V I D E O
V I D E O
D E T E C T O R
T E L E V I S I O N S E T
V I D E O
A M P
S O U N D
I F
P I C T U R E
T U B E
C O L O R
I F
Fig. 17. Set-up for viewing
vertical
fields of composite video signal
13. Push in the TRIGGERING LEVEL control and rotate to
a position that provides a well synchronized display.
14. Adjust the INTENSITY and FOCUS controls for the
desired brightness and best focus.
15. To view a specific portion of the waveform, such as
the color burst, pull the ^ •POSITION control for X 5
magnification. Rotate the same control left or right to
select the desired portion of the waveform to be view-
ed.
16. The polarity of the observed waveform may be revers-
ed when moving from one monitoring point to
another; therefore, it may be necessary to reverse the
polarity of the SYNC switch.
Sync Pulse Analysis:
The IF response of a television receiver can be
evaluated to some extent by careful observation of the
horizontal sync pulse waveform. The appearance Of the
sync pulse waveform is affected by the IF amplifier bandpass
characteristics. Some typical waveform symptoms and their
relation to IF amplifier response are indicated in Fig. 18.
Sync pulse waveform distortions produced by positive or
negative limiting in IF overload conditions are shown in Fig.
19.
18
V E R T I C A L
S Y N C
P U L S E
V E R T I C A L
B L A N K I N G
I F
A M P
V I D E O
A M P
To set up the oscilloscope for viewing composite video
waveforms, use the following procedures:
1. Tune the television set to a local channel.
2. Set the MODE switch to CH2 position.
3. Set the S W E E P TIME/DIV switch to the 10/us position
for observing TV horizontal lines or to the 2ms position
for observing TV vertical frames.
4. Set the SYNC switch to the T V + position.
5. Set the SOURCE switch to the CH2 position.
6. Set the TRIGGERING LEVEL control to the AUTO
position.
7. Set the CH2 AC-GND-DC switch to the A C position.
8. Connect a probe cable to the CH2 INPUT jack.
Connect the ground clip of the probe to the television
set chassis.
With the probe set to 10 : 1 attenuation, connect the
tip of the probe to the video detector output of the
television set.
9. Set the CH2 VOLTS/DIV switch for the largest vertical
deflection possible without going off-scale.
10. Rotate the TRIGGERING LEVEL control to a position
that provides a synchronized display.
11. Adjust the sweep time V A R I A B L E for two horizontal
lines or two vertical frames of composite video display.
12. If the sync and blanking pulses of the displayed video
signals are positive, set the SYNC switch to the TV-f-
position; if the sync and blanking pulses are negative,
use the T V — position.
