Trio CS-1560AII Instruction Manual Download Page 18

Page: 18 / 31

as being either Field 1 or Field 2 VITS information, the
probe corresponding to the waveform display can be
used for signal-tracing and troubleshooting, and the
remaining probe should be left at the video detector

test point to ensure that the sync signal is not in-
terrupted. If the sync signal is interrupted, the
waveform displays may be reversed because, as
previously explained, there is no provision in the os-
cilloscope to identify either of the two vertical fields

which comprise a complete frame.

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 out-

lined, there are, of course, many servicing and laboratory

applications where only single-trace or single-channel
operation of the oscilloscope is required. By setting the

MODE switch to CH2 and using the CH2 amplifier, many

flexible operations will be achieved; and, in addition, by plac-

ing the MODE switch to S U B position (with the CH 1 DC-
GND-AC switch in the GND position), whatever waveform is

obtained can be inverted in polarity if desired by the
operator.

Television Servicing:

A triggered sweep oscilloscope is advantageous in ser-

vicing and aligning television receivers. This oscilloscope
also includes several features that were incorporated to

make television servicing easier observation and more com-
prehensive.

* With the SYNC switch set to TV position, the S W E E P

TIME/DIV control automatically selects the TV vertical

sync at sweep speeds appropriate for viewing frames and

TV horizontal sync at sweep speeds appropriate for view-

ing lines.

* Wide bandwidth for high resolution video and high speed

pulse presentation.

Single-trace Operation and Peak-to-Peak

Voltage Readings:

For general troubleshooting and isolation of troubles in

television receivers, the oscilloscope is an indispensable in-
strument. 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 shows much more than the

mere presence or absence of signals . It provides a peak-to-
peak voltage measurement of the signal as well as presenta-
tion of waveforms. The schematic diagram or accom-
panying service data on the equipment being serviced usual-
ly includes waveform diagram. This waveform diagram

includes 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 diagram.

Composite Video Waveform Analysis:

Probably the most important waveform in television ser-

vicing is the composite waveform consisting of the video
signal, the blanking pedestal signal and the sync pulses. Fig.

17 and Fig. 18 show typical oscilloscope traces when

observing composite video signals synchronized with
horizontal sync pulses and vertical blanking pulses. Com-
posite video signals can be observed at various stages of the
television receiver to determine whether circuits are perfor-

ming normally. Knowledge of waveform makeup, the
apperance of a normal waveform, and the causes 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, noting the waveform at various points
in the video amplifier.

T E L E V I S I O N S E T

Fig. 16.

Set-up for viewing

horizontal

fields of composite video signal

H O R I Z O N T A L

S Y N C P U L S E

HORIZONTAL

BLANKING

PULSE

I F

A M P