Brother HL-1070 - B/W Laser Printer Service Manual page 72

I-4 All black
Possible cause Step
Corona failure 1
2
Harness 3
connection
H.V. power 4
supply PCB
Ditto 5
Main PCB 6
Driver PCB 7
Check
Is the corona wire of the drum
unit broken?
Are the electric terminal
springs in the printer body and
the electrode on the bottom
face of the drum unit dirty?
Is the scanner unit connected
with the driver PCB correctly?
Is the problem solved after
H.V. power supply PCB
replaced?
Perform the same check as in
step 3.
Is the problem solved after
main PCB replaced?
Is the problem solved after
driver PCB replaced?
IV-8
Result Remedy
Yes Replace the drum
unit.
Yes Clean the terminals
in the printer and on
the drum.
Yes Check the harness
connection between
the scanner unit and
the driver PCB.
Yes Replace the H.V.
power supply PCB.
No Replace the panel
sensor PCB.
Yes Replace the main
PCB.
Yes Replace the driver
PCB.
HV.GND
contacts
(Fig.4-5)