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Section II. POWER DISTRIBUTION AND SELF-TEST
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TM-9-4931-363-14-P Fire Control Subsystem Test Set AN/GSM-249 P/N 2201736-05 Manual
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Figure 2-2. Test set self-test functional diagram (sheat 1 of 4)
TM 9-4931-363-14&P
on printed circuit card A2 and is routed through XA2-25
2-4. Self-Test Theory.
and through CR3 to energize relay K3. Contacts 1 and 2 of
a. To prepare for the self-test theory discussion, refer to
energized K3 apply a 28-volt ground to indicators DS14
through DS17. Pressing S11 connects +28 volts through
the test set self-test functional diagram (fig. 2-2) and to the
wiper 1 and contact 9 of S4-B to energize K5 and K7, and
test set self-test table (table 3-3). Refer to paragraph 3-5
through CR24 to provide a logic high at XA2-33. With
and mentally perform steps a, b, and c.
XA2-31 open, the high activates the logic on card A2 to
b. Refer to step 1 in figure 2-2 and in table 3-3.
cause Q5 to provide a ground at XA2-27. A ground at
XA2-27 lights DS7 because DS7-2 is connected to +28
Mentally perform step 1 of table 3-3. POWER indicator
volts. Indicators DS1 through DS6 znd DS8 through DS13
DS18 lights as described in paragraph 2-3.
are connected to +28 volts. Energized contacts 1 and 2 of
c. Mentally perform step 2 of table 3-3 and refer to step
K5 connect +5 volts from XA12-32 through XA2-4 to the
2 in figure 2-2. Wiper 1 and contacts 2 through 9 of S4-C
seven resistor and diode pairs shown in figure 2-2 and in
foldout FO-3. The +5 volts turns on transistors Q2 through
apply 115 volts ac to the primary of T3. The secondary of
Q7 to provide grounds to light indicators DS1 through DS6.
T3 couples 10 volts ac rms to XA2-17 and -18. (Refer to
Energized contacts 5 and 4 of K5 provide grounds to light
foldout FO-3.) The full-wave rectifier consisting of CR4
indicators DS8 through DS12. Energized contacts 1 and 2
through CR7 provides pulsating dc to input pin 1 of 8-volt
of K7 connect +5 volts from XA12-32 to XA2-29, through
regulator AR4. Pin 3 is the return and pin 2 is the output.
the diode and resistor pair on card A2, and through XA2-24
Capacitors C4, C5, and C6 provide filtering. Note that the
power supply is floating. Refer to figure 2-2, step 2. XA2-7
to turn on Q1, which provides a ground to light DS13.
Contacts 4 and 5 of energized K7 connect +28 volts
is connected through TB1-2 to the multimeter, where it is
through XA2-19 and through diodes CR22 through CR25
grounded. The ground at AR4-2 causes the regulator to
on card A2 to light indicators DS14 through DS17. POWER
provide -8 volts dc through XA2-16 and TB1-1 to energize
indicator DS18 lights as soon as power is turned on.
the multimeter. Contacts 2 through 11 and wiper 1 of S3-L
connect the ac voltages shown on figure 2-2 through
h. Mentally perform step 7 of table 3-3. Refer to step 7
contact 3 and wiper 1 of S4-I and through contacts 2 and 3
of figure 2-2. Contact 2 and wiper 1 of S3-L connect 10
of S9 to contacts 2 and 8 of S5-A. Wiper 1 of S5-A
volts ac, phase angle 0 degrees, through contact 3 and wiper
connects each voltage through TB1-3 to the input of the
1 of S4-I, through contacts 2 and 3 of S9, and through
multimeter for readout. Wiper 2 of S5-A connects each
contact 8 and wiper 2 of S5-A to XA2-41 of phase detector
voltage to XA2-41 for phase determination.
card A2. The 10 volts ac, phase angle 0 degrees is also
d. Mentally perform step 3 of table 3-3 and refer to step
connected to XA2-34.
3 in figure 2-2. Contact 8 and wiper 2 of S7-F connect +28
volts dc through contact 3 and wiper 1 of S8-L and through
(l) Refer to foldout FO-3. The circuitry associated
S5-A and TB1-3 to the meter input for readout.
with PNP transistor Q4 and FET Q2 comprise a chopper
which opens and closes the in-phase input at amplifier
e. Mentally perform step 4 of table 3-3 and refer to step
AR2-3. XA2-34 is connected to in-phase 10 volts ac, which
4 in figure 2-2. Wiper 1 and contacts 2 through 6 of S7-F
becomes a reference for signals inserted for phase detection
connect the dc voltages shown on figure 2-2 through
at XA2-41. The positive part of the reference signal from
contact 2 and wiper 1 of S8-L, through contact 6 and wiper
XA2-34 (fig. 2-1, waveform A) is conducted to ground
1 of S5-A, and through TB1-3 to the input of the
through R11 and CR3. The drop across the junction of
multimeter for readout.
CR3 leaves Q4-B (waveform B) at +0.7 volt, which turns
the transistor off, causing Q4C (waveform C) to go to -6
f. Mentally perform step 5 of table 3-3 and refer to step
volts through R13. The -6 volts, in turn, pinches off FET
5 in figure 2-2. Contact 9 and wiper 2 of S7-F connect -8
Q2. When the reference signal goes negative, the drop across
volts dc from XA2-16 through the same routing as
the emitter-to-base junction of PNP transistor Q4 causes the
described in d above to the multimeter.
base to go to -0.7 volt and the transistor conducts, causing
Q4-C to go to ground. When Q4-C goes to ground, it causes
g. Mentally perform step 6 of table 3-3 and refer to step
FET Q2 to conduct, which, in turn, grounds the signal on
6 in figure 2-2. Wiper 1 of S4-A connects +28 volts dc to
the noninverting input at AR2-3. Thus, the chopper circuit
grounds the noninverting input to AR2 each time the
contact 9 of S4-A, from which the voltage is connected to
reference signal at XA2-34 goes negative.
pin 28 of connector XA2. The voltage passes through CR16

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