Brother MFC-9420CN Service Manual page 32

CHAPTER 3 THEORY OF OPERATION
This chapter gives an overview of the scanning and printing mechanisms as well as the sensors,
actuators, and control electronics. It aids in understanding the basic principles of operation as
well as locating defects for troubleshooting.
3.1 OVERVIEW ......................................................................................................................3-1
3.2 PRINTING MECHANISM .................................................................................................3-2
3.2.1 Print System and Transfer System ......................................................................3-7
[ 1 ] Structure of the machine ...................................................................................3-8
[ 2 ] Basic structure of the printing system................................................................3-9
[ 3 ] Details of each process ...................................................................................3-11
3.2.2 Laser ASSY PU..................................................................................................3-21
3.2.3 Paper Transportation System.............................................................................3-22
3.2.4 Fusing Unit .........................................................................................................3-23
3.3 STRUCTURE OF THE CONTROL SYSTEM ................................................................3-25
3.3.1 Basic Structure ...................................................................................................3-25
[ 1 ] Electrical system and function .........................................................................3-25
3.3.2 Control System ...................................................................................................3-32
[ 1 ] Control of the print process .............................................................................3-32
3.3.3 Main PCB (Video Controller PCB)......................................................................3-41
[ 1 ] Outline .............................................................................................................3-41
[ 2 ] Circuit...............................................................................................................3-41
3.4 SCANNER MECHANISM...............................................................................................3-45
CONTENTS
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