Icom IC-280E Instruction Manual page 17

The pulse signals are put out at RO-R2 of the CPU т order, synchronizing with the 7-segment
display data outputs 01-07 and O1-O3 are turned ON Бу these pulse signals. O1 is for the 1MHz
LED, Q2 is for the 100KHz LED and Q3 is for the 10KHz LED. When the power is turned ON,
O4 is turned ON and the display operation becomes possible. Q1 is turned ON by the RO signal,
and 7-segment signals (O1-O7) are fed to 1С12 for the 1MHz display. The same data is converted
to BCD, 2 is subtracted and put out at R7-R9 of the CPU. Then Q2 is turned ON by the R1 signal
and 7-segment signals (O1-O7) are fed to IC13 for the 100KHz display. The same data is
converted to BCD and put out at RO-R3 of the CPU. The output signals at the RO-R3 are latched
by IC8 and R6 signal is used as its clock.
ОЗ is turned ON by the R2 signal and the 7-segment signals (O1-O7) are fed to 1С14 for the
10KHz display. The same data is converted to BCD, 2 is added to this and put out at RO-R3. The
output signals at RO-R3 are latched by IC9 and the R5 signal is used as its clock.
O4 and Q5 function as a flip-flop to prevent the latched data 00-03 from being fed to the display.
The 5KHz display LED is illuminated and the 5KHz step operation is made possible by setting R4
of the CPU to L-level. |
MIC AMP and AUDIO AMP
Dual low-noise op. amp 1С11 functions as both а mic amplifier and a limiter audio IC. 1C10 has a
high power output (2W or more at 8 ohm load) with low distortion and various protection circuits
built in. Q14 is turned ON during the transmit mode to mute !C10.
Power Supply Circuit
IC-280E has a specially designed voltage regulator to prevent the CPU and others from mal-
functions caused by voltage fluctuation.
When 13.8V is supplied to the cathode of Zener diode 06 (Zener voltage 9.2V), 010 is turned ON
and the level at the base of Q9 becomes the ground level, so that O9 also is turned ON. By this
operation, the current drains through 05 and charges C4. СЗ is charged by the memory power УМ.
Which is supplied to the cathode of 05 from the main unit, the base current drains through Об
and Об is turned ON. The collector output voltage of Об is divided by R26 and R27, and.is fed
to the base of O7, which is thus turned ON. Approximately 0.6V lower than the voltage at the
base of O7 (approximately 3.5V) is supplied at the emitter, so that the voltage at the cathode of
the 5.5V Zener D4 become 9V (3.5V+5.5V). When the voltage at the cathode of D4 varies, the
emitter voltage of Q7 varies, the base current is thus varied, and then the collector current (which
is also the base current of Q6) is varied. In this way, O6 is controlled for the regulating operation.
When the voltage of the power supply drops suddenly to below about 10V, D6 is turned OFF and
the continuous pulse signal from ВЗ of the CPU is fed to the base of Q10. By this pulse signal,
repeatedly turns Q10 ON and OFF, so that O8 and O9 repeatedly turn ON and OFF simul-
taneously. This operation charges C4 and the doubled voltage is supplied to the emitter of Об.
TONE CALL UNIT
This unit produces a tone-burst for accessing a repeater. If the Tone Call Button is depressed
during transmission, the circuit is actuated, and a multivibrator, IC1 generates a tone-burst of
1750Hz. The tone-burst frequency can be adjusted by R2 and output level of the circuit can be
adjusted by R4. Output of the circuit is supplied to the low-pass filter, Q13.
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