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(6) Remove the screw cup M3x8 (black) screw and two taptite bind B M4x12 screws.

Remove the low-voltage power supply PCB ASSY, and disconnect the low-voltage

power supply harness from the low-voltage power supply PCB ASSY.

Fig. 3-84

Fig. 3-85

Assembling Note:

• When attaching the low-voltage power supply PCB ASSY, engage the notch on the

low-voltage power supply PCB ASSY with the hook.

• Check that the heater harness is housed in the frame L as shown in the figure below.

Otherwise the harness may be caught in some sections of the machine, and may catch

fire.

Notch

Screw cup M3×8 (black)

Taptite bind B M4x12

Low-voltage power

supply PCB ASSY

Low-voltage power supply harness

Hook

Notch

Hook

Heater harness

Heater harness is

housed in frame L

Default Chapter1
- Service Manual1
- Open Source Licensing Remarks3
- Other Information3
- Table of Contents4
Safety Information11
- Additional Information17
Chapter 1 Supplemental Specifications19
General19
Network Connectivity27
Service Information28
Supplies30
Media Specifications33
Fax (Only for the Models with Fax Function)33
Copy34
Scanner35
Chapter 2 Error Indications & Troubleshooting36
Introduction36
- Precautions36
- Checks before Commencing Troubleshooting37
Overview39
- Cross-Section Drawing39
  - Printer Part39
  - Scanner Part40
- Paper Feeding41
  - Printer Part41
  - Scanner Part42
- Operation of each Part43
- Block Diagram45
- Main Components46
Error Indications47
- Error Codes48
- Error Messages57
- Communication Errors69
Troubleshooting73
- Error Cause and Remedy73
- Troubleshooting for Paper Feeding Problems117
- Troubleshooting for Image Defects130
  - Image Defect Examples130
  - Troubleshooting According to Image Defect131
- Troubleshooting for Software Problems143
  - Cannot Receive Data143
- Troubleshooting for Network Problems144
  - Cannot Print Via Network Connection144
  - Cannot Connect to Access Point144
- Troubleshooting for Control Panel Problems144
- Troubleshooting for Toner and Drum Problems146
- Troubleshooting for Fuser Unit Problems148
  - Fuser Unit Failure148
- Troubleshooting for Laser Unit Problems148
  - Laser Unit Failure148
- Troubleshooting for PCB Problems149
  - Main PCB Failure149
  - Memory Full149
- Troubleshooting for Document Feeding Problems150
- Troubleshooting for Image Defects153
  - Defect Examples153
  - Troubleshooting According to Image Defect153
- Troubleshooting for Fax Problems157
- Troubleshooting for Other Problems159
Chapter 3 Disassembly/Reassembly161
Safety Precautions161
Packing162
Screw Catalogue163
Screw Torque List164
Lubrication167
Overview of Gears169
Harness Routing171
Disassembly Flow Chart184
- Machine184
Disassembly Procedure187
- Preparation187
- Paper Tray188
- Back Cover / Outer Chute190
- Fuser Cover191
- Fuser Unit192
- MP Cover ASSY195
- Front Cover ASSY197
- Side Cover L198
- Side Cover R199
- Adf/Document Scanner Unit200
- ADF Unit203
  - Hinge L ASSY, Hinge R, Hinge R Support, Hinge Arm R205
  - ADF Cover ASSY, Document Stopper206
  - Gear Cover, ADF Front Cover, Document Sub Tray207
  - Document Separate Roller ASSY209
  - ADF Separation Holder ASSY210
  - Second Side CIS Unit, Second Side CIS Flat Cable (Models with Duplex Printing Only)211
- Panel Unit216
  - Panel PCB ASSY, LCD (for LCD: 4.85 Inch Models)218
  - LCD Relay Flat Cable (for LCD: 3.7 Inch Models)220
  - Panel PCB ASSY, LCD, LCD Relay PCB ASSY LCD Relay Flat Cable (for LCD: 3.7 Inch Models)220
  - Touch Panel ASSY222
  - NFC PCB ASSY (Models with NFC Only)223
- USB Host PCB ASSY224
- First Side CIS Unit, First Side CIS Flat Cable225
- Joint Cover ASSY232
- Modem PCB ASSY (Models with FAX Only)234
- Stack Sensor PCB ASSY (Models with USB Host on the Rear Side Only)236
- Main PCB ASSY / Wireless LAN PCB (Wireless LAN Models Only)237
- External Temperature/Humidity Sensor239
- Laser Unit240
