Canon LBP1760P, Service Manual

Page: 61 / 394

B. Laser Control Circuit
1. Outline
Figure 2-3-2
This circuit switches the laser diode ON and OFF at a constant intensity in response to the
/VDO signal sent from the video controller.
The /VDO signal sent from the video controller to the engine controller is sent as is to the
logic circuit in the laser driver IC.
When the VIDEO DATA ENABLE signal (/ENBL) sent from the microprocessor (CPU: IC501)
is “L,” the laser driver circuit turns the laser diode ON and OFF according to the /VDO signal.
As the beam intensity set value differs between 1200DPI and 600DPI, the LASER BEAM
INTENSITY SWITCHING signal (HALF) is set to “H” for 1200DPI and to “L” for 600DPI. The power
adjustment circuit in the laser driver IC switches the beam intensity.
2 - 23
CHAPTER 2
/VDO
Logic
circuit
Power
adjustment
circuit
Drive
circuit
J501-6
J51-11
Control
amplification
circuit
/ENBL J501-3
91
/ENBL
/LON
J501-4
93
/LON
/VDO J501-2
HALF J53-9 J501-5
43
P52
J501-1
J53-13
PD LD
Engine controller PCB Laser driver PCB
Laser driver IC
(Photo Diode)
(Laser Diode)
CPU
6
/PRNT J51-10
P67
GND
VCC
IC501
BD PCB
J53-8
J53-11
J53-10
J53-12
/BDI
J53-6
J551-2
96
/BDI
+5V