Kenwood TK-7302 Service Manual page 14

TK-7302/7302 V /7302H/7302H
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■ High-speed data (2-tone)
The demodulated signal from the FM IC (IC500) is am-
plifi ed by the baseband IC and passes through a high-pass
fi lter to remove frequencies of 3kHz or more. The MCU digi-
tizes this signal and decodes the signal after receiving the
signal at pin 87 (HSDI).
■ MSK/ DTMF
The demodulated signal from the FM IC (IC500) will
input to the baseband IC(IC701), then the baseband IC will
decode and send the decoded information to the MCU by
the data line.
The MCU then processes the decoded information.
IC701
Baseband IC
IC500
FM IC
DTMF/MSK
decode
Fig. 15 Decode
14
V
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CIRCUIT DESCRIPTION
REPLAY data
DTMF/MSK
decode data
IC702
LSDI
MCU
QT/DQT
HSDO
2-TONE
SB
Q707
IGN
SW
SBC
5M
BATT
POWER
3.3M
IC702
MCU
POWER
SW
Fig. 16 Power supply circuit
7. Power Supply Circuit
When the power switch on the display unit is pressed,
the power port on the display unit which is connected to
port 17 (POWER), goes low, then port 52 (SBC) goes high,
Q719 turns on, SB switch (Q720) turns on and power (SB) is
supplied to the transceiver.
When the DC power is supplied to the transceiver, the
voltage regulator IC (IC707, IC706) and supply into the MCU
VDD and reset the voltage detect IC (IC709). IC709 will
generate signal (RESET) into the reset terminal on the MCU
(IC702) to carry out a power on reset. Also, MCU (IC702) is
checking on port 91 (BATT). If DC power is less than about
8.5V, the transceiver is unable to power on.
When the DC power voltage deceases from normal volt-
age, the INT voltage detector IC (IC708) will set to high on
MCU port 18 (INT). If B line becomes less than about 8.5V,
MCU will send the backup data to EEPROM (IC703) and go
into STOP mode.
This circuit has an overvoltage protection circuit. If a DC
voltage of 16V or higher is applied to the base of Q710, this
voltage turns Q710 on and sets port 18 (INT) to low. As a re-
sult port 78 (SBC) is low, and turns Q719 and Q720 (SB) off.
Q720
SW
Q719
SW
IC707
AVR
D715
IC706 Q710
AVR SW
IC709
AVR
IC708
AVR
B