Kenwood TK-7100 Service Manual page 21

■ Decode
• QT/DQT/DTMF
The signal (W/NO (EVOL2)) goes to SIGNAL (pin 88) of
CPU (IC101). The QT/DQT signal will pass through the low-
pass filters in the CPU (IC101) and be decoded within the
CPU (IC101). The DTMF signal will be decoded within the
CPU (IC101).
IC101
CPU
88
SIGNAL
Fig. 15 Decode
■ D/A Converter
The D/A converter (IC161) 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)
CIRCUIT DESCRIPTION
W/NO (EVOL2)
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 82 (SBC) goes high, Q32 turns
on, SB SW (Q31) turns on and power (SB) is supplied to the
radio.
When the DC power supplied to the radio, the voltage
regulator IC (IC33) supply into the CPU VDD and reset voltage
detect IC (IC34). IC34 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 (Battery Volt-
age). 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 (IC35) will set to high on CPU
port 18 (INT) if B line will became less than about 9.5V. Then
CPU send to EEPROM (IC66) the backup data and go into
STOP mode.
This circuit has an overvoltage protection circuit. If a DC
voltage of 18V or higher is applied to the base of Q61, this
voltage turns Q61 on and turns Q32 and SB off.
SB
Q71
IGN
SW
SBC
IC101
CPU
5M
BATT
POWER
POWER
SW
Fig. 16 Power supply circuit
TK-7100
Q31
B
SW
Q32
SW
D61
Q61
SW
5M
IC33
AVR
IC34
RST
IC35
AVR
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