Brother MFC-8220 Service Manual page 208

CHAPTER 6 TROUBLESHOOTING
No dial tone
F-7
Possible cause
Connection
between main
PCB and NCU
PCB
Harness
between main
PCB and NCU
PCB
NCU PCB
Main PCB
Step Check
Main PCB and NCU PCB are
1
properly connected.
Harness wire is damaged.
2
Replacement of NCU PCB
3
solves the problem.
Replacement of main PCB
4
solves the problem.
Result
No
Yes
Yes
Yes
6-30
Remedy
Fix the connection properly.
Replace the harness with a
normal part.
Replace the NCU PCB with
a normal part.
Replace the main PCB with
a normal part.