Brother MFC-9420CN User manual

Confidential
FACSIMILE EQUIPMENT
SERVICE MANUAL
MODELS: MFC-9420CN

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PREFACE
This Service Manual is intended for use by service personnel and details the specifications,
construction, theory of operation, and maintenance for the Brother machines noted on the front
cover. It includes information required for troubleshooting and service--disassembly, reassembly,
and lubrication--so that service personnel will be able to understand equipment function, repair the
equipment in a timely manner and order spare parts as necessary.
To perform appropriate maintenance so that the machine is always in the best possible condition
for the customer, service personnel must adequately understand and apply this manual.
HOW THIS MANUAL IS ORGANIZED
This manual is made up of nine chapters and appendices.
CHAPTER 1 PARTS NAMES AND FUNCTIONS
Contains external views and names of components and describes their functions. Information
about the keys on the control panel is included to help you check operation or make adjustments.
CHAPTER 2 SPECIFICATIONS
Lists the specifications of each model, which enables you to make a comparison of different
models.
CHAPTER 3 THEORY OF OPERATION
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.
CHAPTER 4 TRANSFER OF DATA LEFT IN THE MACHINE TO BE SENT FOR REPAIR
Describes how to transfer data left in the machine to be sent for repair. The service personnel
should instruct end users to follow the transfer procedure given in this chapter if the machine at the
user site cannot print received data due to the printing mechanism defective. End users can
transfer received data to another machine to prevent data loss.
CHAPTER 5 DISASSEMBLY/REASSEMBLY AND LUBRICATION
Details procedures for disassembling and reassembling the machine together with related notes.
The disassembly order flow provided enables you to see at a glance the quickest way to get to
component(s) involved.
At the start of a disassembly job, you check a disassembly order flow that guides you through a
shortcut to the object components.
This chapter also covers screw tightening torques and lubrication points to which the specified
lubricants should be applied during reassembly jobs.
CHAPTER 6 ADJUSTMENTS AND UPDATING OF SETTINGS REQUIRED AFTER PARTS
REPLACEMENT
Details adjustments and updating of settings, which are required if the head/carriage unit, main
PCB and some other parts have been replaced.
CHAPTER 7 CLEANING
Provides cleaning procedures not covered by the User's Manual. Before starting any repair work,
clean the machine as it may solve the problem concerned.

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CHAPTER 8 MAINTENANCE MODE
Describes the maintenance mode which is exclusively designed for the purpose of checks, settings
and adjustments using the keys on the control panel.
In the maintenance mode, you can update memory (EEPROM: electrically erasable programmable
read-only memory) contents for optimizing the drive conditions of the head/carriage unit, paper
feed roller or paper ejection roller (if they have been replaced) or for setting the CIS scanner area,
for example. You can also customize the EEPROM according to the shipment destination of the
machine concerned. In addition, you can perform operational checks of the LCD, control panel
PCB or sensors, perform a print test, display the log information or error codes, and modify
firmware switches (WSW).
CHAPTER 9 ERROR INDICATION AND TROUBLESHOOTING
Details error messages and codes that the incorporated self-diagnostic functions display if any
error or malfunction occurs. If any error message appears, refer to this chapter to find which
components should be checked or replaced.
The latter half of this chapter provides sample problems that could occur in the main sections of
the machine and related troubleshooting procedures. This will help service personnel pinpoint and
repair defective components.
APPENDIX 1 SERIAL NUMBERING SYSTEM
Shows the location of serial number labels put on some parts and lists the coding information
pertaining to the serial numbers.
APPENDIX 2 FIRMWARE INSTALLATION
Provides instructions on how to update firmware stored in the flash ROM on the main PCB or load
firmware to a new main PCB from the host PC.
No hardware replacement is required for updating.
APPENDIX 3 CUSTOMIZING CODES ACCORDING TO SHIPPING DESTINATION
Lists the customizing codes for the various preferences exclusively designed for each destination
(e.g. language). Those codes are stored in the memory (EEPROM) mounted on the main PCB. If
the main PCB is replaced with a new one, therefore, you will need to set the proper customizing
codes with the machine in the maintenance mode.
APPENDIX 4 FIRMWARE SWITCHES (WSW)
Describes the functions of the firmware switches, which can be divided into two groups: one is for
customizing preferences designed for the shipping destination (as described in Appendix 3) and
the other is for modifying preferences that match the machine to the environmental conditions.
Use the latter group if the machine malfunctions due to mismatching.
APPENDIX 5 WIRING DIAGRAM
Provides the wiring diagram that helps you understand the connections between PCBs.
APPENDIX 6 CIRCUIT DIAGRAMS
Provides the circuit diagrams of the NCU PCB and power supply PCB.
APPENDIX 7 VIEWING THE EVENT LOG FILE
When installing the printer driver, the installer logs events that occur during the installation
process in the event log file. This appendix views a sample of the event log file. Selecting Start |
Program | Brother | MFL-Pro Suite model name | Installation Diagnostics reads out the event log
file.
This manual describes the models and their versions destined for major countries.
The specifications and functions are subject to change depending upon each destination.

