Kenwood TK-190 Service Manual page 13

3-4. Audio amplifier circuit
• TX-RX unit
The demodulated signal from IC300 goes through IC301,
and is amplified by IC601 (2/2), high-pass filtered, low-pass
filtered, high-pass filtered, band-eliminate filtered, and de-
emphasized by IC607.
The signal then goes through an electronic volume con-
trol (IC603), an AF amplifier IC604 (2/2), and an AF switch
(Q8 is on and Q7 is on of the control unit), and is routed to
audio power amplifier (IC1 of the control unit), where it is
amplified and output to the internal speaker.
• Control unit
The audio mute signal (AMP SW) from the microproces-
sor becomes Low in the standby and Q5, Q6 which are
power supply circuit for IC1 turn off. When the audio is out-
put, AMP SW becomes High to turn Q5, Q6 on, and voltage
is supplied to power terminal VP of IC1.
Speaker switching is done from IC403 (TX-RX unit) by INT
AFC or EXT AFC. First, the logic level at the speakers
switching terminal (SSW) on the universal connector is input
to the microprocessor (IC406 TX-RX unit). The microproces-
sor then outputs data to IC403 based on this input.
When there is no SP-MIC installed, this logic level is high.
When the INT AFC is high, the EXT AFC goes low, so the AF
signal is only input to the amplifier for the internal speaker
(INT SP) of IC1. However, when a SP-MIC has been in-
stalled, this logic level is low, so the INT AFC goes low and
the EXT AFC goes high. So that the AF signal is input only to
amplifier for the external speaker (EXT SP) of IC1.
IC601(2/2)
AF AMP
IC301
IC300
SW
FM IF SYSTEM
129.005MHz
CF300
455kHz
1
2
IC607
HPF LPF HPF BEF
5
Fig. 3 Audio amplifier circuit
CIRCUIT DESCRIPTION
Q5,6
SB SW
AMP SW IC1
13
Q8 Q7
5
AF
4
16
INT.SP
SW SW
2
INT AFC
9
6
12
SW EXT.SP
8
EXT AFC
IC604(2/2)
AF AMP
IC603
DE-
EXP MUTE VOL
EMP
41
3-5. Squelch circuit
It amplifies the demodulated noise signal from FM IC
(IC300) after filtering through BPF circuit. Then, the ampli-
fied signal is coverted to DC signal by the detection circuit.
The coverted signal is feeded through the microprocessor
(IC 406) and the voltage level is detected by ADC (A/D con-
verter) to control the squelch circuit.
AF
OUT
9 8
IC300
7
DET NOISE
OUT AMP
Fig. 4 Squelch circuit
AF
TK-190
IC406 IC403
Q304 D301
42
NOISE BUSY OUTPUT
DET
AMP CPU EXPANDER
AMP SW
INT AFC
EXT AFC
13