Kenwood TK-390 Service Manual page 18

3-4. Wide/Narrow changeover circuit
Narrow and Wide settings can be made for each channel
by switching the MCF; XF300 (Wide), XF301 (Narrow) with
the ceramic filters CF300, CF301 (Wide), CF302, CF303
(Narrow).
The WIDE (high level) and NARROW (low level) data is
output from IC400 (I/O port expansion) pin 4.
When a WIDE (high level) data is received, Q300, Q303
turn off and Q301, Q304 turn on. When a NARROW (low
level) data is received, Q300, Q303 turn on and Q301, Q304
turn off. D300, D301 switch to MCF or D302, D303 are
switched to ceramic filters when a high/low level data is re-
ceived.
Q305 turns on/off with the Wide/Narrow data and the
IC300 detector output level is changed to maintain a con-
stant output level during wide or narrow signals.
IC200
5R
Q300
D300
Q301
Fig. 3 Wide/Narrow changeover circuit
5R
R322
Q302
5R
Q303
D302
Q304
Fig. 4 Wide/Narrow changeover circuit
CIRCUIT DESCRIPTION
W/N
XF300
44.85MHz (W)
R305 R307
XF301
D301
44.85MHz (N)
Q302
R306 R308
Q307
Q305
W/N "H" : Wide
"L" : Narrow
IC300
FM IF SYSTEM
W/N
CF300 CF301
D303
CF302 CF303
3-5. 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
MIX, DET, IF
CF300
X300
CF301
2nd local
OSC
CF302
CF303
2 1
IC607
HPF LPF HPF BEF
DE-
EMP
5
Fig. 5 Audio amplifier circuit
3-6. Squelch circuit
The output signal from the squelch circuit, which con-
sists of IC605 (2/2) and Q600, is applied to the microproces-
sor. The microprocessor passes information to the shift reg-
ister (IC403) and it controls the mute control lines (AMP SW,
INT AFC, and EXT AFC) according to the input signal (noise
pulse) and the microprocessor task condition.
IC601 IC605
(2/2) (2/2) Q600
From AF
HPF CLIP
DET AMP
Fig. 6 Squelch circuit
TK-390
SB
Q6
Q5
AMP SW
IC1
5
Q8 Q7
13
AF
4 16
SW SW INT.SP
2
INT AFC
Q15
9
6 12
SW
EXT.SP
8
EXT AFC
IC604 (2/2)
IC603 AF AMP
EXP MUTE VOL
41
IC403
IC406
42 AMP SW
BUSY
OUTPUT
INT AFC
EXPANDER
CPU
EXT AFC
AF
17