Canon Laser Shot LBP-1120, Service Manual

Page: 40 / 117

2 - 21
CHAPTER 2
C. Scanner System
The scanner motor control circuit is shown below.
Figure 2-3-4
The scanner motor is a 3-phase DC brushless motor and is unified with the scanner motor drive circuit.
When the printer is turned ON, the CPU (IC201) divides the oscillation frequency of the crystal oscillator (X201),
generating the reference clock.
When a pickup command is sent from the interface controller, the CPU forcibly accelerates the scanner motor by
turning the SCANNER MOTOR ACCELERATION signal (/ACC) “L” and the SCANNER MOTOR DECELERATION
signal (/DEC) “H” for 0.2 seconds.
Then, the CPU obtains the HORIZONTAL SYNCHRONOUS INPUT signal (/BDI) from the BD sensor by emitting
the laser diode.
The frequency of the /BDI signal is in proportion to the rotation number of the scanner motor.
To rotate the scanner motor in the specified rotation number, the CPU compares the BDI signal frequency with the
reference frequency in the frequency comparator of the CPU, and controls the output of the /ACC signal and /DCC
signal.
After 1.5 seconds from the time the scanner motor reaches its specified rotation number, the CPU determines that
the scanner is ready.
The CPU determines whether or not the scanner motor is rotating in the specified rotation number by monitoring the
/BDI signal sent from the BD sensor.
When the scanner motor is rotating at the specified value, the laser beam scans onto the photosensitive drum at a
constant speed.
To stop the scanner motor, the CPU turns the /ACC signal to “H” and the /DEC signal to “L”.
Engine controller PCB
BD sensor
IC201
Oscillator
Standard
clock
Frequency
comparator
J802-4
Laser/scanner unit
Integration
circuit
Drive
circuit
M
Scanner driver IC
Scanner motor
J802-1
J208-1
J208-4
X0
4
3
55
56
/BDI J801F-2 J208F-11
/ACC
/ACC J208-3 J802-2
/DEC /DEC
J208-2 J802-3
X1
X201
CPU
+24VA
+24VA
+3.3V