Brother MFC8420 Service Manual page 219

CHAPTER 6 TROUBLESHOOTING
If you analyze malfunctions with the power plug inserted into the power outlet, special
caution should be exercised even if the power switch is OFF because it is a single pole
switch.
M-3
Possible cause
Failure of
connector
Main motor
Engine PCB
Main PCB
M-4
Possible cause
Failure of
connector
Engine PCB
circuit
Paper pick-up
clutch solenoid
Separation pad /
pick-up roller
failure
Main PCB
Main motor failure
Step Check
1 Is the connection of connector
CN9 on the engine PCB
correct?
2 Is the problem solved by
replacing the main motor?
3 Is the problem solved by
replacing the engine PCB?
4 Is the problem solved by
replacing the main PCB?
No paper supplied
Step Check
1 Is the contact of the solenoid
connector on the engine PCB
good?
2 Set paper in the manual paper
slot and make a test print by
pressing the control panel
button.
Does the voltage between pins
2 (SOLENOID) and 1 (24V) of
the CN16 connector on the
engine PCB change from
approx. 24V DC to 0V within
the specified time?
3 Is the surface of the separation
pad or the pick-up roller dirty or
worn out?
4 Is the problem solved by
replacing the main PCB?
WARNING
Result
No Reconnect the connector.
Yes Replace the main motor.
Yes Replace the engine PCB.
Yes Replace the main PCB.
Result
No Reconnect the connector.
Yes Replace the engine PCB.
No Replace the paper pick-up
solenoid.
Yes 1) Clean the surface of the
2) Replace the separation
Yes Replace the main PCB.
6-24
Remedy
Remedy
separation pad or pick-up
roller.
pad or pick-up roller.