Brother MFC8420 Service Manual page 236

I-7 Black and blurred horizontal stripes
User Check
(1) The drum unit may be damaged. Install a new drum unit.
(2) Check the paper used meets the recommended paper specifications.
(3) Clean the machine interior and the corona wire in the drum unit.
Possible cause Step
Scratch on the 1
drum
Toner stuck on 2
the developer
roller
Scratch on the 3
heat roller
Corona contact 4
failure
High-voltage 5
power supply
PCB failure
I-8 Black vertical streaks (in a gray background)
Possible cause Step
Translucent 1
stain on the
scanner window
Corona failure 2
Check
Are the horizontal stripes at
94mm (photosensitive drum)
intervals?
Are the horizontal stripes at
39mm (developer roller)
intervals?
Are the horizontal stripes at
79mm (heat roller) intervals?
Are the charge electrodes
between the machine and the
drum unit dirty?
Is the problem solved after
replacing the high-voltage
power supply PCB?
Check
Is there any dirt on the scanner
window?
Is the corona wire dirty?
6-41
MFC-8420/8820D/8820DN, DCP-8020/8025D/8025DN
Result Remedy
Yes The photosensitive
drum was scratched.
Replace the drum
unit.
Yes After printing several
pages, the problem
will disappear.
If not, replace the
toner cartridge.
Yes Replace the heat
roller.
Yes Clean both electrodes.
Yes Replace the high-
voltage power supply
PCB.
Result Remedy
Yes 1) Clean the scanner
window.
2) If it is not effective,
replace the laser
unit.
Yes Clean the corona wire
with the wire cleaner.
SERVICE MANUAL
Ground
contacts
(3)
Ground
contacts
(2)