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If the terminals have polarity, Бе sure to make the correct
connection.
Note that the keyed voltage when switching
with semiconductors or relays with resistors in the circuit,
should be adjusted to be below 0.4 Volts!
3-9
RTTY
When
operating
RTTY,
connect the ACC
socket pins 8
(ground) and 9 to your tele-typewriter through a high speed
relay or a level converter to TTL level, and the tones for
your terminal unit will be available from pin 4. The AF
output level is about 300mV P-P for 5-9 signal.
For details,
refer to
5-4 RTTY OPERATION
on page 18.
3-10
EXTERNAL
SPEAKER
The ІС-720А contains an internal speaker, and is also
designed so:that it can drive an external speaker from the
external (EXT) speaker jack on the rear panel.
Be sure the
impedance of the external speaker is 8 ohms, and remember
that
with
the
external
speaker
connected,
the
internal
speaker is disabled.
3-11
HEADPHONES
7
Any good headphone set, including stereo type, that have
4-16 ohms impedance can be used.
With the plug inserted
halfway into the PHONES jack, both the headphone and
speaker will operate.
This is convenient when others wish
to listen in on the station, or you wish to record contacts
using a tape recorder
connected
to the headphone jack.
With
a stereo
headphone set inserted this way, however,
the headphone will lose the sound on one side.
With the
plug inserted completely, only the headphone works.
3-12
COOLING
FAN
The rear of the PA unit is designed to provide for adequate
cooling, but with 200 Watts input the final stage produces
quite a bit of heat, and its temperature
may rise during
prolonged transmissions.
The fan is connected
to a tem-
perature monitoring circuit which monitors the temperature
of the final stage. The fan operates as follows:
1. The fan does not operate in the receive mode, but will
run all the time in transmit.
. When
the temperature
rises to a point detected by the
monitor curcuit the fan will operate during both transmit
and receive to provide additional cooling.
. If the temperature rises їо a danger limit the fan will run
much more rapidly.
At this time stop transmitting and
investigate
the cause
of overheating
i.e. antenna
mis-
match, etc.
Correct the cause of the overheating before
starting to transmit again.
3-13
POWER
SUPPLY
It is recommended
that you use the IC-PS15 as a power
supply for base operation.
If you wish to use another type
power supply make sure that it meets the voltage, current
requirements.
Note carefully the overvoltage protection,
for a runaway regulator can destroy the ІС-720А; be espe-
cially careful that more than 16 Volts cannot be supplied to
the transceiver.
Do not connect the power supply, antenna,
accessory
plug, or microphone
with the Power Switch
in
the ON position.
Be especially careful not to transmit with-
out
an antenna
or dummy
load hooked
up.
If the fuse
blows replace it with a 20 Amp fuse, only after fixing the
cause.
Do not turn the Power Switch ON and OFF Тереа!-
edly for this way cause the readout to mis-display.
Should
this occur, turn the set OFF and wait for approximately 30
seconds before turning it back ON.
3-14
CAUTIONS
As the unit has already been closely adjusted with highly
sophisticated measuring instruments, never tamper with the
turnable resistors, coils, trimmers, etc.
C-MOS is used in the Logic unit as well as the PLL. C-MOS
ICs are very susceptible to excessive static charges and over-
current and care must be used when handling them.
There-
fore, avoid touching the Logic unit and the nearby circuitry
unless absolutely necessary.
When it is necessary to check
the circuitry, observe the following points.
Ground
а! measuring instruments, the soldering iron, and
other tools.
Do not connect or disconnect the C-MOS IC
from its socket, or solder it when the power is on.
Do not
apply voltage of less than —0.5 or more than +5 Volts to
the input terminals of the 1С.
DO NOT MEASURE WITH
AN OHMMETER.
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