Harris Gates One 994 9202 002, Техническое руководство

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U10, U7 and U8 are suspect. These are the
integrator amplifiers which take a square
wave inputs, and convert them to triangle
waves.
If the square waves are not getting to
integrator amplifiers U7 and U8, use the
oscilloscope to check the output of the 240
kHz oscillator at U11-3. This should be a
240 kHz square wave close to 5 volts peak-
to-peak.
If no such signal is present, U4 is possibly
at fault. If U11 is working properly, use the
scope to check the outputs of U4 at pins 2
and 12.
60 kHz square waves (5 V peak to peak)
should be at pins 2 and 12.
F.3.2.
Symptom: Imbalance In Output
Pulse Widths
Possible causes:
F.3.2.1.
Audio Imbalance
An imbalance in the two phases of the
DC/AUDIO circuitry is characterized by an
imbalance in the duty cycle between the two
outputs of both threshold comparators U9
and U10. Each dual comparator is driven by
one triangle wave and both phases of audio.
Any duty cycle imbalance between the two
outputs of either U9 or U10 is most likely
caused by a failure of U1 or U2 in the
DC/AUDIO circuitry.
Measure the voltages at DIP resistor R17
pin 7 and U1-14. These should be 2 volts or
less, equal, and opposite in polarity. R17 pin
7 will normally be positive and U1-14 will
be the negative mirror image. Major dis-
similarities in the voltage at U1-14 and R17
pin 7 are probably caused by a failure of U1.
F.3.2.2.
Triangle Wave Imbalance
An imbalance in the triangle waves driving
the output comparators will result in the out-
puts of U9 differing from those of U10. If the
DC/AUDIO balance is correct, both outputs
of U9 will be the same, but will differ in pulse
width from the outputs of U10.
Using an oscilloscope, check the triangle
waves at U9-5 and U10-5 per Figure F-3.
These signals should be exactly the same
(except for their phase relationship). Each
should be a 3.5-4.0 volt peak to peak 60 kHz
triangle wave.
Differences in peak to peak amplitude
may be caused by the square wave to trian-
gle wave integrator, U7 or U8.
F.3.3.
Symptom: Output(s) At J2 Al-
ways In A High State, Causing
One or More Pdm Amplifiers to
Conduct Full Time
This problem may be found without turn-
ing on the high voltage. Identify which out-
1 +20V Fuse, A15F1 .5 Amp fuse (3AG) used to p20
volt supply from over current condition.
2 -20V Fuse, A15F2 .5 Amp fuse (3AG) used to protect -20
volt supply from over current condition.
3 Zero Power Adjust A15R111
4 Flat/Bessel Select Control, A15S1 Selects type of frequency response
t r a n s m i t t e r w i l l h ave . H i g h e s t
modulation density will be obtained in
B E S S E L p o s i t i o n , w h i l e f l a t t e r
frequency response will be obtained in
FLAT position.
5 Audio Input Level Adjustment, A15R21 Adjusts audio input level from -10 to
+10 dBm.
Table F-1. PDM Generator, Controls and Indicators
1
2
3
4
5
Figure F-1. PDM Generator, Controls and Indicators
F-2 888-2314-001 Rev.AE: 03-05-2002
WARNING: Disconnect primary power prior to servicing.