Icom IC-M506 Service Manual page 11

RX AF CIRCUITS (MAIN UNIT)
The demodulated AF signal from the AF SW (IC882) is passed
through the AF MUTE SW (IC505, pins 1, 2), de-emphasis
circuit (R551 and C236), BPF (IC506, pins 9, 8 and pins 6, 7)
and AF MUTE SW (IC906, pins 9, 8), and then applied to the
noise canceller IC (IC901, pin 31).
The processed AF signal is output from pin 37, and passed
through the AF SW (IC906, pins 1, 2).
• When the AF signal is output to the front panel speaker,
external speaker, HM-205B or HM-205RB
The RX AF signal from the AF SW (IC906, pin 2) is passed
through the AF MUTE SW (IC504, pins 8, 9) and applied to
the D/A converter (IC702, pin 8) to be adjusted in level. The
level-adjusted signal is output from pin 7, and amplifi ed by
the AF AMP (IC707). The amplifi ed signal is AF power AMP
(IC701, pin 1), through the AF MUTE SW (IC703, pins 3, 1).
The amplifi ed signal is output to the internal speaker (CHAS-
SIS: SP1), external speaker, HM-205 or HM-205RB.
• RX AF CIRCUITS
HM-205RB
HM-205B
SP1 SP1
INT SP
SP1 R
IC701A
1
AF
AMP
EXT SP(BTL AMP)
IC906C
From the
demodulator circuits
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FRONT UNIT
MAIN UNIT
IC706 IC503B:
IC704 IC702A
AF AF
AF EVOL
AMP 1A MUTE
MUTE
IC906B
IC901
AF
AF NOISE MUTE
IC906A
CANCELER
MUTE
Rec_Play
(2CH) AF
X901 MUTE
IC504C:
IC703
IC702B
IC707 IC701B
AF
AF
EVOL AF
MUTE
1B AMP MUTE
• When the AF signal is output to the optional HM-195
The RX AF signal from the AF SW (IC906, pin 2) is passed
through the AF MUTE SW (IC503, pins 2, 1) and amplifi ed by
the buffer (IC506, pins 4, 1), and then output to the HM-195,
through the AF mute SW (IC502, pins 9, 8).
IC503A: IC506A:
IC502C:
AF AFMIC
AF
BUFF
MUTE
MUTE
RL1
Q702
D702
Relay
AF
AMP
4-2
HM-195
OPTIONAL
COMMANDMIC
PA SP
(BTL AMP)