B&K 1076, Инструкция по эксплуатации

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are lost when the intermittent trouble appears, it is obvious that the trouble
must be in the R.F. tuner, I.F. amplifier, Video detector, Video amplifier or
A.G.C. circuits.
The Television Analyst will now be used to locate the source of the trouble.
The signals available from the instrument will be injected into the receiver
at various points, so that by the process of elimination the trouble can be
analyzed down to one stage.
First it is necessary to disable the A.G.C. circuits by connecting a bias
supply to the A.G.C. buss which feeds A.G.C. voltage to the tuner and I.F.
amplifier stages. (Incidentally, if the trouble were in the A.G.C. circuit,
using this external bias supply would probably eliminate any symptoms of
trouble. This would indicate that the source of trouble was in the A.G.C.
Circuits).
Now by feeding R.F. signal into the antenna terminals of the set (A) the
test pattern and sound will intermittently disappear, just as it did on the
local TV stations.
By moving our signal injection point stage by stage from the antenna ter­
minals to the picture tube, we can localize the trouble. Still using R.F. ouput,
inject the signal on the grid of the R.F. converter tube (B). If the intermit­
tent still appears, it means that the trouble is NOT in the R.F. amplifier stage,
or the R.F. oscillator.
Now we switch the instrument output to the I.F. signal, and inject this signal
at the same point at the grid of the converter (B). (Note:-If the intermit­
tent appeared when R.F. signal was fed to the grid of the converter, and it
did not appear when I.F. signal was fed into the grid of the converter, then
the trouble would have been pin-pointed directly to the R.F. oscillator).
With I.F. signal fed into the converter grid (B) we find that the intermit­
tent still appears. That means the R.F. oscillator is not causing the trouble.
Now we move our signal cable to the grid of the first I.F. amplifier (C).
Finding the trouble still intermittently appearing, we move our signal to the
second (D) and the third (E) I.F. stage. (Obviously, if the trouble appeared
when injecting on the grid of the second I.F. stage (D), but no longer showed
up when injecting signal to the third I.F. stage (E), the trouble would have '
been pin-pointed to the second I.F. stage).
Sine� the intermittent still appeared, . the Television Analyst signal output
is now switched to Video and the signal is injected into the video detector
load. (See Figure 5). This is usually around a 4,000 ohm resistor and can
easily be located because it will have a video peaking coil associated with it.
(Note:-For video signal make sure you are using the correct output cable
as it is not taken from the same output jack as the R.F.-1.F. signals. Also, if
the picture appears negative, reverse the polarity of the video signal with the
Video Polarity (+or-) Switch).
Since the intermittent trouble still appears, the video detector has been
eliminated from suspicion and the video signal is injected on the grid of the
first video amplifier (F). The intermittent trouble still shows up at this point.
The video signal is now injected into the grid of the second video amplifier
tube (H) after reversing the polarity with Video Polarity (+ or -) Switch
to compensate for the 180
°
phase reversal in the first amplifier tube. Now,
for the first time, the intermittent disappearance of sound and video is no
longer evident. The trouble has been isolated to an area between the grid
of the first video amplifier (F) and the grid of the second video amplifier (H).
Now to use the Television Analyst once more to check the coupling capacitor
(C-4) from the plate of the first video amplifier to the grid of the second
video amplifier. Inject the video. signal on the plate side (G) of the coupling
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