Self-Test Theory.

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

2-4