Brother MFC8420 Service Manual page 246

I-21 Horizontal lines
Possible cause Step
Paper feed roller 1
Paper tray 2
contacts
I-22 Light rain
Possible cause Step
Drum unit failure 1
Drum 2
connection
failure
High-voltage 3
power supply
PCB failure
Check
Are the feed roller shaft and
the ground contact connected
correctly?
Are the ground contacts on the
back side of the paper tray
connecting correctly?
Check
Is the problem solved after
replacing the drum unit?
Is the contact between the
drum unit and machine
connected correctly?
Is the problem solved after
replacing the high-voltage
power supply PCB?
6-51
MFC-8420/8820D/8820DN, DCP-8020/8025D/8025DN
Result Remedy
No Check the connection
between the shaft and
the ground contact.
Also check the ground
contact on the back of
the feed roller.
No Clean the contacts.
Remedy
Result
Yes Replace the drum
unit.
No Clean contact
electrode both on the
drum unit and in the
machine.
Yes Replace the high-
voltage power supply
PCB.
SERVICE MANUAL
Ground
contacts
(7)
Ground
contact
(8)