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TABLE OF CONTENTS
CHAPTER 1 PARTS NAMES & FUNCTIONS
1.1 EQUIPMENT OUTLINE.............................................................................................1-1
1.2 CONTROL PANEL....................................................................................................1-2
1.3 COMPONENTS.........................................................................................................1-4
CHAPTER 2 SPECIFICATIONS
2.1 GENERAL..................................................................................................................2-1
2.1.1 General Specifications .........................................................................................2-1
2.1.2 Paper Specifications.............................................................................................2-2
2.1.3 Printable Area ................................................................................................................2-3
2.2 SPECIFICATIONS LIST ............................................................................................2-4
CHAPTER 3 THEORY OF OPERATION
3.1 OVERVIEW................................................................................................................3-1
3.2 PRINTER SECTION..................................................................................................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

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CHAPTER 4 TRANSFER OF DATA LEFT IN THE MACHINE TO BE SENT FOR REPAIR
4.1 TRANSFERRING RECEIVED FAX DATA................................................................4-1
CHAPTER 5 DISASSEMBLY/REASSEMBLY AND LUBRICATION
5.1 DISASSEMBLY/REASSEMBLY ...............................................................................5-1
Safety Precautions........................................................................................................5-1
Tightening Torque.........................................................................................................5-2
Preparation ...................................................................................................................5-3
How to Access the Object Component.........................................................................5-3
Disassembly Flowchart.................................................................................................5-4
5.1.1 AC Cord................................................................................................................5-5
5.1.2 OPC Belt Cartridge...............................................................................................5-6
5.1.3 Paper Tray............................................................................................................5-6
5.1.4 Fusing Unit...........................................................................................................5-7
5.1.5 Side Cover LR....................................................................................................5-11
5.1.6 Top Side L..........................................................................................................5-12
5.1.7 ADF Unit.............................................................................................................5-13
5.1.8 Scanner Unit.......................................................................................................5-28
5.1.9 Pull Arm/Scanner Slider L, R..............................................................................5-29
5.1.10 IS Lock Lever ASSY...........................................................................................5-30
5.1.11 Tray (TP)............................................................................................................5-30
5.1.12 Panel..................................................................................................................5-31
5.1.13 Battery ASSY......................................................................................................5-35
5.1.14 Main PCB...........................................................................................................5-36
5.1.15 NCU PCB ASSY.................................................................................................5-37
5.1.16 Top Side R .........................................................................................................5-38
5.1.17 Cleaning Roller Cover PU / Cleaning Roller PU.................................................5-38
5.1.18 Top Cover...........................................................................................................5-39
5.1.19 Center Cover......................................................................................................5-40
5.1.20 Right Side Cover PU..........................................................................................5-40
5.1.21 Side Cover LF ....................................................................................................5-41
5.1.22 Interlock Switch PU (Front) ................................................................................5-41

