Icom IC-M400BB Service Manual page 25

July 2013
RX AF CIRCUIT (MAIN UNIT)
The demodulated AF signal from the AF SW (IC504B)
is passed through the BPF (IC506B, IC506C) and AF SW
(IC901, pins 7, 1), and then applied to the noise canceller IC
(IC902, pin 36).
The processed AF signal is output from pin 25, and then
passed through the LPF (IC905, pins 1, 4) and AF SW
(IC904, pins 1, 7).
• When the AF signal is output to the optional COM-
MANDMICIV™
The RX AF signal from the AF SW (IC904, pins 1, 7) is passed
through the AF MUTE SW (IC503A, pins 2, 1) and amplifi ed
by the buffer (IC506A), and then output to the COMMANDMI-
CIV™, through the AF mute SW (IC502D, 11, 10).
• RX AF CIRCUIT
From the IC901 IC902
demodulator circuits
AF
From the
CANCELLER
SW
TX AF circuits
IC905 IC503B
IC904
FILO
AF
NOISE AF
LPF
MUTE
SW
IC503A
To the
modulation
AF
circuits
MUTE
MAIN UNIT
• When the AF signal is output to the external speaker
The RX AF signal from the AF SW (IC904, pins 1, 7) is passed
through the AF MUTE SW (IC503A, pins 2, 1) and amplifi ed
by the buffer (IC506A), and then output to the external speak-
er, through the AF mute SW (IC502D, 11, 10).
IC515B IC514
IC702A
AFVOLO
VOL1 AFVOLI PRE
AF
AMP
AMP
IC506A
SAFO
BUFF
TX AF CIRCUITS
4-2
CHASSIS
IC704
IC701A
AF
AF
AMP
MUTE
IC502D
AF
MUTE
COMMANDMIC
External
speaker