Service manual

Chapter 2
2-4
F-2-6
2.2 Laser Exposure
2.2.1 Overview/Configuration
2.2.1.1 Outline
0007-4973
The laser/scanner system forms a latent image on the photosensitive drum according to the VIDEO signals sent from the SCNT Board. This system consists of the
laser driver circuit, scanner motor, etc. They are integrated into the laser/scanner unit and controlled by the DCNT Board.
The laser scanner unit is illustrated in the figure below and the sequence is described in the following.
F-2-7
The laser/scanner unit adopted a "twin beam method" (Note) which scans two lines simultaneously with two laser diodes for high-speed laser scanning with the
motor revs restrained. The operation sequence of the laser/scanner unit is discussed in the following:
1) The DCNT Board rotates the four-sided mirror when a print command is sent from the SCNT Board, and then rotates the scanner motor.
2) When the scanner motor starts to rotate, the DCNT Board emits light from the laser forcefully with the LASER CONTROL signal and then starts to control the
rotation of the scanner motor.
3) The DCNT Board rotates the motor at a specified speed with the SCANNER MOTOR SPEED CONTROL signal.
4) The DCNT Board sends the VIDEO signals to the laser driver circuit after the rotational speed of the motor reaches its target value.
5) The laser driver PCB emits light from the two laser diodes according to these signals.
6) The two laser beams strike the four-sided mirror rotating at a specified speed through the collimator lens and cylindrical lens.
7) The laser beams reflected off the four-sided mirror focus on the photosensitive drum through the focus lens and reflective mirror located in front of the four-sided
mirror.
*The term "book position" refers to the position at which the
motor is accelerated to prepare for reading.
HP
Book
Position *1
shading position
read start position
1. gain correction*1
read end position
2. shift shading*2
3. original scan
SCNT BOARD
Cylindrical lens
Scanner
motor
Four-sided mirror
Focus lenses
Reflective
mirror
BD circuit
Laser driver
VIDEO signals
DCNT BOARD
SCANNER MOTOR
CONTROL signal
LASER CONTROL signal
VIDEO signals