Brother HL-820 Service Manual page 73

I-2 Dark
Possible cause Step
Corona failure 1
(soiled wire)
Corona failure 2
(contact failure)
Drum unit failure 3
High-voltage 4
power supply
PCB
Main PCB 5
Panel sensor 6
PCB
Check
Is the corona wire dirty?
Are the corona electrodes
between the printer body and
drum unit dirty?
Is the problem solved when the
drum unit is replaced?
Are there any disconnected
connectors?
Are there any disconnected
connectors?
Are there any disconnected
connectors?
IV-6
Result Remedy
Yes Clean the corona wire
by using the wire
cleaner.
No Clean both electrodes.
Yes Replace the drum
unit with a new one.
No Replace the high-
voltage power supply
PCB.
No Replace the main
PCB.
No Replace the panel
sensor PCB.
HV.GND
contacts
(Fig.4-5)