Canon 3370 Series Service Manual page 32

Chapter 2
Engine
controller PCB
+5V
IC201
CPU
/CNT0
/CNT1
/CNT2
/BDO
/BDI
The DC controller sends the VIDEO signals (VDO1, /VDO1, VDO2, /VDO2) and the LASER CONTROL signals (CNT0, CNT1, CNT2) to the logic circuit in the
laser driver IC. The VIDEO signals are for image formation and the LASER CONTROL signals are for switching the operational modes of the laser. The laser
driver IC controls the laser according to the combination of the CNT0, CNT1, and CNT2.
The table below indicates combinations of the LASER CONTROL signals (CNT0, CNT1, CNT2).
Operation mode
Discharge mode
Data output mode
LD1 APC mode
LD2 APC mode
Force LD1, LD2 ON
Force LD1, LD2 OFF
This control incorporates the LASER CONTROL signals for the following 4 controls:
1) Laser emission control
2) Automatic power control (APC)
3) Horizontal synchronization control
4) Image masking control
2-4
Video
controller PCB
J201 J801
-12 -14
VDO1
/VDO1
VDO2
/VDO2
-16
-20
CNT0
-19
CNT1
-18
CNT2
-14
-17 -13
CNT2
L
H
L
L
H
L
VCC
-6 LD1
switching
-5
circuit
-8
-9
Comparator
-7
GND
C802
Sample
hold circuit
-1
-2
-3
F-2-4
T-2-2
CNT1 CNT0
L
H
H
L
L
H
Laser driver PCB
LD1 PD LD2
LD2
switching
circuit
Comparator
Reference
voltage
Sample
hold circuit
Logic circuit
Laser driver IC
BD PCB
Remarks
L C802, C803 discharge
H Used during normal printing
L Used during LD1 APC mode
H Used during LD2 APC mode
L Used during test printing
H Used during image masking period
C803