Brother MFC6800 Service Manual page 141

Modem error details (Code 3)
Code 3
21 Timeout waiting for INFO0.
22 Checksum error in INFO0.
23 Timeout waiting for tone A or B.
24 Timeout waiting for first phase reverse.
25 Timeout waiting for probing cut-off tone.
26 Timeout waiting for second phase reverse.
27 Timeout waiting for end of probing.
28 Timeout waiting for third phase reverse.
29 Timeout waiting for INFO1.
2A Checksum error in INFO1.
2B Tone detected preceding INFO0.
2C Unexpected INFO0 detected.
31 Timeout waiting for turning off the receive control channel.
91 Error occurred in the first CC train.
92 Timeout waiting for PPh.
93 Tone A/B detected in the CC retrain.
94 Timeout waiting for ALT.
95 ACh found.
96 FED turned off during reception of CC data.
97 Timeout waiting for turning off the CC.
A1 Retraining forced for problems not fixed in phase 2.
B0 Problem with S-sequence of HDX-resync.
B1 FED turned off in the S-sequence of HDX-resync.
B2 S-sequence finished before prediction in HDX-resync.
B3 Timeout waiting for S-Sbar in HDX-resync.
B4 Timeout waiting for S-Sbar in HDX-resync.
B5 Timeout waiting for S in HDX-resync.
B6 Timeout waiting for synchronization with PP.
C0 Problem with S-sequence in phase 3.
C1 FED turned off in the S-sequence in phase 3.
Causes
6 -1 4