B&K 1076, Instruction Manual

Page: 35 / 64

could be developed by the circuit and it would prevent the develop­
ment of the normal amount of high voltage or the normal amount of
horizontal drive for the yoke. If C-2 should open, the circuit would
again be disrupted by the lack of boost B+ voltage. B+ voltage,
however, would still appear because the damper tube and L-1 would
still be intact.
The foregoing examples indicate the complete flexibility of this
instrument. With continuous use the technician will certainly develop
his own procedure which will completely remove all of the com­
plexities of Sweep Circuit Analyzing.
TROUBLE SHOOTING CHROMA CIRCUITS
Loss of color, weak color or distorted color can occur in the R.F. or I.F.
sections of a receiver as well as in the Chroma Circuits. The Analyst is par­
ticularly useful in trouble shooting this type of complaint as either the R.F.
or I.F. signal may be modulated with the Rainbow Color signal and this
signal injected, into the R.F. or I.F. stage by stage to localize the defective
stage.
The Chroma signal is also available at the output jack labeled Color and
may be injected directly into the Video Detector, Video Amplifier, Band pass
Amplifier or to the grid of low level demodulators.
These tests quickly pin down complaints of no color, weak color, and dis­
torted color. They also localize phase errors by showing the wrong sequence
of colors.
Phase errors arise in the Chroma section, or in the I.F. section. It is pos­
sible for the R.F. section or Video section to ·cause phase errors, but these
are less common trouble points. If you inject the Chroma signal into the
Band pass Amplifier and get a normal color pattern the next step is to inject
an I.F. signal modulated with chroma information at the input of the I.F.
Amplifier.
When a phase error is found in the latter test, it is indicated that the I.F.
Amplifier is in need of proper alignment. On the other hand, a phase error
in the former test indicates the need of Chroma circuit alignment.
A color bar pattern slide is enclosed in the accessory package of your Tele­
vision Analys_t to enable you to convert the rainbow pattern which it produces
into a color bar pattern of known colors. Too high a setting of the Receiver
Chroma Control will result in having only the three primary colors displayed.
At this point it might be well to review the principle of operation of a rainbow
pattern and then relate it to a color bar pattern.
The different hues that can be produced in a color TV receiver are obtained
by shifting the phase of the color sub-carrier of the transmitted signal with
respect to the reference burst which occurs during the horizontal blanking
interval. For example, if the phase of the sub-carrier is shifted slowly through
a complete 360
°
with reference to the burst signal, the hue will change from
yellow to orange, to red then magenta, blue cyan and green, and all of the
intermediate hues between those colors. If the phase of the sub-carrier signal
is continuously changed thru a full 360
°
during the interval of one horizontal
line and repeats itself for each following horizontal line, a continuous rain­
bow of colors will be produced. Instead of shifting the phase of the sub-carrier
in the TV Analyst, we will make the frequency of the sub-carrier lower than
the color oscillator in the TV receiver by 15,750 cycles. There will then be a
one cycle per line difference between the sub-carrier and the oscillator in the
receiver. Since over a period of one horizontal line there is one cycle differ­
ence between the two signals, we have effectively created a 360
°
phase shift
per horizontal line which will repeat itself each horizontal line. This will
result in a rainbow display showing each of the colors in the color spectrum
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