TM 11-5826-225-35
Procedure
Probable trouble
Indication
Item
I
Check transistors (fig. 23).
Audio amplifier Q12, Q13, or
Q14 defective.
Control unit LOOP switch Loss of 110-CPS reference
See item 15.
phase voltage on resolver
rotates bearing indica-
tor pointer in one direc-
servo motor B5.
tion only.
(4) L i s t e n f o r a u d i o o u t p u t s i g n a l i n
2-6. S i g n a l S u b s t i t u t i o n
headset. If. no signal is heard, check
a. General. S i g n a l s u b s t i t u t i o n p r o c e d u r e s
audio output transformer T20 and
help to localize trouble to a stage in the re-
capacitor C78.
ceiver. An externally generated signal is sub-
(5) Set audio oscillator output signal level
stituted for the signal normally present in each
to 850 millivolts and apply signal to
stage. The test equipment required for the
the collector of Q13. Audio output
tests in b through d below is listed in para-
from the headset should be as loud as
graph 2-3e. In the following tests, ground one
obtained in (4) above. If no sound
side of the audio oscillator or signal generator
is heard or output is low, check tran-
to the receiver chassis and conned the output
sistor Q14 and associated base signal
lead to the receiver test point indicated. When
input circuitry.
performing these tests, use the receiver main
(6) Set audio oscillator output signal to
schematic diagram (fig. 5-10 or 5-10.1.) in
33 millivolts and apply signal to the
conjunction with the parts location
base of Q13. Sound output should be
illustrations referenced in the following
procedures.
equal to that obtained in (4). If no
Caution: All circuits in the receiver are
sound is heard or sound level is weak,
transistorized. To avoid transistor damage, use
check transistor Q 13 and associated
tape or sleeving to cover the test leads except
circuit components.
for the extreme end required for testing,
(7) Adjust audio oscillator for an output
b. Audiofrequency Tests. Start these tests
of 42 millivolts and apply signal to
at the output of the last audio amplifier stage
the base of transistor Q12. Sound out-
and work back toward the first stage (figs.
put in headset should he equal to that
obtained in (4). If not, check transis-
fully clockwise.
tor Q12 and associated circuit com-
(1) Connect the receiver to Test Set, Di-
ponents.
rection Finder Set AN/ARM93 as
Note. After making the above tests, adjust
the variable resistor R82 in accordance with
shown in figure 22, but do not con-
the instructions in paragraph 3-17.
nect RF Signal Generator AN/URM
Tests. Start
the
25. Set the test set and control unit
c.
Intermediate
tests at the output of the last IF amplifier
controls as indicated in paragraph
stage and work back toward the first IF stage
2-5c. The range switch and TUNE
control may be set in any position.
resistor R90 (fig. 2-8) fully clockwise.
(2) Set Audio Oscillator TS-382/U to pro-
duce an audio output signal of 400
(1) Use the test setup described in p a r a -
graph 26b (1).
cycles at 5 volts rms.
(3) Using a 10-microfarad capacitor in
(2) Set RF Signal Generator A N / U R M - -
series with the audio oscillator out-
25 for a 142.5-kc output signal mod-
put lead, connect lead to the collector
ulated 30 percent at 400 cps. Adjust
of audio amplifier Q14.
output signal level to 50 millivolts.
2-22 Change 1
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