32. NO LOUD RUSHING NOISE HEARD AT THE COMMANDER'S BOX (EPC STEP 30).
a. Situation 18.
This indicates the A-RT muted monitoring (monitor
switch at ALL) circuit is bad. This symptom is caused by an open or short
circuit. Trace the A-RT muted monitoring circuit and identify the following
possible bad items of equipment: AM-1780, CX-4723 (between AM-1780 J501 and
J-3513 J7), J-3513, MT-1029, and A-RT (Figure 99. Issued as adjunctive
b. General test procedures.
You must determine the type of test and
the location of the test points to identify the actual bad item of
equipment. Troubleshooting techniques for this type of defect are circuit
Circuit disturbance is a test made on an audio (transmit or receive)
circuit, where the handset elements can be listened to. This test
is accomplished by using your multimeter (setup for resistance, 2K
Place one of the test leads on one side of the circuit.
Listen to the handset element (mike or phone) while tapping the
other side of the circuit with the other test lead. If the circuit
is good, a clicking sound will be heard in the element.
c. Test procedure 72. The first test is at the AM-1780 J511 pin K to
pin A (use your system diagram).
Circuit disturb the monitor circuit, while listening to the
handset (connected to commander's C-2298 J802) (monitor switch at
If circuit disturbance is heard, the AM-1780 is good, check for
an open or short within the system.
If circuit disturbance is not heard, check for an open or short
within the system.
Turn the RT and AM-1780 to OFF.
Remove the CX-4723 from the AM-1780 J501.
Remove the RT from the MT-1029.
Measure continuity on the MT-1029 J24 pin A to pin K for a short.
If zero ohms
If infinity is measured, the circuit is not shorted.
Then measure J24 pin K to the CX-4723 pin K for a open.
If infinity is measured, the circuit is open.
If zero is measured, the circuit is not open.