Kenwood TM-631A Service Manual page 16

TM-631A
CIRCUIT DESCRIPTION
©
Shift Register Circuit
By
shifting serial data from
the
microprocessors,
the two shift
registers (IC3 and IC4) perform the following control functions:
@
Main and sub standby control
¢ Muting control
Low power
control
Electronic volume control, UP/DOWN switching
¢
Dimmer control
®
Main/sub select
®
Squelch
off control
®
CTCSS
MAIN, SUB select
©
Dimmer Control Circuit
Fig.
21
shows
the
AVR
circuit
in
the LB. The LB (Lamp
+B)
voltage
is
lowered
by
switching
the reference voltage zener
diodes.
Normally the base voltage of Q2
is
held to
approximately 11
V
by the
11
V
zener diode D1:02CZ11Y, and the pilot lamp vol-
tage LB
is
approximately 10.5 V. When the
DIM
switch
is
set
to the ON
position,
5
V
dc
is
obtained from
pin
4 of shift register
IC3, causing
03 DCT 114EKto
go from High to
Low, thereby
connecting zener
diode
D2:02CZ8-2Y
in parallel to
D1.
Therefore,
the base voltage of Q2
is
held to the zener voltage
(8.2 V) of
D2, resulting
in a
drop to
approximately
8.5 V.
The
pilot lamp
voltage
LB then drops
to
approximately 7.8
V
and
the pilot lamp dims.
10.5
V
(7.8
V
with
R2
RI
OK
470
dimmer ON)
WW
02
(8.5
V
with
3
Ol
dimmer ON) 2
11.2V
02 02CZ8.2Y
(8.5 V
with Q3
dimmer ON)
>
N
SHIFT
REGISTER
IC3(4pm)
D2 parallels
D1
Ov
when dimmer
is ON
{5.0
V
with
dimmer ON)
Fig.
21 LB
(Lamp
+B) AVR
Circuit
©
Squelch-Off Circuit (When RC-10
is Connected)
Fig.
22
shows the squelch-off circuit. This circuit opens the
squelch gate
for the main band from the remote controller
when
the remote control unit
is
used.
When
the
RC-10
is
connected, it
communicates with the
microprocessor
in
the set via pins
2, 3,
and 4 of the micro-
phone
connector. When
the
RC-10
is connected,
the
exchange
of data with the microprocessor causes
pin
11
of
shift register
IC3 to provide
a
High switch control signal, so transistor Q9
goes Low
and the
SQL
pin is
dropped to ground level.
The result
is
that the squelch
VR
for the main band
is
left
open.
Part of the main noise
amplifier output
is
fed from the RD (Re-
mote Data)
pin
to
pin
6 of the microphone connector, and from
there to the
RC-10.
(MAIN)
NOISE AMP
AF
AMP
ICS
IC
6
KCAO!
KCA02
98
2
98
2
From
IC4 pin 5
r ?
\
a9
so
L
RI4
RDM
ve
Microphone
connector
cio
R7
o
From shift register
IC3
(pin
11)
RC-10 connector
Al
Fig.
22 Squelch Off Circuit
LB
*
Beep
Tone
The microprocessor generates
a
beep tone of approximately
1.2 kHz
at
pin
P20. This signal
is
reshaped
into
a
rectangular
wave
by an C,
R
wave-shaping circuit.
CSB
11.2V
a
144
TX-RX
unit
To IC3 14
pin
Ic!O}
P20
Ko
2
c2
from
MAIN
AF-LPF
output
Fig. 23
15
pin
11