Service manual

Chapter 2
2-5
8) When the four-sided mirror rotates at a constant speed, the laser beam striking the photosensitive drum scans on the drum at a constant speed.
9) When the photosensitive drum rotates and the laser beam scans on the photosensitive drum, at each specified speed, a latent image is formed on the drum.
Twin beam method
Two laser diodes (LD1, LD2) are built into the laser unit. In one scanning operation, the laser unit emits light from the LD1 and LD2 and writes two lines simulta-
neously. This enables a two-fold printing at the same print speed.
F-2-8
2.2.2 Controlling the Laser
2.2.2.1 Outline
0008-1541
This control is utilized to turn on/off the two laser diodes (LD1, LD2) based on the LASER CONTROL signal sent from the DCNT Board.
The circuit diagram of the laser control is illustrated below.
F-2-9
The DCNT Board sends the VIDEO (VDO1, /VDO1, VDO2, /VDO2) signals for image formation and the LASER CONTROL (CNT0, CNT1, CNT2) signals for
changing the operation mode of the laser, to the logic circuit in the laser driver IC. The laser driver performs the laser control responsive to a combination of the
CNT0, CNT1, CNT2 signals.
T-2-4
The following four controls are performed with the LASER CONTROL signals:
1) Laser emission control
Operation mode CNT0 CNT1 CNT2 Details
Standby mode L L L Laser control off status
Print mode H H H Laser emission is executable according to the
VIDEO signals.
LD1 force on mode L H L Turns on the LD1 forcefully
LD2 force on mode H L L Turns on LD2 forcefully
LD force off mode H H L Turns off the LD1 and LD2 forcefully
LD1 scan line
LD2 scan line
Feed direction
Image areas
First scan
Second scan
Third scan
Fourth scan
Logic circuit
PD
LD1
DCNT Board
Laser driver circuit
Laser driver IC
IC102
ASIC
GND
VCC
BD circuit
/BDI
J116-2
J31-2
LD2
LD1
switching
circuit
VDO1
/VDO1
VDO2
/VDO2
CNT0
CNT1
CNT2
Standard voltage
Comparator
Sample
hold circuit
C18
C16
PDOUT
J11
-1
J102
-13
-2
-4
-8
-10
-12
-10
-6
-4
-11 -3
-5
-6
-7
-9
-8
-7
-3/9/12
-2/5/11
IC101
CPU
Comparator
Sample
hold circuit
+5V
LD2
switching
circuit