Brother Facsimile Equipment MFC7420 - Manual (Page 219)

Confidential 9-31
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 Check Result Remedy Ground
contacts
1 Is the corona wire dirty? Yes Clean the corona wire
with the wire cleaner.
(2)
2 Is the corona wire broken? Yes Replace the drum unit.
Corona failure
3 Are the charge electrodes
between the printer body
and the drum unit dirty? Yes Clean both electrodes.
(3)
Harness
connection 4 Is the laser unit connected
to the main PCB correctly? No Connect the harness
between the laser unit
and the main PCB
correctly.
High-voltage
power supply
PCB failure 5 Is the problem solved after
replacing the high-voltage
power supply PCB? Yes Replace the high-
voltage power supply
PCB.
Main PCB
failure 6 Is the problem solved after
replacing the main PCB? Yes Replace the main PCB.
Laser unit
failure 7 Is the problem solved after
replacing the laser unit? Yes Replace the laser unit.