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normal signals. This method (signal-tracing) may
be used to trace a signal by measuring several
points
in the
signal path.
proceed along the signal path, a point may be
found where the signal disappears. When this
happens, the source of trouble has been located.
However, the oscilloscope shows much more than
the mere presence or absence of signal. It provides
a
peak-to-peak
voltage
schematic diagram or accompanying service data
on the equipment being servied usually includes
waveform pictures. There waveform pictures in-
clude the required sweep time and the normal
peak-to-peak voltage.
Compare the peak-to-peak
voltage
readings
and
cilloscope with those shown on the waveform pic-
tures. Any abnormal readings should be followed
by additional readings in the suspected circuits un-
til the trouble is isolated to a s small an area a s
possible.
B U R S T
\
H O R I Z O N T A L
S Y N C P U L S E
T E L E V I S I O N S E T
Fig. 19 S e t - u p for v i e w i n g horizontal fields of composite video signal
V I D E O
V E R T I C A L
S Y N C
P U L S E
Fig. 2 0 Set-up for viewing vertical fields of composite video signal
A s
measurements
measurement.
T h e
waveshape on
the
os-
V I D E O
H O R I Z O N T A L
B L A N K M N G
P U L S E
I F
A M P
V I D E O
D E T E C T O R
V E R T I C A L
B L A N K I N G
V I D E O
I F
A M P
D E T E C T O R
T E L E V I S I O N S E T
Composite Video Waveform Analysis
Probably the most important waveform in televi-
sion and video servicing is the composite waveform
consisting of the video signal, the blanking pedestal
signals and the sync pulses. F i g . 19 and Fig. 2 0
show typical oscilloscope traces when observing
composite video signals synchronized with horizon-
tal sync pulses and vertical sync pulses. Composite
video signals can be observed at various stages of
the television receiver to determine whether cir-
cuits are performing normally.
waveform makeup, the appearance of a normal
waveform, and the cause of various abnormal
waveforms help the technician locate and correct
many problems. The technician should study such
waveforms in a television receiver known to be in
good operating condition, nothing the waveform at
varous points in the video amplifier. To set up the
o s c i l l o s c o p e
for
waveforms, use the following procedures:
•=
V I D E O
A M P
S O U N D
I F
C O L O R
V I D E O
A M P
S O U N D
I F
C O L O R
Knowledge
v i e w i n g
c o m p o s i t e
P I C T U R E ]
V I D E O
T U B E ;
A M P
I F
P I C T U R E i
V I D E O
T U B E J
A M P
I F
of
v i d e o
19
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