Kenwood TK-7160 Service Manual page 16

TK-7160
■ Decode
The signal goes to EXTLIMIN (pin 5) of AQUA IC (IC241).
The QT/DQT signal will pass through the low-pass filters in
the AQUA IC (IC241) and be decoded within the AQUA IC
(IC241). The DTMF signal will be decoded within the AQUA
IC (IC241).
IC241
AQUA IC
EXTLIMIN
Fig. 15 Decode
■ D/A Converter
The D/A converter (IC201) is used to adjust MO modula-
tion, AF volume, TV voltage, FC reference voltage, and PC
POWER CONTROL voltage level.
Adjustment values are sent from the CPU as serial data.
The D/A converter has a resolution of 256 and the following
relationship is valid:
D/A output = (Vin – VDAref) / 256 x n + VDAref
Vin: Analog input
VDAref: D/A reference voltage
n: Serial data value from the microprocessor (CPU)
16
CIRCUIT DESCRIPTION
5
SB
Q84
IGN
SW
SBC
IC101
CPU
5M
BATT
POWER
POWER
SW
Fig. 16 Power supply circuit
Power Supply Circuit
When the power switch on the display unit is pressed, the
power port on the display unit which is connected port 17
(POWER), goes low, then port 78 (SBC) goes high, Q42 turns
on, SB SW (Q41) turns on and power (SB) is supplied to the
radio.
When the DC power supplied to the radio, the voltage
regulator IC (IC43) supply into the CPU VDD and reset voltage
detect IC (IC44). IC44 will generate signal (RESET) in to the
reset terminal on the CPU (IC101) to carry out a power ON
reset. Also, CPU (IC101) is checking on port 91 (BATT). If DC
power is less than about 9.5V, the radio is unable to power
on.
When the DC power voltage deceases from normal volt-
age, the INT voltage detector IC (IC45) will set to high on CPU
port 18 (INT) if B line will became less than about 9.5V. Then
CPU send to EEPROM (IC81) the backup data 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 Q81, this
voltage turns Q81 on and sets port 18 (INT) to low. As a
result port 78 (SBC) is low, and turns Q42 and Q41 (SB) off.
Q41
SW
Q42
SW
D81
Q81
SW
5M
IC43
AVR
IC44
RST
IC45
AVR
B