and the test pattern signal tuned in. The displayed picture appears in Fig. 11.
We must now take the video output signal from the Analyst and inject this
signal to the grid of the 1st video amplifier. The result is viewed on the
television receiver's picture tube. We observe that the displayed picture is
satisfactory and we see the normal test pattern signal appears properly in
sync. We must therefore conclude that the trouble does not lie in the video
portion of the receiver. We now select an I.F. signal from the Television
Analyst of the proper frequency and inject this signal to the grid of the
1st Video I.F. amplifier. This is point A in Fig. 12. Examination of the picture
displayed on the receiver picture tube shows a negative picture that is out
of sync. This is the same result that we saw in Fig. 11. Therefore, the trouble
apparently lies in the I.F. portion of the receiver. We will now try to isolate
the trouble to a specific stage.
lsT.
VIDEO
1.F. AMP.
=
B+
-=
B+
TO
DETECTOR
3RD. VIDEO
I.F. AMP.
B+
b'
-------------
FROM
VIDEO
DETECTOR
AG.C.
lsr.
v ....
1D
_
E
_
O
_
A
_
M_P. _____
�ro
2ND.
VIDEO AMP.
KEYED AG.C.
•E"' C-1 , ,
�FLYBACK PULSE
47K
47K
�
llMF
560
B+
K
47K
680
B++
B+
B++
J
4MF
Figure 12-Video I.F. system and Keyed A.G.C. circuit
Since the trouble has been isolated to the video 1.F. stages we will now
examine each stage in turn to locate the difficulty.
Inject I.F. signal at point B which is the grid of the third video I.F.
amplifier. We now observe on the screen that the picture appears to be normal.
That is it is of the proper phase and is in sync. Notice that this stage is
not controlled by A.G.C. The signal might be a little weak since very
little gain is obtained using only one stage of video I.F. amplification. We
now move our I.F. injection signal to point C, (the grid of the 2nd I.F.
Amplifier) and again observe the result on the receiver picture tube. We
now see that the receiver display is negative and out of sync. The trouble
apparently is in the second video I.F. stage. Examination of the schematic
of Fig. 12 will show that both the second I.F. stage and the first I.F. stage
are subject to the controlling action of A.G.C. voltage.
23
Содержание 1076
Страница 2: ...Figure 1 Front Panel Controls...
Страница 61: ...TMOtl I...
Страница 62: ...Tll10 ff I...
Страница 63: ...Tll I Off I...
Страница 64: ...T Off...