T.O. 33AF-3-358-11/TM 11-6625-842-15
Section IV
NAVAIR 16-30APM239-2
Paragraphs 4-1 to 4-10
SECTION IV
MAINTENANCE INSTRUCTIONS
4-1.
SCOPE.
4-2.
This section contains a functional description of the test set circuitry, checkout procedures. Calibration
check procedures, troubleshooting procedures, schematic diagrams, and other information pertinent to the
maintenance of the equipment.
FUNCTIONAL DESCRIPTION.
4-3.
4-4.
GENERAL. Transponder Set Test Set AN/APM-239A is a portable test set designed for the mainte-
nance support of the IFF transponder receiver-transmitters enumerated in paragraph 1-4.
4-5.
figure 4-1, illustrates the relationship of the various circuits in the test set, and figure 4-4 provides a sche-
matic diagram of the unit.
4-6.
A-C AND D-C CONTROLS. Incoming a-c power is applied through 6AMP POWER circuit breaker CB1
to AC CONTROL autotransformer T1. This control is adjusted to obtain 115 volts ac. The 115-volt a-c out-
put of the autotransformer is applied via 2 AMP AC fuse F1 to METER SELECT switch S21 in the a-c and d-c
voltmeter and ammeter circuits. The input ac power is also applied to DC CONTROL autotransformer T2
which adjusts the primary voltage of transformer T3 in the power supply circuit. When power is applied to the
AC and DC CONTROL autotransformers via circuit breaker CB1, the white POWER ON indicator is illuminated.
4-7.
POWER SUPPLY CIRCUIT. Transformer T3 develops an output voltage (approximately 35 volts rms
across terminals 3 and 4), depending on the autotransformer setting. This output is full-wave rectified by
diodes CR1 to CR4 and is then filtered by inductor L1 and capacitor C1. The resulting 28-volt d-c output is
then applied across bleeder resistors R1 and R2 to METER SELECT switch S21 in the a-c and d-c voltmeter
and ammeter circuits. Transformer T3 also develops 28 volts ac across terminals 7 and 5, and 6 volts ac
across terminals 6 and 5, which are applied to the PANEL LIGHTS switch. This switch selects either 6 or 28
volts ac as the panel light voltage which is then applied via connector PI to the transponder set control.
4-8.
A-C AND D-C VOLTMETER AND AMMETER CIRCUITS. . METER SELECT. switch S21 receives 115-
volts a-c at pin 2, and +28 volts dc at pins 5 and 12. When the switch is in the AC position, 115 volts a-c is
applied via pins 2 and 1 of the switch to ammeter M2. The 115 volts is also applied to half-wave rectifier CR9
which converts the a-c to d-c for use by the voltmeter. The resulting dc is applied, via pins 10 and 11 of the
switch, to voltmeter M1 which is calibrated to indicate the a-c voltage from the, half-wave rectified a-c. The
115 volts ac is applied to the receiver-transmitter under test via TRANSPONDER connector J2 (pin C15) and to
the computer via MODE 4 COMPUTER connector J4 (pin 1) through ammeter M2 which indicates the a-c cur-
rent being drawn. The 28 volts dc is applied, via pins 5 and 4 of METER SELECT switch S21 and 10 AMP DC
fuse F2, to output connectors J3, J4, and P1 and to POWER MODE switch S20. This switch inserts 1/2 AMP
DC fuse F3 into the 28-volt dc output line to TRANSPONDER connector J2 when in the AC/DC position, and re-
moves this fuse when in the DC ONLY position. It also opens 115 volt circuit to J2-C15 when in the DC ONLY position.
4-9.
When the METER SELECT switch is in the DC position, 115 volts a-c is applied via pins 2 and 3 of the
"
switch to the receiver-transmitter under test via TRANSPONDER connector J2 and to the computer via MODE
4 COMPUTER connector J4. The 28 volts dc is applied via pins 5 and 6 of the METER SELECT switch to am-
meter M2 and via pins 12 and 11 of the switch to voltmeter M1 which indicates the d-c current and voltage,
respectively. The 28 volts dc is applied via the ammeter, and 10 AMP DC fuse F2, to output connectors J3,
J4 and P1, and to POWER MODE switch S20. This switch operates in the same manner as described earlier,
and the 28 volts dc is applied to the receiver-transmitter under test via TRANSPONDER connector J2.
4-10. REFERENCE REGULATOR. A +28-volt d-c level is applied to the reference regulator dropping re-
sistor, R3. This resistor and filter capacitor C2 function in conjunction with zener diode VR1 and diodes CR5
and CR6 to provide the reference voltages required for the Mode C encoder simulator circuits. Zener diode
VR1 provides an 18.5-volt drop while diodes CR5 and CR6 provide 0.75-volt drops each. Therefore, at the
anode of CR5, a 1.5 volt d-c reference voltage is picked off and applied to the Mode C encoder simulator cir-
cuits. At the cathode of VR1, a 20-volt d-c reference voltage is picked off and applied to the Mode C encoder
simulator circuits.
Change 4 4-1
