terminal. The green and black wires are connected to pins A of J101. The
red and white wires connect to pins B of J101. Pin A is grounded in the AM-
7152 and Pin D is tied to ground through A muting capacitor. This provides
muting ground between the A and B radios when connected in parallel. J101
is connected in parallel with J103 to provide battery power and muting line
between A and B radios. J103 connects to the parallel radio over cable CX-
4721. A voltage measurement at pin A to pin B at J103 can be used to ensure
that voltage is present at J101 of the AM-7152. Regulated power from the
AM-7152 J104 is applied to P1 of AM-6874 over cable PN 1623814. Ground can
be found at pins A, B, and C of J104, and regulated power can be found at
pins F, H, and J of J104. If power is present at J1 of the cable, any power
problem must be in the AM-6874 or the RT 1209. To determine which of these
components is causing a power problem, you must substitute known good
components for the suspected components. You can measure voltage at pins 38
and 39 to ground at AM-6874 interface connector. If 24 volts is present at
these pins, suspect the RT-1209; and if this voltage is absent, suspect the
AM-6874. This test is not conclusive, it only tells you which component to
suspect of being bad for your initial substitution.
b. Transmit and receive radio frequency (RF) involves two RF cables.
Cable PN 1623848 is connected to J1 of AM-6874, and the other end connects
to J201 of antenna switch unit SA-2365. Depending on the switch setting on
the SA-2365, RF is carried from the center pin from J201 to the center pin
of J202 in the top switch position, or middle position (through a 50 PF
capacitor), or to J203 in the bottom switch position.
The shells ground
shields of all three connectors in the SA-2365. J202 feeds the whip antenna
through cable PN 1623849-4 to the antenna base. The SA-2365 should always
be used in this position when using balanced 50-ohm antennas and used in the
top or middle position when using the vehicle whip. The only parts in the
SA-2365 that can cause RF problems are the switch and the 50 PF capacitor in
the 10-MHz to 30-MHz range for the whip antenna.
Resistance measurements
can be used to check out the RF cables and SA-2365. (See Figure 25.)
c. The audio cable from J2 of the AM-7152 to the RT-1209 J2 is a five-
wire cable. Pin A of the audio jacks is grounded microphone shield. Pin B
is receive audio and sidetone. Pin C furnishes ground to key the RT through
the PTT switch.
Pin D carries transmit audio.
Amplified audio for the
loudspeaker is carried over pin E. Pin F is used only for a key line from
communications security (COMSEC) equipment. This cable can be checked with
resistance measurements. The RT keying can be checked by grounding pin C.
Pin B can be checked for 1 to 3 volts AC while receiving a signal.
d. J102 is connected to the AN/VIC-1, when it is used, by cable CX-
4723.
This is checked by the same methods you use for other radios used
with the AN/VIC-1.
e. You already know how to check out the audio accessories which are
the same as those used with AN/VRC-12 series radios.
f. If you suspect the RT-1209 or AM-6874 is the cause of a problem,
this can be confirmed by configuration as AN/PRC-104 and performing an EPC.
However, you can prove that the RT-1209 and AM-6874 are good by the same
method.
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