Re: SCART leads

[Keith Doxey <ukha@xxxxxxx>]

Quoting tannedblondbloke <tannedblondbloke@xxxxxxx>:

> Over the holidays I added some SCART leads to my sister's home cinema
> set-up.  Each box (digi, video and DVD) now has a SCART lead to the
> telly, and there is a SCART lead from digi to video.
>
> The TV has now started misbehaving.  Say you select the digibox on
> the telly.  That's fine for a few a minutes and it sudenly switches
> to video.  A few minutes later, it suddenly switches back to digi
> again.  I think I read somewhere that it is down to one of the pins
> on the SCART - when it goes high, it forces the TV to select the
> source corresponding to that SCART, and I guess the telly gets
> confused if a high signal is present for multiple sources.

SCART Switching is implemented differently by different manufacturers.

Pin 8 is the pin used to grab control of the TV, some sets detect the
positive
going edge of the signal to signify an active source, others detect the
high
level to signify an active source.

Often there is a priority associated with the AV inputs, in the case of my
TV,
AV1 will always override any other source meaning that any changes on AV2
will
be ignored whilst AV1 is high. This in itself can lead to strange effects
eg...

Viewing normal TV - AV1 goes high - Set switches to AV1
then AV2 goes high - ignored because AV1 is high.
Then turn of source for AV1, set does not drop back to TV but now senses
the
AV2 input and switches to that.

As I said, each manufacturer has a different way they prefer to do things.

What I dont understand is why your inputs keep changing. A VCR should ONLY
take
Pin 8 high when in playback mode or in the case of some VCR's when the Menu
is
selected for programming ( because obviously you would want to see what you
were doing!). Whilst on Record, Stop, FF, REW or Standby is should NOT grab
control.

You dont say which inputs are connected to which source and it could be a
priority thing but I dont see why a VCR would keep grabbing control.

One thing that springs to mind is something that used to happen with my
analog
satellite systems (PACE). Turning the Satellite on would correctly grab the
TV
but we didnt always want to watch it on the main TV so would press BBC1 etc
to
return to normal viewing. We could than watch satellite in any other
room...
BUT... IF we changed channel on the satellite it would DROP PIN 8 AND
RE-ASSERT
ITSELF thereby grabbing the main TV again.

Do you have any sort of "Red Dot Remover" device connected to the
Digibox that
repeatedly sends a "Backup" command to remove the red dot. ?It
could be that
this is causing a change to pin 8 momentarily giving rise to the effect
that
you are seeing. Is there a regular timing to the events?

>
> As I see it there are potentially 3 solutions:
>
> The simplest, and what I have told them to do for now, is to make
> sure that any boxes not being used are put into standby.  This is not
> a long term solution, as for example, this won't help if you want to
> watch one source and video another, as all 3 boxes would be on.

Would be very helpful if you wanted to watch in another room either :-(

>
> The ideal solution would be if there is a "soft" method ie
if there
> is a menu option somewhere to disable this behaviour - I don't think
> the TV - a Sony - supports this, but I don't have the manual to hand,
> it's at my sister's.

Difficult to say but highly unlikely. Depends on manufacturer.

> This leaves a somewhat more drastic method - removing the offending
> pin from the SCART leads.  This raises some questions - which pin?
> Will it cause complications? And what physically is the best way to
> achieve this without damaging the rest of the lead?
>

Remove Pin 8 from the SCART lead. Looking from the pin side of the plug you
will see a small tang that holds the pin in place. Gently depress this and
you
can push the pin back into the body of the plug, once removed from the
housing
wrap it in insulating tape so that you can restore it to normal operation
if
required.

http://www.diyha.co.uk/electronics/scart.html
for the pinout.

Before you try that, see if choosing different AV inputs solves the
problem.

Hope that helps.

Keith

www.diyha.co.uk
www.kat5.tv

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