Icom IC-W2A Service Manual page 10

3-5-2
VHF
CHARGE PUMP AND LOOP
FILTER
CIRCUITS (VHF
RF
UNIT)
Phase-detected
signals
from IC8 are converted
to
DC
voltage
by a constant-current
circuit
(Q17~19) and
a lag-loop
filter
to
control
the
VCO
oscillating signals.
The PLL
lock
voltage
changes
the
reactance
of
varactor
diodes
in
the
VCO
circuit.
The
DC
voltage
of
the
VHF
PLL
is
also
used
for
the receiver
tuning circuit
on
the
VRF A
UNIT.
3-5-3
UHF
CHARGE PUMP AND LOOP
FILTER
CIRCUITS (UHF
RF
UNIT)
Phase-detected
signals
from IC6 are converted
to
DC
voltage
by a
constant-current
circuit (Q12,
Q13, Q31) and
a lag-loop
filter
to control
the
VCO
oscillating signals.
The PLL
lock
voltage
changes
the
reactance
of
varactor
diodes
in
the
VCO
circuit.
3-5-4
VHF
VCO
CIRCUIT (VHF
RF
UNIT)
The
VCO
circuit oscillates
the
PLL
output
frequency
control-
ling
varactor diodes.
DIO, a
varactor diode, provides the
frequency
control.
The
control signal
from ICS
(pin 6)
turns
Q42
ON
or
OFF
to
switch
the
VCO
frequency
between
transmission
and
reception.
3-5-5
UHF
VCO
CIRCUIT
(V
VCO
UNIT)
D1, a varactor diode,
provides the frequency
control.
The
control signal
from ICS
(pin
6)
turns
014
ON
or
OFF
to
switch
the
VCO
frequency
between
transmission
and
reception.
3-6-3
VOLTAGE
LINES
LINE
DESCRIPTION
VCC
This voltage
is
supplied
from a
battery
pack
or
external
DC
power
supply.
L-T5M
VHF
band
common
5
V
converted from the
VCC
at
Q27 and Q28 on
the
VHF
RF
UNIT.
LR5S
VHF
band
receive 5
V
controlled
by
the
power
saver
function
and
LSEND
signal
line.
This
voltage
is
converted from the
VCC
at
Q29 and
Q30
on
the
VHF RF
UNIT.
L-I-5S
VHF
band
5
V
controlled
by
the
power
saver
function.
This voltage
is
converted from the
VCC
at
Q31 and
Q32 on
the
VHF RF
UNIT.
LT5
VHF
band
transmit
5
V
controlled
by the
LTMT
signal
line.
This voltage
is
converted from
the
VCC
at
Q33 and Q34 on
the
VHF RF
UNIT.
H-I-5M
UHF
band
common
5
V
converted from the
VCC
at
Q16
and
Q17
on
the
UHF RF
UNIT.
HR5S UHF
band
receive 5
V
controlled by the
power
saver function
and
HSEND
signal
line.
This
voltage
is
converted from the
VCC
at
Q18
and
Q19on
the
UHF RF
UNIT.
H-I-5S
UHF
band
5
V
controlled
by
the
power
saver
function.
This voltage
is
converted from
the
VCC
at
Q20
and
Q21 on
the
UHF
RF
UNIT.
HT5
UHF
band
transmit 5
V
controlled
by the
HTMT
signal
line.
This voltage
is
converted from
VCC
at
Q22
and
Q23
on
the
UHF RF
UNIT.
3-6
OTHER
CIRCUITS
3-6-1
BATTERY CHARGING
CIRCUIT (PRT
UNIT)
The
transceiver
has a constant-current regulated
circuit for
charging the
connected
battery
pack. This
circuit
charges
the
battery
pack
for
about 15 hours.
The
voltage
from the external
power
supply
is
divided
at
D6,
R6
and R8. This voltage
is
then applied
to
02.
02
controls
01
,
and
the external
power
supply
charges the battery pack.
3-6-2
S-METER
CIRCUIT
(VHF
AND
UHF RF
UNITS)
The S-meter
signal
(VHF;
"LSD"
line,
UHF: "HSD"
line)
from
the
VHF/UHF RF UNIT
is
applied to
the
meter comparator
(VHF:
IC9, pin
3;
UHF:
IC8, pin
3).
Pin
2
of
the
meter
comparator receives
a reference signal
from the
CPU. The
counting
signal
is
increased step
by
step.
Pin
1
is
"HIGH"
when
a reference
signal
is
lower than the
S-meter
signal
and becomes
"LOW"
when
a
reference signal
is
higher
than
the
S-meter
signal.
Pin
1
is
applied
to
the
CPU
(IC1
or IC2).
3
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4