Canon LBP 2460 Service Manual - Page 73

B.

Laser Control Circuit

1.

Outline

Figure 2-3-2

This circuit switches the laser diode (LD) ON and OFF at a constant intensity in response to the

VDO signal sent from the video controller.

The VDO signal sent from the video controller to the DC controller is sent as is, to the

switching circuit in the laser driver circuit.

The microprocessor (CPU: IC201) outputs the INTENSITY CONTROL signals (APC1,

APC2) from DA output ports to the analog adder circuit according to the internal data.

The

output from analog adder circuit is sent to the laser current setting circuit in the laser driver as the

LASER OUTPUT signal (LLCONT).

This analog adder circuit performs weighted addition for the APC1 signal and APC2 signal at

a ratio of approximately 8:1.

The CPU adjusts the value of the LLCONT signal by changing the

APC1 signal for rough adjustment and APC2 signal for fine adjustment.

The output current of the laser current setting circuit is sent to the switching circuit and the

laser diode is switched ON and OFF in response to the VDO signal when the VIDEO DATA

ENABLE signal (/LENBL) (described later) is “L”.

2.

Automatic laser emisison control

The CPU on the DC controller controls the intensity of the laser beam according to the APC1

signal (laser beam intensity rough adjustment signal) and APC2 signal (laser beam intensity fine

adjustment signal).

The analog adder circuit adds the APC1 and APC2 signals, generates a

LASER OUTPUT signal (LLCONT), and outputs it to the laser current setting circuit in the laser

driver.

The CPU performs the automatic laser power control (APC) to let the laser diode emit

constant light, then adjusts the LLCONT signal.

This control is divided into initial APC and between-page APC.

CHAPTER 2

2 - 27

AMP

PD

LD

IC201

APC1

APC2

Analog

adder

circuit

/LENBL

J202-4

J1001-6

IC205

Gate

array

/BD

VDO

/PRNT

PD

J202-3

J1001-7

J201-C6

J201-C16

J201-C1

CPU

LLCONT

J202-2

J1001-8

VDO

J202-7

J1001-3

/LON

J202-5

J1001-5

/BDI

J206-2

J6-2

/RD

/WR

DATA

ADBUS

Switching

circuit

Vcc

DC controller PCB

Laser current

setting circuit

Laser driver PCB

(Photo diode)

(Laser diode)

BD PCB

Logic IC

Section	Page
PREFACE	5
CONTENTS	7
CHAPTER 1	11
I. FEATURES	13
II. SPECIFICATIONS	15
III. SAFETY INFORMATION	19
IV. PARTS OF THE PRINTER	20
V. INSTALLATION	26
VI. MAINTENANCE AND SERVICING BY THE CUSTOMER	35
VII. OPERATION	37
CHAPTER 2	45
I. BASIC OPERATION	47
II. ENGINE CONTROL SYSTEM	50
III. LASER/SCANNER SYSTEM	72
IV. IMAGE FORMATION SYSTEM	78
V. PICK-UP/FEED SYSTEM	88
VI. OVERALL CONTROL SYSTEM	106
VII. OPTION CONTROL SYSTEM	110
VIII. ENVELOPE FEEDER	113
IX. DUPLEXING UNIT	117
X. PAPER DECK	127
CHAPTER 3	141
I. EXTERNALS	143
II. DRIVE SYSTEM	152
III. PAPER TRANSPORT SYSTEM	154
IV. EXPOSURE SYSTEM	163
V. ELECTROSTATIC IMAGING/DEVELOPING/CLEANING SYSTEM	164
VI. FIXING SYSTEM	166
VII. ELECTRONIC COMPONENTS	174
VIII. ENVELOPE FEEDER	181
IX. DUPLEXING UNIT	187
X. OPTION CONTROLLER	194
XI. PAPERDECK	195
CHAPTER 4	213
I. MAINTENANCE AND SERVICING	215
II. TOOLS	219
III. MEASUREMENT AND ADJUSTMENT	228
IV. INITIAL CHECK	232
V. IMAGE DEFECTS	233
VI. MALFUNCTION TROUBLESHOOTING	242
VII. PAPER FEEDING TROUBLESHOOTING	265
VIII. LOCATION OF ELECTRICAL PARTS/FUNCTION	272
IX.VARIABLE RESISTORS, LEDS, TEST PINS, JUMPERS, AND SWITCHES ON PC BOARDS	287
X. LIST OF LUBRICANTS, CLEANERS	296
APPENDIX	297
I. GENERAL TIMING CHART-1/2	299
GENERAL TIMING CHART-2/2	300
II. GENERAL CIRCUIT DIAGRAM-1/3	301
GENERAL CIRCUIT DIAGRAM-2/3	302
GENERAL CIRCUIT DIAGRAM-3/3	303

Canon LBP 2460 Service Manual - Page 73

Laser Control Circuit, Outline, Automatic laser emisison control

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