Brother HL-1070 - B/W Laser Printer Service Manual page 70

I-2 Dark
Possible cause Step
Density dial 1
Corona failure 2
(soiled wire)
Corona failure 3
(contact failure)
Drum unit failure 4
H.V. power 5
supply PCB
Main PCB 6
Driver PCB 7
Check
Is the density dial at the center
click position?
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
No Set it to the center
click position or
reasonable position.
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 H.V.
power supply.
No Replace the main
PCB.
No Replace the driver
PCB.
HV.GND
contacts
(Fig.4-5)