Brother MFC-9420CN Service Manual page 290

F-5
Speaker is silent during on-hook dialing.
Possible cause
Step
Connection 1
between main
PCB and speaker
Speaker 2
Connection 3
between main
PCB and NCU
PCB
Harness between 4
main PCB and
NCU PCB
Connection 5
between main
PCB and control
panel PCB
Harness between 6
main PCB and
control panel PCB
NCU PCB 7
Main PCB 8
F-6
Dialing function does not switch between "tone" and "pulse".
Possible cause
Step
Connection 1
between main
PCB and NCU
PCB
Harness between 2
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 is damaged.
Main PCB and control
panel PCB are properly
connected.
Harness is damaged.
Replacement of NCU
PCB solves the problem.
Replacement of main
PCB solves the problem.
Check
Main PCB and NCU
PCB are properly
connected.
Harness is damaged.
Replacement of NCU
PCB solves the
problem.
Replacement of main
PCB solves the
problem.
9 - 6 3
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Remedy
Result
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 main PCB with a
normal part.
Remedy
Result
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
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