34. NO SIDETONE (EPC STEP 31).
a. Situation 20.
This indicates the A-RT modulation circuit is bad.
This symptom is caused by an open circuit.
Trace the A-RT modulation
circuit and identify the following possible bad items of equipment: AM-1780,
CX-4723 (between AM-1780 and J-3513/U), and J-3513/U (Figure 101. Issued as
adjunctive material.).
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 technique for this type of defect is continuity
measurement.
c. Test procedure 75.
The first test is at the AM-1780.
Turn the RT and AM-1780 to OFF.
Remove the two CX-4723s from J504 and J501.
Measure continuity on the AM-1780 J504 pin K to J501 pin U.
If infinity is measured, the AM-1780 is bad.
If zero ohms is measured, remove the RT from the MT-1029 mount.
Disassemble the MT-1029 mount.
Remove the CX-4723 from the J-3513/U J7.
Measure continuity on the CX-4723, end-to-end, pin U.
If infinity is measured, the CX-4723 is bad.
If zero ohms is measured, the J-3513/U is bad.
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