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5.1.23 Waste Toner Auger PU......................................................................................5-42
5.1.24 Waste Toner Agitator PU...................................................................................5-42
5.1.25 Erase Lamp PU..................................................................................................5-43
5.1.26 Marker Sensor....................................................................................................5-44
5.1.27 Toner Density Sensor PU...................................................................................5-44
5.1.28 Cleaning Roller Clutch PU..................................................................................5-45
5.1.29 Main Motor PU ...................................................................................................5-45
5.1.30 Fuser Clutch PU.................................................................................................5-46
5.1.31 TR Cam Clutch...................................................................................................5-47
5.1.32 Registration Clutch PU.......................................................................................5-47
5.1.33 Paper Feed Clutch PU .......................................................................................5-48
5.1.34 Developer Motor PU...........................................................................................5-48
5.1.35 Waste Toner Holder ASSY PU ..........................................................................5-49
5.1.36 Developer Clutch PU (DCLY/DCLM/DCLC/DCLK)............................................5-49
5.1.37 Developer Gear PU / Developer Drive ASSY PU...............................................5-50
5.1.38 OPC Drive Gear ASSY PU.................................................................................5-50
5.1.39 Main Drive Gear ASSY PU.................................................................................5-51
5.1.40 Waste Toner Feeder PU....................................................................................5-52
5.1.41 Toner Sensor PU (TPD).....................................................................................5-53
5.1.42 Right Toner Guide PU........................................................................................5-54
5.1.43 Laser ASSY PU / Laser Unit Fan ASSY PU.......................................................5-54
5.1.44 Inner Front Cover PU / Front Cover PU.............................................................5-56
5.1.45 Right Tray Guide PU..........................................................................................5-56
5.1.46 Engine Control Board PU...................................................................................5-57
5.1.47 Power Supply Fan PU / Interlock Switch PU (Top, Paper Exit) /
Power Supply Fan Duct PU...............................................................................5-58
5.1.48 Speaker..............................................................................................................5-59
5.1.49 Scanner Door Sensor.........................................................................................5-59
5.1.50 HV Power Supply PU .........................................................................................5-60
5.1.51 LV Power Supply PU / Power Supply Bracket PU ASSY...................................5-61
5.1.52 Fuser Connector PU...........................................................................................5-62
5.1.53 Toner Retract Solenoid PU (DESLY/DESLM/DESLC/DESLK) /
Toner Retract Cam PU.......................................................................................5-63

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5.1.54 Toner Sensor PU (TTR).....................................................................................5-64
5.1.55 Toner Present Sensor PU..................................................................................5-65
5.1.56 Belt Sensor.........................................................................................................5-65
5.1.57 Left Tray Guide PU / Paper Size Sensor PU / Room Temp Thermistor PU ......5-66
5.1.58 Left Toner Guide PU ..........................................................................................5-67
5.1.59 Paper Exit Unit ...................................................................................................5-68
5.1.60 Transfer Roller ASSY PU...................................................................................5-69
5.1.61 Transfer Base ASSY PU....................................................................................5-69
5.1.62 Registration Roller ASSY PU .............................................................................5-70
5.1.63 Registration Actuator PU....................................................................................5-70
5.1.64 Exit Guide ASSY PU / Exit Drive ASSY PU / Exit Idle Roller ASSY PU.............5-71
5.1.65 Paper Sensor (PFUL).........................................................................................5-72
5.1.66 Exit Roller ASSY PU / Paper Exit Actuator PU ..................................................5-73
5.1.67 Fuser Exit Actuator PU.......................................................................................5-74
5.1.68 Paper Sensor (PT2) ...........................................................................................5-74
5.1.69 Discharging Brush PU........................................................................................5-75
5.1.70 Back Cover Latch ASSY PU...............................................................................5-76
5.1.71 Transfer Roller Guide PU...................................................................................5-77
5.1.72 Paper Guide (A) PU ...........................................................................................5-78
5.1.73 Paper Guide (B) PU ...........................................................................................5-78
5.1.74 Paper Guide (C) PU / Paper Sensor (PT1, PEU) / OHP Sensor PU /
Tray Empty Actuator PU....................................................................................5-79
5.1.75 Paper Guide (D) PU...........................................................................................5-80
5.1.76 Paper Feed Roller / Separator Pad....................................................................5-80
5.2 LUBRICATION ........................................................................................................5-81
5.3 HARNESS ROUTING..............................................................................................5-82
CHAPTER 6 ADJUSTMENTS AND UPDATING OF SETTINGS, REQUIRED AFTER PARTS
REPLACEMENT
6.1 IF YOU REPLACE THE MAIN PCB..........................................................................6-1
6.1.1 EEPROM Customizing.........................................................................................6-1
6.1.2 EEPROM Parameter Initialization........................................................................6-1
6.1.3 ID Code Entry to the EEPROM............................................................................6-1