- PF Roller Holder ASSY242
- Low-Voltage Power Supply PCB ASSY243
- Toner Amount Detection Sensor PCB ASSY (Light Emission)246
- Main Fan248
- Filter250
- Relay Front PCB ASSY251
- Registration Clutch / T1 Pickup Clutch252
- Main Frame L ASSY253
- Paper Feed Motor256
- Develop Joint Gear 37 / Develop Joint258
- Toner Amount Detection Sensor PCB ASSY (Light Reception)259
- MP Solenoid260
- Develop Clutch 51R261
- Internal Temperature Sensor262
- Fuser Drive Gear 39263
- Eject Motor265
- Back Cover/Duplex Tray Sensor266
- LT/TT Connector267
- High-Voltage Power Supply PCB ASSY268
- Eject Sensor PCB ASSY271
- MP Roller Holder ASSY / MP Separation Pad ASSY / MP Separation Pad Spring272
- T1 Paper Feed Sensor PCB ASSY / T1 Paper Feed Actuator / T1 Paper Feed Actuator Spring273
- MP Paper Empty Sensor PCB ASSY / MP Paper Empty Actuator 1 / MP Paper Empty Actuator 2275
- Paper Empty Sensor PCB ASSY (Models with USB Host on the Rear Side Only)278
- Registration Front/Rear Sensor PCB ASSY279
Disassembly Procedure (Lt Unit)282
- Paper Tray282
- LT Roller Holder ASSY284
- LT Side Cover L285
- LT Side Cover R286
- LT Front Cover ASSY287
- LT Control PCB ASSY288
- LT Pickup Clutch289
- LT Release Clutch290
- LT Connector ASSY / LT Connector Upper293
- LT Paper Feed Sensor PCB ASSY294
- LT Paper Empty Sensor PCB ASSY297
Chapter 4 Adjusting and Updating Settings as Required after Parts Replacement298
If You Replace the Main Pcb Assy298
- Installing Firmware (Sub Firmware and Main Firmware)299
  - Checking Firmware Version299
  - Installing Firmware300
- Adjusting Touch Panel (Function Code: 61)302
- Initializing the EEPROM of the Main PCB ASSY (Function Code: 01)302
- Configure for Country/Region and Model (Function Code: 74)302
- Activating Memory Writing302
- Setting Serial Number and Entering Adjusted Value of Laser Unit303
- Acquiring White Level Data (Function Code: 55)304
- Adjusting Left-End and Upper-End Print Position (Function Code: 45) (TT Only)304
- Resetting to Factory Shipping State304
If You Replace the Low-Voltage Power Supply Pcb Assy305
- Resetting Irregular Power Supply Counter of the Low-Voltage Power Supply PCB (Function Code: 88)305
If You Replace the Laser Unit306
- Entering Adjusted Value of Laser Unit307
- Resetting Printed Pages Counter of the Laser Unit307
If You Replace the Lcd Panel Assy or Panel Pcb308
- Adjusting Touch Panel (Function Code: 61)308
- Checking LCD Operation (Function Code: 12)308
If You Replace the Adf Unit, First Side Cis Unit, Second Side Cis Unit or Document Scanner Unit309
- Acquiring White Level Data (Function Code: 55)309
- Scanning and Printing Check309
If You Replace the Fuser Unit310
- Resetting Printed Pages Counter of the Fuser Unit310
If You Replace a Pf Kit311
- Resetting Printed Pages Counter of a PF Kit311
If You Replace the Tt / Lt312
- Installing Firmware (Main Firmware)313
  - Checking Firmware Version313
  - Installing Firmware314
- Adjusting Left-End and Upper-End Print Position (TT Only)315
Chapter 5 Service Functions316
Maintenance Mode316
- How to Enter Maintenance Mode316
  - Method of Entering Maintenance Mode for Service Personnel316
  - Method of Entering End-User Accessible Maintenance Mode317
- List of Maintenance Mode Functions318
- Details of Maintenance Mode Functions320
Other Service Functions376
- Print Communication Error List376
- Reset the Drum Unit Counter376
Chapter 6 Wiring Diagram377
- Wiring Diagram377
Chapter 7 Periodical Maintenance380
Safety Precautions380
Periodical Replacement Parts381
- Preparation381
- Fuser Unit382
- Laser Unit386
- PF Kit MP396
- PF Kit 1397
- PF Kit 2/3/4/5399
Appendix 1 Serial Numbering System401
Appendix 2 Deleting User Setting Information402
Appendix 3 Installing the Maintenance Printer Driver403

Brand	Brother
Model	MFC-8540DN
Category	All in One Printer
Language	English

Brother MFC-8540DN Service Manual

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