Brother MFC-9420CN Service Manual page 258

I-7 White Line (2)
Phenomenon
Vertical white line appears from the leading edge to the trailing edge of printed image as shown in
print sample [7] of Fig.9-1.
Main Causes
(1) Dustproof glass of laser ASSY PU is smeared with toner or foreign particles.
(2) Hairy foreign particles adhere to the laser beam opening of laser ASSY PU.
(3) There are foreign particles mixed in the toner cartridge PU.
OPC belt
Countermeasures
(1) Clean the dustproof glass.
1) Remove the belt cartridge PU and toner cartridge PU.
2) Open the developer cover.
3) Clean the dustproof glass.
(2) Clean the laser beam opening of laser ASSY PU.
(3) If white line II failure is attributed to toner cartridge PU, replace it with a new cartridge PU.
Belt cartridge PU
Toner cartridge PU
(K, Y, M, C)
Cover C
Laser ASSY PU
Fig. 9-8
9 - 3 1
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Dustproof cover
Dustproof glass
cleaning area
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