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6.1.4 CIS Scanner Area Setting....................................................................................6-2
6.1.5 Setting Which Allows the User to Select the Country...........................................6-2
6.2 IF YOU REPLACE THE ENGINE CONTROL BOARD PU.......................................6-4
6.3 ADJUSTMENT OF THE GUIDE B POSITION OF TOP FUSE COVER FU.............6-5
6.4 PERIODIC MAINTENANCE PROCEDURES............................................................6-6
6.4.1 Replacement of OPC Belt Cartridge ....................................................................6-6
6.4.2 Replacement of Fusing Unit...............................................................................6-10
6.4.3 Replacement of Transfer Roller ASSY PU (120K KIT)......................................6-13
6.4.4 Replacement of Cleaning Roller PU (120K KIT)................................................6-15
6.4.5 Replacement of Paper Feed Roller and Separator Pad (120K KIT)..................6-17
6.4.6 Replacement of Transfer Unit PU (120K KIT)....................................................6-23
6.5 IF YOU REPLACE THE OPC BELT CARTRIDGE.................................................6-25
6.6 IF YOU REPLACE THE FUSING UNIT...................................................................6-26
CHAPTER 7 CLEANING
CHAPTER 8 MAINTENANCE MODE
8.1 MAINTENANCE MODE FOR THE MACHINE..........................................................8-1
8.1.1 Entry into the Maintenance Mode.........................................................................8-1
8.1.2 List of Maintenance Mode Functions....................................................................8-2
8.1.3 User-access to the Maintenance Mode................................................................8-3
8.1.4 Detailed Descriptions of Maintenance Mode Functions.......................................8-4
8.1.4.1 EEPROM Parameter Initialization (Function mode 01/91)...........................8-4
8.1.4.2 Printout of Scanning Compensation Data (Function mode 05)....................8-5
8.1.4.3 Placement of CIS Unit in Position for Transportation (Function mode 06) ..8-7
8.1.4.4 ADF Performance Test (Function mode 08)................................................8-7
8.1.4.5 Test Pattern 1 (Function mode 09)..............................................................8-8
8.1.4.6 Firmware Switch Setting and Printout..........................................................8-9
[1] Firmware switch setting (Function mode 10) ...................................................8-9
[2] Printout of firmware switch data (Function mode 11).....................................8-11
8.1.4.7 Operation Check of LCD (Function mode 12) ...........................................8-12
8.1.4.8 Operational Check of Control Panel PCB (Function mode 13)..................8-13

