Brother HL-4000CN Service Manual page 287

<Streak in the shaft direction>
Fig.5-20
Condition:
Black or white streaks in the shaft direction.
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?
Check periodicity
5 Periodicity found
Faulty ESS PWB
6 Is the image quality improved if ESS PWB is
replaced?
V-77
Fig.5-21
Remedy
Replace the print head
cartridge ASSY
Replace the scanner
ASSY
Replace the fuser ASSY
Replace the transfer roll
cartridge ASSY
Replace the parts
concerned.
See the table below
Replace the ESS PWB