Canon LBP-2000, Service Manual

Page: 70 / 222

2 - 31
CHAPTER 2
B . Laser Control Circuit
1 . O u t l i n e
Logic
circuit
Power
adjust
ment
circuit
Drive
circuit
J907
-8
Control
amplification
circuit
/ENBLO
/LONO
-5
/DPICH -2
LD
(laser
diode)
DC controller PCB Laser unit
Laser driver IC
PD
(photodiode)
ASIC
CPU
BD PCB
J102
-1
-3
-4
/BDIN
-10
J908
-2
-5/-8
-6
-7
-1/-4
/PRNT J104-20
/BDO J104-30
/VDO J104-31
/VDO
-7
-6
-2
-3
Receiver
VDO
/VDOUT
VDO J104-32
+5V
Figure 2-3-2
The laser control circuit operates in response to the video signals (/VDO, VDO) from the video
controller to turn on/off the laser diode (LD) at a specific intensity.
The /VDO and VDO signals from the video controller are low-amplification differential signals
with suppressed radiating noise, and they are sent to the receiver in the laser unit as they are. The
receiver serves to demodulate the low-voltage differential signals and to forward them to the logic
circuit of the laser driver IC in the form of the video out signal (/VDOUT).
When the image formation enable signal (/ENBLO) from the ASIC is ‘L’, the laser unit turns on/off
the laser diode in keeping with the /VDOUT signal.