Malfunctions - Brother MFC8420 Service Manual

5.

MALFUNCTIONS

When taking countermeasures for malfunctions as described in this section, check connectors
for contact failure before measuring the voltage at the specified connector pins.
M-1 No AC power supplied
Possible cause Step
Supply voltage 1
Power plug 2
Fuse (F1, F2) 3
Wiring 4
M-2 No DC power supplied
Possible cause Step
AC power 1
supply
Wiring, DC load 2
Low-voltage 3
power supply
PCB
*1
PCB +lead pin
Engine CN8-3
CN10-6
Check
Is the correct voltage present
at the outlet?
Is the power cord securely
plugged into the outlet?
Is the fuse blown?
Unplug the power supply plug.
Is there a broken wire between
the AC input connector of the
low-voltage power supply and
the power plug?
Check
Is AC power supplied between
connectors CN1-L and CN1-N
when the power plug is
plugged into the outlet?
Turn on the power switch.
Measure the voltages between
the terminals. Do the
measured voltage satisfy the
prescribed valued in the table
below?
Refer to the chart *1 below.
- lead pin Voltage
CN8-2 Approx. 24V
CN10-5 Approx. 3.3V
6-23
MFC-8420/8820D/8820DN, DCP-8020/8025D/8025DN
Result Remedy
No Inform the user that the
correct voltage is not supplied
at the outlet.
No Plug the power cord securely
into the outlet.
Yes If the fuse blows again
immediately after replacing
the low-voltage power supply
PCB, check that there is not a
short circuit somewhere in the
AC power supply line.
Yes Replace the AC power cord.
Result Remedy
No Follow the same check
procedure of M-1 "No AC
power supplied".
Yes Turn off the power switch,
reconnect the connector and
turn the power switch on
again. If the protector circuit
is activated, check the
connector, the wiring from the
connector, and the DC load.
No Replace the low-voltage
power supply PCB.
SERVICE MANUAL