Brother HL-4000CN Service Manual page 285

11.3 Toubleshooting Table by Trouble Phenomena
<Fogging>
Condition:
Fogging over print. Toner attaches to margin of print.
Initial check:
Parts of different specifications, improper installation, damage, deformation, dirt, foreign
substance attached, etc.
Major parts to be checked:
Print head cartridge ASSY, Fuser ASSY, Transfer roll cartridge ASSY, Scanner ASSY,
MCU and HVPS PWB, SUB HVPS
Item Check
Faulty print head cartridge ASSY
1 Is the image quality improved if print head cartridge
ASSY is replaced?
Faulty scanner ASSY
2 Is the image quality improved if scanner ASSY is
replaced?
Faulty fuser ASSY
3 Check the heat roll and NIP belt for evidence of
damage, dirt, or foreign substances.
Faulty transfer roll cartridge ASSY
4 Is the image quality improved if transfer roll
cartridge ASSY is replaced?
Fig.5-17
V-75
Remedy
Replace the print head
cartridge ASSY
Replace the scanner
ASSY
Replace the fuser ASSY
Replace the transfer roll
cartridge ASSY