Icom IC-2GA Service Manual

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 ІС503 (pin 52) becomes "HIGH," the
S/RF level, calculated from the delay time, is displayed.
А/О! A/DO
ву (IC503 PIN51) _ (IC503 PIN52) S/RF signal
C507 C511
(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)
+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 1С202 (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 ІС503 sends power save data
to 12202.
SQL LOW
BEEP OFF POWER
1 1C202
2 SHIFT
3 REGISTER
РЭС TMUT
STANDBY STANDBY
SHUT- SHUT- SHUT-
DOWN DOWN DOWN
^ 500 " T 500 ` ` 500
msec msec msec
125 125
msec msec
Using this data, 12202 (ріп 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 O211 and Q213 — 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 IC601's dividing
ratio based on 6-bit data from 1С503. А 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 Q218. A
voltage is applied to IC206. 1C206 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+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. Q801
is turned on for about one second to maintain transmission
without pushing the PTT switch.

Icom IC-2GA Specifications

General

Brand	Icom
Model	IC-2GA
Category	Transceiver
Language	English