28. R-442 AUDIO OUTPUT CIRCUIT.
a. Situation 14.
When performing EPC step 24, NO rushing noise is
heard in the earphone and speaker or rushing noise is heard at only one but
not the other. This indicates the R-442 AUDIO output circuit is bad. This
symptom is caused by an open or a short circuit. Trace the circuit on your
system diagram and identify the following possible bad items: R-442, MT-
1898, J-3514/U, CX-7058, and AM-1780.
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 61.
The first test is at the MT-1898 J-14.
Remove the R-442 from the MT-1898.
Measure continuity at J14 pin E to pin L. This measures the X-
MODE IN, X-MODE OUT (series) circuit of the MT-1898 and J-3514/U.
If infinity is measured, the circuit is open and the MT-1898 or
the J-3514/U is bad. To check the MT-1898.
d. Test procedure 62.
Disassemble the MT-1898 and remove P1 of J-
3514/U from J12.
Measure continuity at J14 pin E to J12 pin E and J14 pin L to J12
pin D.
If either measurement is infinity, the MT-1898 is bad (open).
If zero ohms is measured on both circuits, the MT-1898 is good
and the J-3514/U is bad.
e. Test procedure 63. When measuring continuity at J14 pin E to pin L,
zero ohms is measured. The X-MODE IN, X-MODE OUT circuit is not open (Test
procedure 63).
Measure at J14 pin E or pin L to pin A for a short.
If zero is measured, MT-1898 or J-3514/U is shorted.
To test the MT-1898 for a short, disassemble the MT-1898 and
remove P1 from J12.
Remeasure at J14 pin E and pin L to pin A.
If zero ohms is measured, the MT-1898 is bad.
If infinity is measured, the J-3514/U is bad.
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