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TELETEXT-DECODER ADJUSTMENT
The teletext p.c.b. requires three alignment operations which are all
relevant to the video input processor SAA 5030.
These alignment operations eliminate influence of tolerances both Of
video input processor and of its peripherical components.
The adjustment procedure need not be repeated any more until no
substitutions are carried out and until the same video input
processor is used.
1. Adjustment of the chronological position (phase) of synchro. pulses
the video input processor SAA 5030 is adjuted through trimmer PlT.
The video signal phase (TP8), and in particular the portion including
the vertical synchro. signal must be compared on the oscilloscope
against the output signal taken from contact 13 of IC SAA 5030
The trimmer is adjusted so as to delay the leading edge of the video
signal pulse (on contact 13) 48 2 5 )H with reference to the start
of the vertical synchro. signal (wide pulses).
This position is shown in Fig. 1.
The leading edge of the vertical synchro. pulse must thus be at 3/4
of line on line 1 and at a l/4 of line on line 314 of video signal.
Video input signal
Vertical synchro. pulse
from contact 13 of
IC SAA 5030
U
1 -
Fig.
Adjustment for correct positioning of
vertical synchro. pulse.
-29-
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