B&K 1076, Инструкция по эксплуатации, Страница: 20 / 64

We will now shift our sync signal to the plate of the 6AU6 sync separator
and again observe the picture on the face of the CRT. We now find that the
intermittent sync condition occurs. This tells us that the trouble lies between
the plate circuit of the 6AU6 sync separator and the grid circuit of the 6BF6
sync amplifier. A few voltage and resistance measurements would now cer­
tainly point out the trouble. It might even be worth while to replace all of
the components that lie between plate of the 6AU6 and the grid of the 6BF6,
since this would save a great deal of time and would eliminate the necessity
of determining which component is intermittent.
FROM
VIDEO
SYSTEM
SYNC. AMP.
6
CB6
+130V
265V
SYNC. SEP.
6AU6
uu
20V.P-P
.01
\
s-i;Nc. AMP.,,,,,-llfl
SOV.P-P
2
6BF6
{4.7K
I IO VERT •
. 047
�YSTEM
4.7K
6.8
82
K
T
MMF +130
130V
265V
TO HORIZ.
SYSTEM
Figure 6---A sync separator system
As you can see, this sync injection method for locating intermittents will
in every case isolate the trouble to a particular stage. From that point on
the repair is very simple.
HOW TO USE THE TELEVISION ANALYST FOR TROUBLE
SHOOTING LOSS OF AUDIO
This trouble shooting procedure for Audio I.F. Stages applies to inter­
carrier type of sets.
Let us assume there is no audio in a TV receiver. Within a couple of
minutes we will find the defective stage by using the Television Analyst. Refer
to Fig. 7. Assume a shorted screen bypass capacitor (5000 mmf) on the 4.5 me
Audio I.F. amplifier.
To check the speaker and audio output stage, inject the 400 cycle audio
tone on the grid of the audio output tube (point A). A good tone will be heard.
Then move the signal injection point to the grid of the audio amplifier
(point B). Now use the 4.5 me audio I.F. output with 400 cycle tone modulation
and inject the signal at the plate of the sound I.F. amplifier (point C). You
will still hear the tone signal indicating all the stages from this point to the
loudspeaker are 0.K. Now the 4.5 me signal is injected on the grid of the
4.5 I.F. amplifier (point D), and the tone signal is no longer heard in the
loudspeaker. This immediately tells you that the trouble is in this stage.
A simple voltmeter test will discover the bad component, as no B+ or very
low B+ will appear on the screen of this tube. It is always a good practice
to check the screen dropping resistor under these conditions, to see if the
excessive current has caused it to increase in value.
18
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