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8.1.4.9 Sensor Operational Check (Function mode 32).........................................8-14
8.1.4.10 EEPROM Customizing (Entering of the country code for Europe/Oceania.)
(Function mode 52)....................................................................................8-15
8.1.4.11 Received Data Transfer Function (Function mode 53)..............................8-16
8.1.4.12 Fine Adjustment of Scan Start/End Positions (Function mode 54)............8-18
8.1.4.13 Acquisition of White Level Data and CIS Scanner Area Setting
(Function mode 55)....................................................................................8-20
8.1.4.14 Paper Feeding and Ejecting Test (Function mode 67) ..............................8-20
8.1.4.15 EEPROM Customizing (Direct entering of the four-digit code.)
(Function mode 74)....................................................................................8-21
8.1.4.16 Display of the Equipment’s Log Information (Function mode 80)..............8-22
8.1.4.17 Machine Error Code Indication (Function mode 82)..................................8-25
8.1.4.18 Output of Transmission Log to the Telephone Line (Function mode 87)...8-25
8.1.4.19 Cancellation of the Memory Security Mode
(Not applicable to the Japanese model) ....................................................8-25
8.1.4.20 Hex Dump Mode........................................................................................8-26
8.1.4.21 Indication of the Firmware Version ............................................................8-26
8.2 ENGINE SERVICE MODE.......................................................................................8-27
8.2.1 Entry into the Engine Service Mode...................................................................8-27
8.2.2 List of Engine Service Mode Functions..............................................................8-28
8.2.3 Detailed Descriptions of Engine Service Mode Functions..................................8-29
8.2.3.1 Test Print (Code 31)...................................................................................8-29
8.2.3.2 Next Care Information (Code 32)...............................................................8-32
8.2.3.3 Tray Type (Code 33)..................................................................................8-35
8.2.3.4 Total Page (Code 34).................................................................................8-35
8.2.3.5 Each Image (Code 35)...............................................................................8-36
8.2.3.6 Clear Care (Code 36).................................................................................8-37
8.2.3.7 Media Manage (Code 37) ..........................................................................8-37
8.2.3.8 Extend Media (Code 38)............................................................................8-38
8.2.3.9 Factory Mode (Code 39)............................................................................8-38
[ 1 ] Margin Adjust (Code 43)............................................................................8-39
[ 2 ] Life Period Set (Code 44) ..........................................................................8-40
[ 3 ] NVRAM Tune Up (Code 45)......................................................................8-41

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[ 4 ] NVRAM Initial (Code 46)............................................................................8-45
[ 5 ] Total Page Set (Code 47)..........................................................................8-45
[ 6 ] Each Image Set (Code 48) ........................................................................8-46
[ 7 ] Next Life Set (Code 49) .............................................................................8-47
CHAPTER 9 ERROR INDICATION AND TROUBLESHOOTING
9.1 ERROR INDICATION................................................................................................9-1
9.1.1 Equipment Errors .................................................................................................9-1
[ 1 ] Error messages appearing on the LCD .......................................................9-1
[ 2 ] Error codes shown in "MACHINE ERROR X X" messages.........................9-5
9.1.2 Communications Errors......................................................................................9-15
9.2 TROUBLESHOOTING ............................................................................................9-19
9.2.1 Introduction.........................................................................................................9-19
9.2.2 Precautions ........................................................................................................9-19
9.2.3 Checking Prior to Troubleshooting.....................................................................9-19
9.2.4 Troubleshooting Based on Problem Type..........................................................9-20
[ 1 ] Software setting problems .........................................................................9-20
[ 2 ] Image failure ..............................................................................................9-23
[ 3 ] Paper transport error..................................................................................9-50
[ 4 ] Incorrect printout........................................................................................9-52
[ 5 ] Network problem........................................................................................9-54
[ 6 ] Troubleshooting of the control panel..........................................................9-58
[ 7 ] Troubleshooting of fax functions................................................................9-60
APPENDIX 1 SERIAL NUMBERING SYSTEM
APPENDIX 2 FIRMWARE INSTALLATION
A2.1 INSTALLING THE UPDATE DATA TO THE MACHINE..................................APP. 2-1
A2.2 SETTING ID CODES TO MACHINES..............................................................APP. 2-8
APPENDIX 3 CUSTOMIZING CODES ACCORDING TO SHIPPING DESTINATION
APPENDIX 4 FIRMWARE SWITCHES (WSW)

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APPENDIX 5 WIRING DIAGRAM
APPENDIX 6 CIRCUIT DIAGRAMS
NCU PCB (U.S.A. model)
NCU PCB (Europe, Oceania, Asia model)
NCU PCB (Japanese model)
POWER SUPPLY PCB 100V, 127V
POWER SUPPLY PCB 240V
APPENDIX 7 VIEWING THE EVENT LOG FILE

FACSIMILE EQUIPMENT
PARTS REFERENCE LIST
MODEL: MFC9420CN

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