Icom IC-T7A Service Manual

4-3-2
UHFPLL CIRCUIT (1F UNIT)
The oscillated signal at the VCO circuit (DUAL VCO
board
Q301, Q302,
D301)
is amplified at a buffer-amplifier
(Q306)
and is
again amplified at another buffer-amplifier
(Q352).
The
amplified signal is applied to the PLL IC
(IC851
pin
19),
and
then divided by serial data from the
CPU. It is the
phase-detected
with
the
divided reference
frequency and
the phase difference is output as pulses.
The output signals
from
IC851
(pin
13)
are converted to
DC
voltages (lock voltage) by the loop filter (R866,
C862)
and
are
then fed back to the UHF VCO circuit
to stabilize the
VCO
frequency.
4-4
POWER SUPPLY CIRCUITS
VOLTAGE
LINE
Line Description
HV
The
voltage
from the external power
supply or
attached battery pack.
VCC
The same voltage as
the HV line (external
power supply or battery
pack) which is
controlled by the power switch
([POWER]
control).
+3CPU
Common
3 V
converted
from the
VCC line by
the +3CPU regulator
IC (LOGIC
unit
IC2).
The
output voltage
is supplied
to the
+3C,
R3
and
T4
regulator circuits,
etc.
+3C
Common
3
V converted
from the VCC
line by
the
+3C
regulator circuit
(LOGIC unit
Q4,
Q5)
using the +3CPU regulator
(LOGIC unit
IC2).
R3
3
V for receiver circuit converted
from
the VCC
line
by
the
R3 regulator circuit (2F
unit
04, 05).
T4
4 V for transmitter circuit
converted from
the
VCC line by the T4 regulator
circuit (1 F unit
0702, 0703).
The T4
regulator circuit
controlled by the CPU
(LOGIC unit IC1 pin
45)
via
T4
control
regulator circuit
(1 F unit
0704).
T8
8
V for drive amplifier
circuit converted
from the
VCC line by
the T8 regulator circuit
(1 F unit
01
00,
01
01,
D100).
4-5
OTHER CIRCUITS
4-5-1
TONE SQUELCH CIRCUIT
(LOGIC
UNIT)
A
portion
of the detected audio signals from
the “DETO”
line
are passed through
the
low-pass
filter (IC13). The
filtered
signal is then applied
to the CPU (IC1 pin
4),
and is
compared
with the programmed
tone signal. The
CPU
(IC1) outputs control signals
to the AF mute
and AF
regulator
circuits to open the squelch
when a matched tone
signal is received.
The programmed
subaudible
tone signal is output from
the
CPU
(LOGIC unit IC1 pin
9)
directly when
transmitting with
a tone.
4-4

Icom IC-T7A Specifications

General

Brand	Icom
Model	IC-T7A
Category	Transceiver
Language	English