Kenwood TK-2180 Service Manual page 12

TK-2180
7-2. Decode
■ Low-speed data (QT, DQT)
The demodulated signal from the IF IC (IC200) is amplified
by IC600 (1/2) and passes through a low-pass filter (IC607) to
remove audio components. The signal is input to pin 128 of
the CPU.
The CPU digitizes this signal, performs processing such as
DC restoration, and decodes the signal.
■ High-speed data (DTMF)
The DTMF input signal from the IF IC (IC200) is amplified
by IC600 (1/2) and goes to IC607, the DTMF decoder. The
decoded information is then processed by the CPU. During
transmission and standby, the DTMF IC is set to the power
down mode.
IC607
IC600
AMP LPF
LPF
DTMF
DECODE
XIN
X600
Fig. 13 Decode
12
CIRCUIT DESCRIPTION
IC201 IC305
COM-
HPF AMP
PARATOR
10
HSDIN
128
LSDIN
DTRLOAD
IC502
STD
CPU
DTRCLK
XOUT
DTRDO
F400
+B
RF power amp
2.5A
D405
VIN
VOUT
IC400
Q409
SAVE
Fig. 14 Power supply circuit
■ High-speed data (5-tone)
The demodulated signal from the IF IC (IC200) is amplified
by IC600 (1/2) and passes through an audio processor (IC607)
and amplifier IC604 (1/2) and comparator IC604 (2/2) to re-
move a low-speed data. The CPU digitizes this signal and
decodes the signal.
■ MSK
The MSK input signal from the IF IC is amplified by IC600
(1/ 2) and goes to pin 5 of IC607. The signal is demodulated
by MSK demodulator in IC607. The demodulated data goes
to the CPU for processing.
8. Power Supply Circuit
Battery +B is supplied via a 2.5A fuse from the battery
terminal connected to the TX-RX unit. Power supply (+B) is
applied to the four AVRs. IC402 supplies 5V (5M) to the con-
trol circuit. IC401 and IC403 supplies 5V to common circuits.
IC406 supplies to the TX circuit, the RX circuit and common
circuits. During transmission, 5TC becomes Low and Q406
is turned on to supply 5V (5T) to the TX circuit. During recep-
tion, 5RC becomes Low and Q405 is turned on to supply 5V
(5R) to the RX circuit.
The power supply voltage monitor IC (IC400) monitors
power supply voltage (+B). If the voltage falls (less than
5.6V), the VOUT port goes "LOW" level, the CPU INT port
also goes "HIGH" level, and the CPU stops.
IC402
Q408
5M
VOUT
VIN
VDD
CE
OUT
IC405
Q407
D403
Q401
IC403
VIN
VOUT
5C
CE
IC401
VIN
5CNS
VOUT
CONT
5R
Q405
IC406
5RC
VIN
VOUT 5T
CONT
Q406
5TC
IC502
CPU
RESET
INT
PSW
Q502