Brother MFC8420 Service Manual page 228

Speaker is silent during on-hook dialing.
F-5
Possible cause Step
Connection 1
between main
PCB and
speaker
Speaker 2
Connection 3
between main
PCB and NCU
PCB
Harness 4
between main
PCB and NCU
PCB
Connection 5
between main
PCB, relay PCB,
and control
panel PCB
Harness 6
between main
PCB, relay PCB,
and control
panel PCB
NCU PCB 7
Relay PCB 8
Main PCB 9
Dialing function does not switch between "tone" and "pulse".
F-6
Possible cause Step
Connection 1
between main
PCB and NCU
PCB
Harness 2
between main
PCB and NCU
PCB
NCU PCB 3
Main PCB 4
Check
Main PCB and speaker are
properly connected.
Replacement of speaker
solves the problem.
Main PCB and NCU PCB are
properly connected.
Harness wire is damaged.
Main PCB, relay PCB, and
control panel PCB are
properly connected.
Harness wire is damaged.
Replacement of NCU PCB
solves the problem.
Replacement of relay PCB
solves the problem.
Replacement of main PCB
solves the problem.
Check
Main PCB and NCU PCB are
properly connected.
Harness wire is damaged.
Replacement of NCU PCB
solves the problem.
Replacement of main PCB
solves the problem.
6-33
MFC-8420/8820D/8820DN, DCP-8020/8025D/8025DN
Result Remedy
No Fix the connection properly.
Yes Replace the speaker with a
normal part.
No Fix the connection properly.
Yes Replace the harness with a
normal part.
No Fix the connection properly.
Yes Replace the harness with a
normal part.
Yes Replace the NCU PCB with
a normal part.
Yes Replace the relay PCB with a
normal part.
Yes Replace the main PCB with
a normal part.
Result Remedy
No Fix the connection properly.
Yes Replace the harness with a
normal part.
Yes Replace the NCU PCB with
a normal part.
Yes Replace the main PCB with
a normal part.
SERVICE MANUAL