S I N G L E - C H A N N E L A P P L I C A T I O N S
introduction.
In addition to the dual-trace applications previously
outlined, there are, of course, many servicing and
laboratory applications where only single-trace or
single-channel operation of the oscilloscope is re-
quired. By setting the MODE switch to CH2 and
using the C H 2 amplifier, many flexible operations
will be achieved; and, in addition, by placing the
M O D E switch to A D D and the C H 2 polarity switch
to the P U L L I N V E R T position. Whatever waveform
is obtained can be inverted in polarity if desired by
the operator.
T e l e v i s i o n S e r v i c i n g :
A triggered sweep oscilloscope is advantageous in
servicing and aligning television receivers. This
oscilloscope also includes several features that
were incorporated to make television servicing and
V I D E O signal observation easier and more
comprehensive.
These feature inc ude:
* With the S Y N C switch set to V I D E O position,
the S W E E P T I M E / D I V control automatically
selects the V I D E O - F R A M E sync at sweep
speeds appropriate for viewing frame and
V I D E O - L I N E sync at sweep speeds appropriate
for viewing lines.
* Wide bandwidth for high resolution video and
high speed pulse presentation.
S i n g l e - t r a c e Operation and P e a k - t o - P e a k
Voltage R e a d i n g s :
For general troubleshooting and isolation of
troubles in almost any electronic equipment, the
oscilloscope is an indispensable instrument. It
provides a visual display of the absence or presence
of normal signals. This method (signal-tracing)
may be used to trace a signal by measuring several
points in the signal path. A s measurements
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 shown much more than
the mere presence or absence of signals. It
provides a peak-to-peak voltage measurement.
The schematic diagram or accompanying service
data on the equipment being serviced usually
includes waveform pictures. There waveform
picture include the required sweep time and the
normal peak-to-peak voltage. Compare the
peak-to-peak voltage readings on the oscilloscope
with those shown on the waveform pictures. Any
abnormal readings should be followed by additional
readings in the suspected circuits until the trouble
is isolated to as small an area as possible.
Composite Video W a v e f o r m A n a l y s i s
Probably the most important w a v e f o r m in
television servicing is the composite waveform
consisting of the video signal, the blanking pedestal
signal and the sync pulses.
Fig. 19
and
Fig. 2 0
show typical oscilloscope traces when observing
composite video signals synchronized with ho-
rizontal sync pulses and vertical blanking pulses.
Composite video signals can be observed at various
stages of the television receiver to determine
w h e t h e r c i r c u i t s are p e r f o r m i n g n o r m a l l y .
Knowledge of waveform makeup, the appearance
of a normal waveform, and the cause of various ab-
normal 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, noting
the waveform at various points in the video
amplifier. To set up the oscilloscope for viewing
composite video waveforms, use the following
procedures:
1. Turn the television set to a local channel. A
test tape or a signal generator also can be used
for service work.
2. Set the M O D E switch to C H 2 position.
3. Set the S W E E P T I M E / D I V switch to the 10
us
position for observing T V horizontal lines or to
the 2 ms position for observing TV vertical
frames.
4. Set the S Y N C switch to V I D E O + o r V I D E O -
position.
5. Set the S O U R C E switch to INT position.
6. Best overall sync performance is obtained
when the T R I G L E V E L / P U L L A U T O control is
pushed in. It may be pulled out initially to
provide continuous sweep during set-up.
7. Set the C H 2 A C - G N D - D C switch to the A C
position.
8. Connect the ground clip of the probe to the
c h a s s i s . With the probe set for 10 : 1
attenuation, connect the tip of the probe to the
video detector output.
9. Set the C H 2 V O L T S / D I V switch for the largest
vertical deflection possible without going
offscale.
10. If necessary, rotate the T R I G L E V E L control to
a position that provides a synchronized display.
1 1 . Adjust the sweep time V A R I A B L E for two ho-
rizontal lines or t w o vertical f r a m e s of
20
