Canon LBP1760P, Service Manual

Page: 64 / 394

C. Scanner System
Figure 2-3-4 is the scanner motor control circuit.
Figure 2-3-4
The scanner motor is a three-phase, eight-pole DC brushless motor with hall elements, and is
unified with the drive circuit.
When the printer is turned ON, the CPU (IC501) on the engine controller divides the oscilla-
tion frequency of the crystal oscillator (X501) and generates standard clock.
When the /PRNT signal sent to the CPU becomes “L,” the CPU sets the SCANNER MOTOR
ACCELERATION signal (/ACC) to “L.” The scanner driver IC rotates the scanner motor when the
/ACC signal is “L” and accelerates while the /ACC signal is “L.”
While the scanner motor is rotating, the CPU forces laser emission, and the /BDI signal is
sent from the BD PCB. The CPU compares the /BDI signal cycle with the standard clock in the
frequency comparator of the CPU and controls the rotation speed of the scanner motor by con-
trolling the /ACC signal until the the scanner motor reaches the prescribed speed.
When stopping the scanner, the CPU decelerates the scanner rotation by setting the SCAN-
NER MOTOR DECELERATION signal (/DEC) to “L.”
The CPU monitors the /BDI signal sent from the BD PCB to judge whether the scanner motor
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CHAPTER 2
Engine controller PCB
BD PCB
CPU(IC501)
Oscillator
Standard
clock
Frequency
comparator
J401-1
Laser/scanner unit
Integration
circuit
M
Scanner driver IC
Scanner motor
J401-4
J53-4
J53-1
X2
90
89
64
63
6
/PRNT J53-2
P67
/BDI J551-2
J53-6
/ACC
/ACC J53-2 J401-3
/DEC
/DEC
J53-3 J401-2
X1
X501
Drive
circuit
+24VA
+24VA