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Date Posted: 18:59:45 11/11/01 Sun
Author: star
Subject: Re: 3CHIP HELP NEEDED : Vertical Sync Missing!!!
In reply to: Tom 's message, "Re: 3CHIP HELP NEEDED : Vertical Sync Missing!!!" on 11:59:31 11/10/01 Sat



>What takes the place of the missing vertical sync? Is
>the whole VBI missing and replaced by nothing? What
>is the dc level of this nothing during the VBI?

Tom,

Thanks for the info. I am using a Tek 500Mhz scope which has TV trigger to look at the video signal. The scope is capable of triggering on the frame, so there is something there in place of the VBI. However it looks nothing like pre or post equalizing pulses/vertical sync. I looks like everything in the VBI section(pre or post equalizing pulses/vertical sync) is a varying sine wave with some positive and negative peaks. The horizontal syncs look like they are dc lowered. Also, the horizontal sync level is lower than the black level, and the burst seems as though it is at the same level as the sync level. Everything else seems okay. If you are interested and would like to see them(VBI,horiz sync) I have captured them from the scope.

Thanks for the help.

>
>The 3chip doesn't lock to the VBI, it only locks to
>the horizontal sync. It uses line 6 to tell where it
>is in the frame. The absence of any vertical pulses
>should be detectable and can be used just like line 6.
> You need to know exactly what your scrambled sync
>looks like and rewrite the code to detect missing VBI
>pulses.

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