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3-16

Confidential

8 Rear side of the machine

Harness colors are subject to change for some reason.

Side thermistor

harness ASSY

(WH)

Center thermistor

harness ASSY

(WH)

LVPS-heater harness

(BK, WH)

Fuser unit heater harness (WH)

Fan harness (RD, BK, WH)

New toner sensor flat cable

HVPS flat cable

Polygon motor harness (WH)

High-voltage power supply PCB ASSY

Eject sensor PCB ASSY

Laser unit flat cable

Ground harness (GR/YW)

Registration front/rear

sensor harness

(GR, WH, BL, RD)

Default Chapter4
- Table of Contents4
Safety Information10
Chapter 1 Supplemental Specifications17
General17
Network Connectivity25
Service Information26
Supplies28
Media Specifications36
Fax (Only for the Models with Fax Function)37
Copy38
Scanner40
Chapter 2 Error Indications and Troubleshooting41
Introduction41
- Precautions41
- Checks before Commencing Troubleshooting43
Overview45
- Cross-Section Drawing45
  - Printer Part45
  - Scanner Part47
- Paper Feeding49
  - Printer Part49
  - Scanner Part51
- Operation of each Part and Location of Parts52
- Block Diagram54
- Main Components55
Error Indications57
- Error Codes58
- Error Message65
  - LCD Models65
  - Touch Panel Models74
- Communication Errors83
Troubleshooting87
- Error Cause and Remedy87
- Troubleshooting for Paper Feeding Problems113
- Troubleshooting for Image Defects123
  - Image Defect Examples123
  - Troubleshooting Image Defect124
- Troubleshooting for Software Problems138
  - Unable to Receive Data138
- Troubleshooting for Network Problems139
  - Cannot Make a Print through Network Connection139
  - Cannot Connect to Access Point139
- Troubleshooting for Control Panel Problems140
- Troubleshooting for Toner Cartridge and Drum Unit Problems141
- Troubleshooting for Fuser Unit Problems143
  - Fuser Unit Failure143
- Troubleshooting for Laser Unit Problems143
  - Laser Unit Failure143
- Troubleshooting for PCB Problems144
  - Main PCB Failure144
  - Full Memory144
- Troubleshooting for Document Feeding Problems145
- Troubleshooting for Scanning Image Defect148
- Troubleshooting for Fax/Phone Problems153
- Troubleshooting for Other Problems155
Chapter 3 Disassembly/Reassembly158
Safety Precautions158
Packing159
Screw Catalogue160
Screw Torque List161
Lubrication163
Overview of Gears164
Harness Routing166
Disassembly Flow Chart179
Disassembly Procedure180
- Preparation180
- Cord Hook182
- Back Cover183
- Outer Chute ASSY184
- Front Cover ASSY / Support Flap185
- Side Cover R188
- Fuser Cover189
- Inner Chute ASSY190
- Side Cover L / Speaker Harness ASSY / Handset Holder ASSY (for Models with Handset)191
- Document Scanner Unit194
- ADF Unit (for Models with ADF)197
  - ADF Unit197
  - ADF Cover ASSY / Document Stopper200
  - Document Sub Tray201
  - Document Separate Roller ASSY203
  - ADF Separation Holder ASSY204
  - Second Side CIS Unit / Second Side CIS Flat Cable (Only for Models with Duplex Scanning)205
- Document Cover ASSY (for Models Without ADF)210
- Panel Unit (for Touch Panel Models)212
  - Panel Unit212
  - Panel PCB ASSY / NFC PCB ASSY / LCD213
  - Touch Panel ASSY214
- Panel Unit (for Non-Touch Panel Models)215
  - Panel Unit215
  - Panel PCB ASSY216
  - Lcd217
- Panel Flat Cable / First Side CIS Unit / First Side CIS Flat Cable218
- Modem Flat Cable / Modem PCB ASSY225
- Joint Cover ASSY227
- Fuser Unit228
- Low-Voltage Power Supply PCB ASSY230
- New Toner Sensor PCB ASSY232
- HVPS Flat Cable / High-Voltage Power Supply PCB ASSY233
- Fan235
- Toner Box Relay PCB ASSY (for Models with Toner Box)236
  - MP Relay PCB ASSY (for MP Models)236
  - Toner Box New PCB ASSY (for Models with Toner Box)236
- Laser Unit Flat Cable / Laser Unit238
- Filter240
- Wireless LAN PCB (Only for Wireless Network Models)241
- Roller Holder ASSY242
- Main PCB ASSY243
- T1 Clutch / Registration Clutch244
- Frame L Unit247
- Paper Feed Motor / Paper Feed Motor Flat Cable250
- Fuser Gear 64R/36R252
- Toner Sensor PCB ASSY (Only for Models with Toner Box)253
- Front Cover Sensor254
- Eject Sensor PCB ASSY255
- Registration Front/Rear Actuator Holder ASSY257
- Paper Feed Roller ASSY / Paper Feed Sensor PCB ASSY260
Chapter 4 Adjusting and Updating Settings as Required after Parts Replacement261
If You Replace the Main Pcb Assy261
- Installing Firmware (Sub Firmware and Main Firmware)262
  - Checking Firmware Version262
  - Installing Firmware263
- Initializing the EEPROM of the Main PCB ASSY(Function Code 01)263
- Setting by Spec, Setting Serial Number and Entering Adjusted Value of Laser Unit264
- Adjusting Touch Panel (Function Code 61)(Touch Panel Models Only)266
- Acquiring White Level Data (Function Code 55)266
If You Replace the Low-Voltage Power Supply Pcb Assy267
- Reset Irregular Power Supply Detection Counter of the Low-Voltage Power Supply PCB (Function Code 88)267
If You Replace the Laser Unit268
- Entering Adjusted Value of Laser Unit269
If You Replace the Panel Unit or Panel Control Pcb271
- Adjusting Touch Panel (Function Code 61) (Touch Panel Models Only)271
- Checking LCD Operation (Function Code 12)271
If You Replace the Adf Unit, First Side Cis Unit, Second Side Cis Unit or Document Scanner Unit272
- Acquiring White Level Data (Function Code 55)272
- Scanning and Printing Check272
Chapter 5 Service Functions273
Function Code273
- How to Enter Maintenance Mode273
  - Method of Entering Maintenance Mode for Service Personnel273
  - Method of Entering End-User Accessible Maintenance Mode274
- List of Maintenance Mode Functions275
- Details of Maintenance Mode Functions276
Other Service Functions331
- Drum Cleaning331
- Print Communication Error List333
- Resetting Drum Counter334
Chapter 6 Wiring Diagram335
- Wiring Diagram335
Chapter 7 Periodical Maintenance336
Periodical Replacement Parts336
Appendix 1 Serial Numbering System337
Appendix 2 Deleting User Setting Information338
Appendix 3 Installing the Maintenance Printer Driver339

Brand	Brother
Model	MFC-B7720DN
Category	All in One Printer
Language	English

Brother MFC-B7720DN Service Manual

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