sets that are moved frequently will develop trouble of this kind at one
time or another. To check the cording, look for opens, shorts, and faulty
contacts. Wiggle the cord at the socket or plug to see if good contact is
being made.
You should also make sure that the correct plug is in the
correct socket and that a snug fit is made.
In some types of aircraft
radio equipment, you may have to make your own connecting cables.
Give
these types of cables a good once-over when making your visual inspection.
(5) Think you've covered everything? --well, not quite. How about looking for
broken tubes or sockets, badly soldered joints, tube socket pins touching
each other, tuning capacitor plates touching each other, or broken slugs
in IF transformer cans? Any of these troubles could cause your set to be
inoperative.
b. Use Your Sense of Smell. Recently burned rubber, paint, or insulation can be
easily recognized by the sharp odor which lingers in the chassis long after the set
is brought in for repair.
Bad selenium rectifiers, caused by overheating, smell
like rotten eggs.
You won't have much trouble recognizing this symptom if it
appears.
NOTE:
Do not make any check that requires power to be turned on, unless
you've checked the key circuits for shorts.
Actually, the key
circuit check is a resistance check which helps locate any short
circuits that might damage the power supply.
This check will also
prevent additional damage to the equipment when power is applied.
c. Use Your Sense of Touch.
In most cases, touching the electron tubes after
the set has been turned on for a couple of minutes will show if the tube filaments
are heated.
Your sense of touch can also be used to check for faulty resistors,
transformers, and capacitors. Just turn on your set for a few minutes, then turn
it off. Cautiously touch the different components and see if any are overheated.
Be careful of capacitors in high-voltage circuits, however. Short them out with a
small jumper wire, after you've turned off the power.
If you've looked over
everything that has been mentioned, you've made a good all-round inspection.
d. Checking Key Circuits for Shorts. The purpose of this check is to make sure
that when you connect power to your receiver or receiver-transmitter there are no
short circuits in the equipment. Actually, this test consists of resistance checks
which help to locate any short circuits that might damage the power supply. This
check will also prevent additional damage to the equipment when power is applied.
In battery-operated equipment, resistance measurements are made from pins of the
battery plug to ground. In other types of power supplies, like the vibrator-type
power supply, resistance measurements are made from the power-in jack to ground.
Use an electronic multimeter like the TS-505/U or its equal. Compare the readings
you get with those listed in the TM. If you don't get the required reading, refer
to the schematic diagram of the receiver to find out which part or parts may be at
fault. Since the key circuit test often indicates trouble in the power supply, the
following information will prove helpful:
322 L5
37
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