put(s) of the PDM generator are at fault by
connecting a voltmeter or oscilloscope to
R45, R46, R62, and R63. The faulty out-
put(s) will be as much as 14 volts positive
if read on a voltmeter, or continuously high
if observed on a scope (DC coupled). Refer
to Figue F-4.
F.3.4. Symptom: Only One Output High
This is probably a fault of U9 or U10
depending on the output line in question.
F.3.5. Symptom: Two Outputs Are High
If the signals at R45 and R62 are both
high, U1 most likely has failed. Check the
voltage at U1-14. Normally it is -2 volts or
less, but in this case it might be +2 volts or
greater.
F.3.6. Symptom: All Four Outputs Are
High
CheckthePDMLevelreadingontheMul-
timeter. If it is excessively high (such as
pinned) the problem would be on the Con-
troller in the power level summing circuitry
U19.
If the PDM Level is okay, the problem
couldbecausedbyU1,U2,U12orU15on
the PDM Generator. Check the voltage at
R17 pin 7. Normally it is +1 to +2 volts, but
in this case may be further negative.
Check the output of the audio input am-
plifier at U1 pin 8. This should be practi-
cally zerovolts.If itis not,tryreplacing U1.
If no fault is found with U1, try replacing
U12.
U15 may be the cause of the problem ifno
other is identified.
Figure F-2
Upper Trace - U4-2, 5Vp-p
Lower Trace - U4-12, 5Vp-p
Figure F-3
Upper Trace - U9-5, 3.5-4Vp-p
Lower Trace - U10-5, 3.5-4Vp-p
Figure F-4
Upper Trace - R63, right side, 13Vp-p
Lower Trace - R62, right side, 13Vp-p
Rev.AE: 03-05-2002 888-2314-001 F-3
WARNING: Disconnect primary power prior to servicing.
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