Icom IC-2GA Service Manual page 13

4-5 OTHER
CIRCUITS
(1)
S/RF
METER
CIRCUIT (LOGIC UNIT)
The
voltages detected
at
the
S-meter detector (Q4, Q5, D7)
or the
APC
detector (D13,
D14) are applied to pin 2 of IC502
(1/2).
When
the voltage
level
is
detected,
IC503
(pin 52)
outputs
a
"'HIGH"
signal.
Because
the
signal
passes
through an
integrator circuit
(C507, R517), the voltage
at
pin
3 increases with time.
When
the voltage
at
pin 3
is
greater
than
that at
pin
2,
pin
1
outputs
a
"HIGH"
signal to
IC503 (pin
51).
When
IC503
(pin
52)
becomes "HIGH,"
the
S/RF
level,
calculated
from the delay time,
is
displayed.
a/di
a/do
(2)
LAMP
CIRCUIT (LOGIC UNIT)
When
the
LIGHT
SWITCH
Is
pushed,
the IC503
(pin 53)
LAMP
signal
becomes
"HIGH."
The
current of
this
signal
is
amplified
at
Q501
to light
the
two
chip-type
LED
(DS502,
DS503).
(3)
LOW
VOLTAGE DETECTOR
CIRCUIT
(LOGIC UNIT)
-I-5S
is
divided
over
R523 and
R524. 1.16
V
are applied to
IC502B
(pin
5).
The Vcc voltage, divided
over
R525 and
R526,
is
applied to pin
6.
When
the
Vcc
voltage
exceeds
5.7 V,
the voltage
at pin
6
becomes
greater
than that
at
pin
5.
Output
pin
1
becomes "LOW."
When
the Vcc voltage
is
less
than 5.7 V,
the voltage
at
pin 5
exceeds
that at pin
6.
Pin
1
outputs "HIGH."
The
TRANSMIT INDICATOR
does not
light
even
when
transmitting.
(4)
BEEP CIRCUIT
(MAIN
UNIT)
When some
switches are
pushed, the
CPU
sends
BEEP
data
to IC102.
Beep
tones are
output
from
IC202 (pin
5)
in
square
waves
of
about
1
kHz and 500
Hz.
(5)
POWER
SAVER
CIRCUIT
(MAIN
UNIT)
When
the squelch
Is
closed, IC503
(pin 41)
BUSY
signal
is
"LOW."
If
no operation
is
performed
for
more
than 30
seconds, the
power
save function
is
automatically
acti-
vated. After
30 seconds, the IC503
sends
power
save data
to IC202.
SQL
LOW
Using
this data,
IC202 (pin 12)
alternately
outputs
"HIGH"
(shut-down)
for
500 msec, and
"LOW"
(standby) for
125
msec. This output, applied to
IC203D
(pins
5
and
6)
and
IC023C
(pin
9),
controls the
bases
of
021
1
and
0213
—
thus
controlling
+5S and R+5.
If
a signal
is
received, the
BUSY
signal
becomes
"HIGH,"
shutting off
the
power
save function.
If
a signal
is
not
received,
"HIGH" and
"LOW"
signals
continue to alternate.
(6)
SUBAUDIBLE
TONE ENCODER
(IC-2GA,
IC-2GAT)
When
the
tone encoder
is
turned
on, the X601 reference
frequency (3.579545
MHz)
is
divided
by IC60Vs
dividing
ratio
based
on
6-bit
data
from
IC503.
A
tone
(67.0
Hz~250.3
Hz)
is
output
from
pin
1.
The
tone output
passes through R601
for
deviation
adjustment
and
is
supplied to the
MAIN
UNIT.
(7)
TONE
CALL
(IC-2GE)
Pushing
the
TONE CALL SWITCH
(S206) turns
on 0218.
A
voltage
is
applied to IC206.
IC206 divides 7.168
MHz
by
4,096;
and outputs
a
1750 Hz tone through pin
4.
R242
provides deviation adjustment.
(8)
DTMF ENCODER
(IC-2GAT)
IC801
generates
DTMF
tone signals.
When
transmitting,
T-i-5
V
are applied to IC801 (pins
1
and
2).
If,
at
this
time,
data are entered with the keypad, the
frequency
(3.58
MHz)
oscillated
by X801
is
divided
by the appropriate dividing
ratio.
Pin 17
outputs audio frequencies
coresponding
to
ROW
and
COL
input.
R801 provides deviation
adjustment.
When
a
key
is
pushed,
a
"HIGH"
signal
is
output to pin
11.
0801
is
turned on
for
about one second
to
maintain transmission
without pushing the
PTT
switch.
4-4