Brother MFC 9840CDW - Manual (Page 174)

158
Cleaning the corona wires
C
If you have print quality problems, clean the
corona wires as follows:
a
Turn off the machine’s power switch.
Unplug the telephone line cord first,
disconnect all cables, and then unplug
the power cord from the AC power
outlet.
b
Press the front cover release button and
then open the front cover.
c
Hold the green handle of the drum unit.
Lift the drum unit up and then pull it out
until it stops.
d
Hold the handle of the toner cartridge
and pull it out of the drum unit. Repeat
this for all the toner cartridges.