Kenwood TKR-D710 Service Manual page 16

TKR-D710
3-2. CM coupler circuit
The CM coupler circuit is a line for detecting forward
wave and refl ected wave. Forward wave is detected by D3,
and is converted into DC voltage. If an abnormal antenna
load is connected, reflected wave is detected by D4 and
converted into DC voltage.
3-3. Filter circuit
This circuit removes harmonics from the transmitter out-
put and sends fi ltered signals to the antenna.
3-4. APC circuit
The automatic transmission power control (APC) circuit
stabilizers the transmitter output power at a pre-determined
level. DC voltage from the CM coupler circuit is amplifi ed by
the DC amplifi er IC202 (1/2). IC202 (2/2) compares the APC
control voltage (RAMP) generated by the MCU (X53-458)
and the DC amplifi er IC201 (1/2, 2/2) with the output voltage
from IC202 (1/2) to control the gate voltage for amplifi er Q3
and fi nal amplifi er Q4.
3-5. High temperature detector circuit
To prevent thermal destruction of amplifi er Q3 and fi nal
amplifier Q4, this circuit reduces the APC control voltage
(RAMP) when the temperature of amplifi er Q3 and fi nal am-
plifi er Q4 rises. The MCU detects the temperature with the
thermistor (TH201) and controls the APC voltage (RAMP).
4. Control unit
The Control unit (X53-458) consists of the following cir-
cuits:
(1) MCU circuit
(2) Memory circuit
(3) DSP circuit
(4) Squelch circuit
(5) Power supply circuit
(6) Power Supply Voltage Monitoring Circuit
(7) 18.432MHz clock circuit
(8) Audio circuit
(9) Other circuit
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CIRCUIT DESCRIPTION
CN201
+B
from Final unit
(X45-401 B/3)
CN203
+B
to TX-RX unit
(X57-894)
Fig. 13 AVR circuit
3-6. FAN action control circuit
The FAN action control circuit consists of the FAN and
switching transistor Q207 . It is controlled by the MCU (X53-
458). If the FAN action is set to "Temperature" , the cooling
fan is turned ON or OFF according to temperature. If the
FAN action is set to "Continuous" , the cooling fan operates
continuously, but Q207 stays ON.
3-7. AVR circuit
The power source (+B) is provided through connector
CN201 to the Final unit (X45-401 A/3). +B is connected to
CN203 to supply the 13.6V power source for the TX-RX
unit (X57-894). +B is a power source for the "final ampli-
fi er" , "drive amplifi er" and fan. IC203 regulates the +B volt-
age to 8V. This 8V power source is connected to the FET
switches Q203, Q204, Q205, and Q206. Q204 and Q206
are controlled by the "8TC" signal from the I/O expander IC
which is in the TX-RX unit (X57-894). If "8TC" logic is high,
Q204 and Q206 turn on and supply the 8V power source
to the APC circuit and pre drive amplifi ers. Q203 and Q205
are controlled by the "ASWC" signal from the I/O expander
IC which is in the TX-RX unit (X57-894). If "ASWC" logic
is high, Q203 and Q205 turn on and supply the 8V power
source to the antenna switch circuit.
Final AMP
Drive AMP
FAB
IC203 Q204,Q206
8V AVR SW 80T
8TC
Q203,Q205
SW 80SW
ASWC
4-1. MCU circuit
The MCU (IC20) is a 32bit RISC processor, equipped with
a peripheral function and ADC/DAC.
This MCU operates at a 18.432MHz clock and 3.3V/1.5V
DC.
It controls the fl ash memory, SRAM, DSP , receive circuit,
transmitter circuit, and control circuit.