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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

scart switching blanks video signal



 
 
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  #1  
Old January 27th 07, 04:15 PM posted to uk.tech.digital-tv
josh
external usenet poster
 
Posts: 1
Default scart switching blanks video signal

First, apologies if this question has been answered already on this
newsgroup somewhere.

I have three scart imputs in the back of my TV but four outputs from boxes.
I bought a two-input switchable junction box from Maplin, plugged cables
from Sky box and DVD recorder into it , and plugged the output cable into
the TV. Problem sorted, I thought naively.

With signals coming from two sources to the switch box, I naturally thought
that as I pressed the button in and out I would see first one and then the
other TV progamme. Alas, the signal from the sky box was fine but the
signal from the DVD recorder had sound but no vision.

Despite tests the problem remained, the sky box seeming to be dominant and
suppressing any other video signal. I gave the whole thing up, abandoned
the switch box and resorted to plugging the scart male outputs manually into
one of those simple blocks with femail scart imputs at opposite ends.
Hardly an advanced solution technically!

That would have been that, but last night a friend was describing his scart
connections to a similar but larger junction box, and to my surprise brought
up exactly the same problem of lost video signals.

So what is going on? And more specifically, what goes on in these scart
switch boxes? We began to suspect that the box doesn't switch all 20 of the
lines, or there would surely be an almighty clunking noise!

Josh


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  #2  
Old January 27th 07, 04:36 PM posted to uk.tech.digital-tv
R. Mark Clayton
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Posts: 1,331
Default scart switching blanks video signal


"josh" wrote in message
news
First, apologies if this question has been answered already on this
newsgroup somewhere.

I have three scart imputs in the back of my TV but four outputs from
boxes. I bought a two-input switchable junction box from Maplin, plugged
cables from Sky box and DVD recorder into it , and plugged the output
cable into the TV. Problem sorted, I thought naively.

With signals coming from two sources to the switch box, I naturally
thought that as I pressed the button in and out I would see first one and
then the other TV progamme. Alas, the signal from the sky box was fine
but the signal from the DVD recorder had sound but no vision.

Despite tests the problem remained, the sky box seeming to be dominant
and suppressing any other video signal. I gave the whole thing up,
abandoned the switch box and resorted to plugging the scart male outputs
manually into one of those simple blocks with femail scart imputs at
opposite ends. Hardly an advanced solution technically!

That would have been that, but last night a friend was describing his
scart connections to a similar but larger junction box, and to my surprise
brought up exactly the same problem of lost video signals.

So what is going on? And more specifically, what goes on in these scart
switch boxes? We began to suspect that the box doesn't switch all 20 of
the lines, or there would surely be an almighty clunking noise!

Josh


The $ky box asserts the RGB present signal, which for some reason is passed
through these Maplin switches. OTOH it switches the actual RGB lines, so
the TV displays this input and no picture appears.

If possible set the DVD recorder to output RGB.


  #3  
Old January 27th 07, 09:11 PM posted to uk.tech.digital-tv
Colin Stamp
external usenet poster
 
Posts: 369
Default scart switching blanks video signal

On Sat, 27 Jan 2007 17:15:08 -0000, "josh"
wrote:

First, apologies if this question has been answered already on this
newsgroup somewhere.

I have three scart imputs in the back of my TV but four outputs from boxes.
I bought a two-input switchable junction box from Maplin, plugged cables
from Sky box and DVD recorder into it , and plugged the output cable into
the TV. Problem sorted, I thought naively.

With signals coming from two sources to the switch box, I naturally thought
that as I pressed the button in and out I would see first one and then the
other TV progamme. Alas, the signal from the sky box was fine but the
signal from the DVD recorder had sound but no vision.

Despite tests the problem remained, the sky box seeming to be dominant and
suppressing any other video signal. I gave the whole thing up, abandoned
the switch box and resorted to plugging the scart male outputs manually into
one of those simple blocks with femail scart imputs at opposite ends.
Hardly an advanced solution technically!

That would have been that, but last night a friend was describing his scart
connections to a similar but larger junction box, and to my surprise brought
up exactly the same problem of lost video signals.

So what is going on? And more specifically, what goes on in these scart
switch boxes? We began to suspect that the box doesn't switch all 20 of the
lines, or there would surely be an almighty clunking noise!

Josh


Surely, at least one of the four boxes will have two SCARTs? That
should allow you to daisy-chain in one of the other boxes. Then you'd
only need three SCARTs on the telly, and the switching would be
automatic to-boot.

Cheers,

Colin.
  #4  
Old January 27th 07, 09:18 PM posted to uk.tech.digital-tv
Roderick Stewart
external usenet poster
 
Posts: 1,267
Default scart switching blanks video signal

On Sat, 27 Jan 2007 17:15:08 -0000, "josh"
wrote:

I have three scart imputs in the back of my TV but four outputs from boxes.
I bought a two-input switchable junction box from Maplin, plugged cables
from Sky box and DVD recorder into it , and plugged the output cable into
the TV. Problem sorted, I thought naively.

With signals coming from two sources to the switch box, I naturally thought
that as I pressed the button in and out I would see first one and then the
other TV progamme. Alas, the signal from the sky box was fine but the
signal from the DVD recorder had sound but no vision.

Despite tests the problem remained, the sky box seeming to be dominant and
suppressing any other video signal. I gave the whole thing up, abandoned
the switch box and resorted to plugging the scart male outputs manually into
one of those simple blocks with femail scart imputs at opposite ends.
Hardly an advanced solution technically!

That would have been that, but last night a friend was describing his scart
connections to a similar but larger junction box, and to my surprise brought
up exactly the same problem of lost video signals.

So what is going on? And more specifically, what goes on in these scart
switch boxes? We began to suspect that the box doesn't switch all 20 of the
lines, or there would surely be an almighty clunking noise!


You're right. They don't all switch all the signals, especially the
cheap two input ones. Sometimes they don't even carry all the signals,
so if you've switched your DVD player to RGB output the composite
signal won't be there and you'll get a blank screen as you describe.
Some of them don't switch at all but just mix the signals, relying on
you powering the various items of equipment on and off as you need
them. Sometimes the two audio signals are shorted together so you only
get mono sound (why? to save one wire?). I even found a weird one
where the Pin 8 switching signal wasn't switched, but the two inputs
were fed through diodes, so that the TV would switch to widescreen if
*either* input was widescreen, even if it wasn't the one you were
watching. It took a bit of detective work to trace that last one and I
ended up cutting tracks on the circuit board as a temporary bodge, but
the only real solution to this is to get a proper fully wired SCART
switcher, making sure it is described as such and can switch RGB
before you buy it. They're more expensive of course, but if you want
something doing properly you generally do have to pay.

Rod.
 




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