Brother MFC-9420CN Service Manual page 295

I-15 White Spot / Black Spot
Phenomenon
White spots and black spots appear on the print as shown in
Main Causes
(1) Foreign particles adhere to the OPC belt or the transfer belt.
(2) The OPC belt or the transfer belt is damaged.
(3) Foreign particles mixed in the toner.
(4) Foreign particles adhering to the transfer roller PU, or local deformation of transfer roller PU.
Back cover ASSY PU
Transfer belt
Transfer roller PU
Countermeasures
(1) Remove the belt cartridge PU.
1) Lightly wipe off the foreign particles adhering to OPC belt, using cotton cloth.
2) Replace the damaged belt cartridge with a new cartridge.
(2) Open the back cover ASSY PU, and check the transfer belt surface.
1) With the cotton cloth, lightly wipe off the foreign particles adhering to the transfer belt.
2) Replace the damaged back cover ASSY PU with a new back cover ASSY PU.
(3) Remove the toner cartridge PU.
1) Replace the toner cartridge PU with a new cartridge PU.
(4) Replace the transfer roller ASSY PU with a new transfer roller ASSY PU.
OPC belt
Fig. 9-16
9 - 3 9
print sample [15] of Fig.9-1.
Belt cartridge PU
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