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Date Posted: 20:55:58 01/17/02 Thu
Author: EC
Subject: Potter - strange Pal System

Hi Potter,

you mentioned in another posting that
your system is a little different, so
maybe you can guess what happens here:

System is PAL-M: 15734Hz and 59.93Hz.
Video inversion is default.

Hsync is present, you just have to
re-invert the video.

Vertical sync is absent and the 3chip,
even when locked, cannot put it back
perfectly. Audio is normal and video
inversion is active only in a few
channels, but the 3chip could not
detect the data at line 18. Seems like
it never found line 18, because there's
some allien pulse that triggers the
edge detectors at the wrong time.

Something messes up with the Vsync pulse
even in the not-scrambled channels. The
picture will stabilize in the "open"
channels but the OSD of the TV cannot
display messages correctly because the
Vsync bonces up and down.

I tried different codes in the 3-chip
and gave-up. The best solution was a
simple Vsync generator, it works better.
But there's this an interference that
randomly shakes the VBI... It don't look
like a burst pulse, because that would
interfere with the Hsync as well. I get
a stable Hsync and perfect colors.

I was wondering if cable modem signals have
something to do with this problem, because
the AGC is also affected.

What do you think?

EC

PS: sorry, no osciloscope at home and
no cable at work. System is GI 5507

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