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be determined with audio output: otherwise, the
overload circuit will be activated upon reception of
audio.
Some of the vehicular equipment listed may re-
quire more than 2 amperes of load current. This is
especially true of transceivers during the trans-
mitting mode and some tape players in the track
change mode. If you have only occasional need to
service such equipment, another power supply is
not necessarily required. A vehicular battery of the
correct voltage and of sufficient capacity will suffice.
During testing, the transmitter does not normally
need to be keyed except for short periods. The bat-
tery will provide adequate power for such testing.
The power supply can be used as a battery charger
to restore the battery to full charge, and all non-
transmit testing can be done using the power supply
as the dc power source.
Refer to Figure 4. Although it is Possible to obtain
up to 4 amperes load current from two power sup
POWER SUPPLY
Set CURRENT LIMIT
specification
to
for module being
serviced.
Figure 5. Typical Power Supply
plies connected in parallel, it is not recommended
except for use by highly experienced personnel.
The power supplies should not be connected directly
in parallel, but should be isolated by very low re-
sistance so that balance is not so critical. Even with
this technique, the power supplies must be well
balanced or the unit carrying the heavier load will
overload and turn off, which, in turn, will cause the
other Power supply to overload and turn off. It is
very difficult to bring the power supply output of
both units up to operating voltage without disturb-
ing the balance. One method to achieve balance is
to use an external switching arrangement which
allows selection of the load or a dummy load. The
dummy load should be selected to draw approx-
imately 1 ampere at the operating voltage of the
main load: ½ ampere from each power supply. The
Power supplies can be accurately balanced into the
to the main load.
SERVICING PLUG-IN MODULES
Equipment containing plug-in modules is often
repaired by replacing a malfunctioning module.
then servicing the defective module on the bench.
A dc Power source such as this power supply is re-
Set VOLTAGE to
specification for
module being ser-
viced.
Connection to Module For Bench Testing
quired for bench testing modules. Figure 5 shows a
typical test set-up. Connect the (+) and (-) outputs
of the power supply to the (+) and (-) power ter-
minals of the module. Identical power is sometimes
required at two or more terminals of a module. If
so, jumper together these terminals. An earth
ground may or may not be required. A test hook-up
diagram for bench testing the module should be
obtained. It should specify the operating voltage
and current limit. The current limit will typically be
lower than those previously described for battery
operated and vehicular equipment, since only a
single module is being powered.
Module testing is more likely to require two sep-
arate dc voltages simultaneously. Refer to the next
paragraph for information.
USING TWO POWER SUPPLIES
FOR TWO OUTPUT VOLTAGES
When two separate dc voltages are required
MODULE BEING
SERVICED
simultaneously for testing equipment, two power
supplies may be used. Set the voltage and current
limit for each power supply independently as re-
quired by each circuit. Only the circuit reference
point must be common between the two supplies.
Figure 6 shows some typical examples of proper
power supply connections when using two units.
Take extra precaution to prevent reverse polarity
connections in' such situations. The numerous con-
nections can become confusing. Additional colors
for the test leads will be helpful. The power sup
plies are protected from reverse polarity damage
from an external voltage source (such as the other
power supply).
TWO POWER SUPPLIES IN SERIES
FOR O-100 VOLT OUTPUT
The power supplies may be connected in series
for output voltages over 50 volts at 0 to 2 amperes.
Figure 7 shows the correct connections. Set the
current limit for both supplies at the same value and
equalize the voltage between the two units. Since
both units are connected in series, an overload in
either unit will shut down the output from both
plies, The power supplies are built to permit stack-
ing when two units are used.
sup-
9
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