Brother HL-1850 Service Manual page 223

I-4 All black
User Check
(1) Clean the corona wire of the drum unit.
(2) The drum unit may be damaged. Install a new drum unit.
Possible cause Step
Corona failure 1
2
3
Harness 4
connection
High-voltage 5
power supply
PCB failure
Main PCB failure 6
Check
Is the corona wire dirty?
Is the corona wire broken?
Are the charge electrodes
between the printer body and
the drum unit dirty?
Is the laser unit connected to
the main PCB correctly?
Is the problem solved after
replacing the high-voltage
power supply PCB?
Is the problem solved after
replacing the main PCB?
6-39
HL-1850/1870N SERVICE MANUAL
Result Remedy
Yes Clean the corona wire
with the wire cleaner.
Yes Replace the drum
unit.
Yes Clean both electrodes.
No Connect the harness
between the laser unit
and the main PCB
correctly.
Yes Replace the high-
voltage power supply
PCB.
Yes Replace the main
PCB.
Ground
contacts
(2)
(3)