TM 11-6625-821-45
positive feedback to the base of Q1. The two oppo-
dc is also applied to the inverter, which converts
site phases of the 400 cps signals are amplified by
the 27.5 volts dc to 26 volts, 400 cps. (Refer to c
push-pull amplifier Q2 and Q3 and is applied to
below for a detailed description of the inverter.)
The 26 volts, 400 cps from the inverter is connected
to switch S302B in the control unit through fuse
negative-going signal. During the next half cycle,
F2. When switch S302B is set to any position other
signal polarities are exchanged. The secondary of
than OFF, the 26 volts, 400 cps is applied directly
T1 steps up the ac signal to 26 volts. The ac voltage
to the test set BEARING INDICATOR and to the
output is adjusted by variable resistor R1, which
receiver through switch S4D. The BEARING
supplies base voltage to Q1.
INDICATOR and the receiver use this voltage for
d. Control Unit. Detailed functioning of the con-
reference and excitation of the synchros and re-
trol unit is contained in section III of this chapter.
solvers. When the RECEIVER-CONTROL switch
Section III describes interunit circuit functioning.
is set to CONTROL, switch S4B places a load
Figure 5-5 is
the schematic diagram for the control
across the inverter output. The load, comprised
unit.
of inductor L11, resistor R10, and potentiometer
e. Cab/es. Four cables are supplied with the test
R11, is used in the absence of the receiver that
set. A schematic diagram of the cables is shown in
normally applies the load. Potentiometer R11 ad-
justs the size of the load to obtain the correct
11569/ARM-93 (cable W1) connects the external
output voltage from the inverter. The 26 volts, 400
27.5-volt dc power source to the test set. Cable
cps is also applied to the base of ac indicator con-
trol Q1 through current-limiting resistor R6.
When the positive cycle of the 26 volts, 400 cps
(cable W2) is a coaxial cable used to connect rf sig-
nals to the test set. Cable Assembly, Special Pur-
occurs, transistor Q1 conducts and applies ground
pose, Electrical CX-11570/ARM-93 (cable W3) con-
to AC indicator DS2. The ground completes a dc
nects the LOOP ANTENNA output of the test set
path and lights the AC indicator. If the 26 volts,
to the loop -antenna input of the receiver. Cable
400 cps is turned off, transistor Q1 will cut off and
Assembly, Special Purpose, Electrical CX-11571/
the AC indicator will no longer light.
ARM-93 (cable W4) extends the inverter away
from the test set when repairing the inverter.
ARM-93 provides interconnection between the
control unit and the receiver when RECEIVER-
1-5. Detailed Functioning of
Control
CONTROL switch S4 is in the RECEIVER posi-
Section
tion. Detailed functioning of the interconnect cir-
a. General. RECEIVER-CONTROL switch S4,
cuitry is included in the interunit circuit function-
in the CONTROL position, selects the portion of
ing in section 111 of this chapter.
the test set that is used to test the control unit.
CONTROL TEST switch S3 selects various con-
volts dc to 26 volts, 400 cps ac. The inverter in-
trol unit circuits and connects them to the CON-
cludes 400-cps oscillator Q1 coupled to a push-pull
amplifier consisting of Q2 and Q3. Transistor Q1
TROL TEST terminals. An ohmmeter is con-
nected to the CONTROL TEST terminals to mea-
oscillates with positive collector-to-base feedback
sure the resistance of the selected circuits in the
introduced by the parallel resonant tank circuit
control unit. Subparagraphs b through f below
comprising capacitor C2 and center-tapped induc-
tor L1. At the resonant frequency of 400 cps, the
describe detailed functioning of the control por-
tank circuit presents an impedance that applies a
tion of the test set. Included in these subpara-
signal to the base of Q1 that is 180 out of phase
graphs are simplified schematic diagrams which
with the collector output signal. A signal passing
will help in understanding the following descrip
from the base to the collector is shifted 180 and,
tions and will also help in troubleshooting the
adding the tank circuit 180 phase shift. results in
control unit.
Change
2