C. Scanner System - Canon LBP-800 Service Manual

CHAPTER 2

C. Scanner System

The scanner motor control circuit is shown below.
Engine controller PCB
CPU
/ACC
Frequency
comparator
/DEC
Standard
clock
X1
Oscillator
X0
IC201
The scanner motor is a 3-phase brushless motor with built in hall element and is in a unit
with the scanner motor drive circuit.
When the printer is turned ON, the CPU (IC201) divides the oscillation frequency of the crys-
tal oscillator (X201) and generates the reference clock.
When a pick-up command is sent from the interface controller, the CPU forces the scanner
to accelerate by turning the SCANNER MOTOR ACCELERATION signal (/ACC) to "L" and the
SCANNER MOTOR DECELERATION signal (/DEC) to "H" for 0.2 seconds.
The CPU makes the laser diode emit the laser to obtain the HORIZONTAL SYNC INPUT sig-
nal (/BDI) form the BD sensor in proportion to the number of the scanner motor rotation.
Then the CPU compares the /BDI signal frequency with the reference frequency with a fre-
quency comparator in the CPU. In order to generate the specified number of the scanner motor
rotation, the CPU controls the rotation by outputting the /ACC signal and the /DEC signal. In
1.5 seconds after the number of the scanner motor rotation reaches the specified value, the
scanner becomes ready.
The CPU monitors the /BDI signal sent from the BD PCB to determine whether the scanner
motor is rotating at the specified value of the rotation.
When the scanner motor is rotating at the specified value, the laser beam reflected from the
four-faced mirror scans onto the photosensitive drum at a constant speed.
In order to stop the scanner motor, the CPU turns the /ACC signal to "H", and the /DEC sig-
nal to "L".
2 - 20
+3.3V
/BDI
J208F-11
+24VA
J208-4
J208-3 /ACC
4
J208-2
/DEC
3
J208-1
55
X201
56
Figure 2-3-4
Laser/scanner unit
J801F-2
BD sensor
+24VA
J802-1
Scanner driver IC
J802-2
Integration
circuit
J802-3
J802-4
Scanner motor
Drive
circuit
M