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Confidential

9.18 Fuser unit

(1) Release the Fuser unit heater harness from the securing fixtures, and disconnect it from

the LVPS-heater harness.

Fig. 3-64

Harness routing: Refer to “8. Rear side of the machine”.

(2) Disconnect the Center thermistor harness ASSY and the Side thermistor harness ASSY

from the Eject sensor PCB ASSY.

(3) Release the Center thermistor harness ASSY and the Side thermistor harness ASSY from

the securing fixtures.

Fig. 3-65

Harness routing: Refer to “8. Rear side of the machine”.

LVPS-heater harness

Fuser unit heater harness

Side thermistor

harness ASSY

Center thermistor

harness ASSY

Eject sensor PCB ASSY

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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