Controlling The Laser Activation Timing; Laser On/Off Control; Horizontal Sync Control - Canon LBP3250 Series Service Manual

Chapter 2

2.3.2 Controlling the Laser Activation Timing

2.3.2.1 Laser ON/OFF Control

In this control, the laser driver turns on/off the 2 laser diodes (LD1, LD2) according to the laser control signal sent from the engine controller.
The following is the circuit diagram of the laser control.
The engine controller sends the laser control signals (CNT0, CNT1, CNT2) for changing the operation mode of the laser to the logic circuit in the laser driver IC,
as well as the video signals (VDO1, /VDO1, VDO2, /VDO2) for image formation.
The laser driver IC executes laser control according to the combination of the CNT0, CNT1, CNT2 signals.
The following is the combination of the laser control signal (CNT0, CNT1, CNT2).
Operation mode
Standby
Print
LD1 forced ON
LD2 forced ON
LD forced OFF

2.3.2.2 Horizontal Sync Control

This is the control to adjust the writing position in the image horizontal direction.
The following is the details of control procedure.
1) The engine controller controls the laser control signal during unblanking (*) to emit the laser diode (LD) forcibly.
2) The BD PCB exists on the scanning route of the laser beam, which is sent to the BD PCB.
3) The BD PCB detects this laser beam, creates BD input signal (/BDI) and sends it to the engine controller.
4) The engine controller creates horizontal sync signals (/BD) based on /BDI signal and sends the /BD signal to the main controller.
5) When /BD signal is input, the main controller outputs the video signal (VD0, /VD0) to the engine controller to adjust the writing position in image horizontal
direction.
*: Unblanking period
The period during which the laser diode is emitted in non-image area.
2-4
Engine controller PCB
IC101
+5V
CPU
J102
-13
-2 VDO1
-4
/VDO1
-8 VDO2
-10 /VDO2
IC102
-11 PDOUT
ASIC
-5 CNT0
-6
CNT1
-7
CNT2
-3/9/12
J116-2
/BDI
CNT0 CNT1 CNT2
L L L
H H H
L H L
H L L
H H L
Laser driver PCB
LD1
J11
-1
VCC
LD1
-12
switching
-10
circuit
-6
-4
Comparator
Standard voltage
-3
C16
Sample
hold circuit
-9
-8
Logic circuit
-7
-2/5/11
GND
J31-2
BD PCB
F-2-3
T-2-2
Laser control OFF
Can emit the laser according to the video signal
LD1 forcibly turned ON
LD2 forcibly turned ON
LD1, LD2 forcibly turned OFF
PD LD2
LD2
switching
circuit
Comparator
C18
Sample
hold circuit
Laser driver IC
Details
0019-9510
0019-9511