Canon CLBP-460PS, Service Manual

Page: 97 / 566

B. Laser Control Circuit
1. Outline
Figure 2-3-2
This circuit controls the laser in response to the VIDEO signals (/VDO0 to /VDO7) from the
video controller.
The D-CPU outputs the TOP OF PAGE signal (/TOP), which is generated based on the ITB
HOME POSITION DETECTION signal (/ITBHP), to the video controller in a specified period of
time after receiving the PRINT signal (/PRNT). (See page 2-56 for ITB home position detection.)
The video controller sets the VIDEO DATA ENABLE signal (/VDOEN) “L” in a specified period of
time after the /TOP signal is input and sends the /VDO signal of an image to the DC controller.
The /VDO signal sent from the video controller is input to the line memory (IC1005) on the DC
controller PCB. This line memory is a buffer that holds a line of data. The video data written
into the line memory is read with the PRINTER CLOCK signal (PCLK) synchronized by the BD
INPUT signal (/BDIN) and sent to the gate array (IC1003). The gate array generates the VIDEO
DATA signals (VOUT0 to 7) based on the /VDO signal and UNBLANKING signal (/UNBLK:
LASER EMISSION signal to detect /BD signal in the non-image area) and sends them to the
laser driver PCB.
The VIDEO DATA signals sent to the laser driver PCB is pulse-width-modulated (laser-ON
time is changed according to the /VDO signal sent from the video controller) in the PWM IC
(IC1101) and sent to the laser drive IC (IC1102) as LASER DRIVE signal (/VDATA). The laser
diode (LD) is turned ON/OFF according to the /VDATA signal at a constant intensity.
The laser drive IC turns ON the laser diode according to the /VDATA signal when the LASER
EMISSION ENABLE signal (/LSEBN) is “L.”
This circuit contains the laser current monitor circuit, which has a function to measure the
laser current value, in order to prevent image defect caused by deterioration of the laser diode.
During image formation, the switching circuit turns ON/OFF the laser with /VDATA signal.
2 - 39
CHAPTER 2
PWM
circuit
R1117
R1118
Gate
array
(IC1003)
DC controller PCB
PD
LD
D-CPU
(IC1001)
/VDO0~7
Laser driver IC
(IC1102)
BD PCB
/BDI
/TOP
/LSYNC
Laser driver PCB
/PRNT
VOUT0~7
Line
memory
(IC1005)
PWM IC
(IC1101)
PCLK
LON
/LSENB
/VDATA
Laser current
monitor circuit
ILM
LASER5V
RO
/DTOP
+5V
BD synch-
ronizing IC
(IC1006)
PCLK
C1122
VCLK
/VDOEN
Switching circuit
Constant
current
circuit
LD
PD
LON
/LSENB
PCLK
M-CPU
(IC1009)
/DTOPE
/ITBHP
/BDO
Current
/voltage
conversion
circuit