visible image on the drum surface.
4. Pre-Clean:
lowering the surface potential and thereby providing enhanced transfer efficiency.
5. Transfer: The finished toner image on the drum is transferred onto the print
media using the voltage supplied by the transfer roller. The conductive transfer
roller receives a high positive voltage (approximately +1000 VDC) from the
HVPS that puts it at a higher potential than the drum. Since the transfer roller is
located behind the print media, the toner image is attracted to the high potential
and deposits on the surface of the print media.
6. Fixing:
The finished toner image is impermanent and easily smeared. To fix the
image, the print media goes through the Fuser where it passes between a pressure
roller and the heat roller. The toner is fused onto the print media by the
combination of heat and pressure.
The heat roller is heated by a Halogen lamp. The roller surface temperature is
detected by a Thermistor. The information is fed back to the lamp control to
maintain a surface temperature of 185º C during printing and 145º C during
standby. If the thermistor detects a Fuser overheat condition, it disconnects AC
power to the Fuser.
7. Cleaning: After the image is transferred to the print media, a cleaning blade
inside the cartridge removes any remaining toner particles from the drum.
2-2
Negatively charged toner particles from the toner hopper are
The pre-transfer lamp exposes the developed suface of the drum
Phaser 3425 Laser Printer Service Manual