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A.
High Distortion
B.
Imporper
Frequency Response
C.
Will not Modulate at all
D.
High FM Noise
E.
High AM Noise
When it is known that any of th o above listed faults exist,
it
will save time to first isolate the trouble to either the audio
sta3es or the rest of the exciter unit.
It is easy to
-
check the
output of the audio stages by connecting a ground lead from a
black test point and a " hot" lead from TP120.
These two loads
can then be run to the input of a distortion analyzer.
If these
leads are very long,
they should be shielded or they may pick up
external hum and noise.
HIGH DISTORTION
When high distortion is present,
it can usually be divided into
three categories.
o
o
1.
Distortion high throughout the audio spectrum 30 to
15,000 cycles.
2.
Distortion high at low frequencies only.
3.
Distortion high at high frequencies only.
When distortion is high through the audio spectrum of 30 to
15,000 cycles the fault is apt to lie in the audio stages of
V116 and V117.
It is wise to check these stages anyway when
modulation difficulties are experienced.
A failure of any
component in the audio stages could cause the distortion te
rise.
Checking volta , es against the schematic should show the
difficulty.
Changing u tube will usually cure the trouble.
It is characteristic of an FM system that the greatest diffi-
culty in attempting to modulate occurs at the low frequencies.
When
-
the overall distortion is high between 30 and 400 cycles
only, the trouble will usually be found in either one or both
of the modulator stages or in the pulse circuitry just
preced-
ing them.
A check of the waveform in stages V101 thru V106 is
advisable.
These can be checked against drawing 826
7991 001.
-23—
M6095 Exciter
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