C7085-90921 Chapter 5 Theory of operation 103
Basic operation
HP LaserJet 4500 series and 4550 series printer functions are divided into three systems: the image
formation system, paper pick-up feed system, and engine control system. These systems are
thoroughly described in this chapter.
Figure 5-1 Basic system operation
Paper feeder (option)
LASER/SCANNER SYSTEM
Scanning mirror
Laser
diode
Scanner
motor
BD
circuit
IMAGE
FORMATION
SYSTEM
Photo-
sensitive drum
Primary
charging roller
Cleaner unit
Developing
unit
Intermediate
transfer belt
Secondary transfer roller
ITB cleaning
roller
Cassette
Pick-
up
unit
Multi-purpose
tray
To external device (host computer, etc.)
through the video controller PCB
ENGINE
CONTROL SYSTEM
DC controller
PCB
Operation
panel
Cassette
PICK-UP/FEED SYSTEM
Face-up
tray
Fixing
unit
Duplexing unit (option)
Face-down tray
Cassette paper
pick-up unit
Connector PCB
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