Brother MFC-9420CN Service Manual page 288

I-8 Vertical White Band
Phenomenon
White band appears in the vertical direction of printed image as shown in
Main Causes
(1) Failure of the toner cartridge PU (blade).
(2) Stain of the OPC charger roller PU.
(3) Stain of the OPC belt.
(4) Stain of the transfer belt.
Transfer belt
Transfer unit PU
Countermeasures
(1) Replace the toner cartridge PU with a new toner cartridge PU.
(2) Replace the belt cartridge PU with a new belt cartridge PU.
(3) Replace the transfer unit PU with a new transfer unit PU.
OPC belt
Fig. 9-9
9 - 3 2
print sample [8] of Fig.9-1.
Belt cartridge PU
Toner cartridge PU
(K, Y, M, C)
OPC charger roller PU
Confidential