Brother Facsimile Equipment MFC7420 - Manual (Page 217)

Confidential 9-29
I-2 Dark
User Check
(1) Check the paper used meets the recommended paper specifications.
(2) Check the printer’s environment. High temperature and high humidity
conditions can increase the amount of background shading.
(3) Clean the corona wire with the wire cleaner.
(4) Try installing a new toner cartridge or drum unit.
Possible cause Step Check Result Remedy Ground
contacts
Corona failure
(contact
failure) 1 Are the charge electrodes
between the printer body
and the drum unit dirty? Yes Clean both electrodes.
(3)
Drum unit
failure 2 Is the problem solved after
replacing the drum unit? Yes Replace the drum unit
with a new one.
Toner
cartridge
failure 3 Is the problem solved after
replacing the toner
cartridge? Yes Replace the toner
cartridge with a new
one.
High-voltage
power supply
PCB failure 4 Is the connections of the
connector between the
high-voltage power supply
PCB and the main PCB
secured correctly? Yes Replace the high-
voltage power supply
PCB.
Main PCB
failure 5 Are there any disconnected
connectors? No Replace the main PCB.