Kenwood TM-V708A Service Manual page 9

3-3. APC circuit
The Automatic transmission Power Control (APC) circuit
has a differential amplifier (IC200) that compares the DC
voltage generated by detecting part of the transmission
output using diodes (VHF: D18, D19; UHF: D317, D318) with
VHF
UHF
3-4. Overheating protection circuit
To protect from the thermal destruction of the power
module, the voltage of the thermistor (TH1) near the power
module is monitored by the CPU (IC604). If it becomes high
temperature, the APC voltage is controlled to cool down the
temperature.
4. PLL circuit
4-1. Reference oscillator circuit
The 12.8MHz signal is generated by the crystal oscillator
circuit (IC1 and IC301) and internally divided to generate 5kHz
or 6.25kHz reference frequency. The 12.8MHz signal on IC1
side is tripled by Q102 to obtain the second local oscillator for
the A band. The reference oscillation circuit is also modulated
to improve the modulation characteristics of the DCS and
9600bps packet signal when it is transmitted.
CIRCUIT DESCRIPTION
D18
D19
D317
D318
Fig. 10 APC circuit
the reference voltage output from the CPU. The output signal
is amplified by Q209 and Q208 and fed to the power module
to keep transmission output constant.
DC AMP
COMPARATOR
Q209
IC200
2SC4617
TA75S01F
(R)
CPU
CHARGE PUMP
Q1 2SA1774(S)
Q2 2SC4617(R)
Q102
2SC4649
(N,P)
38.4MHz
CHARGE PUMP
Q300 2SA1774(S)
Q301 2SC4617(R)
Fig. 11 PLL circuit
TM-V708A
DC AMP
Q208
DB
2SB1565
(E,F)
VHF VCO
CV
HT
IC2
KCH38
PLL
Q3
IC1
2SC5108
MB1511PFV-GBND
(Y)
LD
12.8MHz
X3
UHF VCO
CV
HT
IC302
KCH28
PLL
Q304
IC301
2SC5108
MB1511PFV-GBND
(Y)
LD
12.8MHz
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