Brother MFC-9420CN Service Manual page 298

I-18 Mottle
Phenomenon
Variation of the optical density is found in the image as shown in
Main Causes
(1) The back cover ASSY is not fixed in place.
(2) Installation of the transfer roller is not accurate.
(3) THV output of DC high voltage unit is not normal.
(4) Failure of the toner cartridge PU.
(5) Deformation of the print paper.
Fusing Unit FU
Back cover ASSY PU
Transfer roller ASSY PU
Registration roller ASSY PU
Transfer unit PU
Paper feed roller PU
Countermeasures
(1) Confirm if the back cover ASSY PU is firmly locked or not.
(2) Replace the papers with new papers.
(3) Replace the toner cartridge PU with a new toner cartridge PU.
(4) Confirm if the transfer roller ASSY PU is properly installed or not.
(5) Replace the HV power supply unit PU with a new HV power supply unit PU.
Fig. 9-19
9 - 4 2
print sample [18] of Fig.9-1.
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