Power Supply Circuits; Other Circuits - 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