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Scramble my electrons and call me a SCART lead....

 
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Scramble my electrons and call me a SCART lead....

Post by Katie Bush » Fri May 27, 2016 5:08 pm

Here's a slightly different story, and I'd be interested to hear what others might think on the matter.

When I first got my SKY+HD box, I still didn't have a an HD set to connect with, so as you do, I used the SCART socket (there is only one on these newfangled boxes).

Back in the day of the original 'Digi-Box' you had two SCARTs, one connected direct to the TV set, and the second to your video recorder, or in my case, DVD recorder.. This seemed a neat arrangement because it kept the TV and video recorder outputs separate, and to my mind at least, gave a single, clean signal path to the TV.

With the +HD box, I had to run the single output first to the DVD recorder, and from there to the TV - that means two leads, and four plugs/sockets to do their worst.

Now all this was about three years ago, and I have say the picture quality was never that fantastic, and to add insult to injury, the audio always seemed a bit low.

The part I can't quite figure is this, Over space of the last three years the picture quality has degraded beyond belief, lacking detail, looking 'smeary' and taking on a progressively worsening sepia colour tone - not too bad when watching black and white films from WW1, but not at all good on anything in colour, and giving a coppery colour to the dark areas of the picture.

More recently, the TV began making a raspy buzzing noise from the speakers that varied with picture content - more white, more buzz - caption buzz?!

Personally, I thought it was just the old telly (1995-ish Sony wide Trinitron) slowly giving up the ghost.. The poor picture might have been dismissed as the CRT going low emission, but the caption buzz? Via SCART? It didn't make any sense.. So full of enthusiasm, and spurred on by the cat slipping off the back of the telly and falling amongst the 'telephone exchange' of cables, disconnecting some as he went.. I had no choice but to get in there and reconnect the cables - I had hoped that just maybe, wriggling the plugs might show an improvement, but it didn't.

I have no idea why, but for some reason I decided to disconnect the 'SKY to DVD recorder' lead and reverse the connection (swap ends).. The result was absolutely astounding.. I've never seen better pictures from this receiver-recorder-TV combination.. The sepia colour is gone, the picture is pin sharp and with unbelievably vibrant colour - no smear, and the caption buzz is 100% gone.

Now, put the SCART lead back to how it was and the problems reappear.. Put it back in the 'reversed' way round and all is perfect - Why?

I've come across theories among audiophiles that claim speaker cables should only ever be connected one way round because of the effects of electrons flowing in one direction along the conductors - yeah, right! And, if you're wealthy enough (gullible enough) you can by pre-polarised speaker cables - :aaj ..... Okay, so I have a pre-stressed SCART lead! :aak

Go on then, any ideas why my setup was so afflicted by a cable?

Marion

P.S.
SCART = Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs

I guess that explains everything? - :aak :aal

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Rebel Rafter » Fri May 27, 2016 7:20 pm

Hi, form RR. I think I know the answer to this one. I tried replying earlier but my pc casually screwed up on me and casually trashed my post. First of all what quality of scart lead are you using? I think it must be one of the cheapie ones with no individual screening which is really essential to prevent this very kind of fault happening. The signal from the sky to the DVD will be CVBS and scart leads have a wire for this in each direction if it's a fully wired lead which I assume it is. The CVBS leaves one end at pin 19 and goes in to the socket at pin 20 at the other end, and vice versa. So I think you've got some bleed over from the CVBS wire in one direction to the audio wires in the same direction as the audio wires also run in both directions just like the CVBS. And by the looks of it you're only using the lead in one direction so this would explain why it corrects when you turn it around, as when you do that you're using the wires from the other direction and thereby disconnecting the faulty ones. I think you'll find the buzz is caused by field sync. pulses bleeding over to the audio wires. You should try using only individually screened scart leads which is what I always do with my set up. Or if you're only using one direction why not get some suitable mini screened cable, maplin have some miniature 75 ohm coax just right for the job, and some for the audio and make your own lead, that should solve it for good. RR.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Katie Bush » Fri May 27, 2016 7:51 pm

Hello rebel,

Aha.... I should have explained better.. :ccg

The signals - CVBS? Good grief, does anyone use that?.... Sorry, no.. It's RGB all the way from the SKY box to the DVD-R and on to the TV.. I seriously couldn't be doing with anything as poor as CVBS.

The DVD-R extracts its signals for recording from the RGBs as they loop through to the output to the TV.. Similarly, the DVD playback output is also RGB, which I must admit gives outstanding performance on this ancient telly.

The SCART lead is of the old school, as thick as a garden hose (it came with the original 'Digi-Box') and is individually screened construction - definitely not one the later "£1.99 from Wilko" variety.

the kit might be old, but is quality.. Original SKY box was Panasonic, DVD-R is Sony a HDD/DVD and the telly, as has already been said is also Sony.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by sideband » Fri May 27, 2016 8:08 pm

Katie Bush wrote:Hello rebel,

Aha.... I should have explained better.. :ccg

The signals - CVBS? Good grief, does anyone use that?.... Sorry, no.. It's RGB all the way from the SKY box to the DVD-R and on to the TV.. I seriously couldn't be doing with anything as poor as CVBS.



Ahhh yes but....the composite video signal still uses pin 20 for sync so you could still have video/sync signals messing up the audio. RGB is fed on separate pins (I forget which ones now) but the sync is still via pin 20.

Pin 16 is RGB status switching and pin 8 is video status switching.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Rebel Rafter » Fri May 27, 2016 8:17 pm

Hi, from RR. Really, that's news to me. I didn't know you could get any kind of video recording machine with RGB at the INPUT! I've never seen one like that, I know they have RGB and other various options at the o/p. I have to use RGB to watch my Katherine Jenkins DVD's as the only ones I could get my mits on were NTSC as all the pal ones were sold out all over the UK. Woolworths had to order me some from Jersey of all places and they must've been export stock for the US or Canada or Japan or the West Indies. I can't imagine why it only works one way when the RGB only runs one way in a scart lead. I think you'll just have to get another lead and try dissecting the faulty one to find out what's gone wrong, assuming it is the lead that's causing it. It'll be interesting and perhaps a bit of a revelation to find out what the real cause is. I've never seen this kind of fault with a proper scart lead, I know it can happen with cheap trashy ones because of the lack of screening between wires. Don't forget that even with RGB there still has to be sync. and this is provided by the CVBS and there could still be some bleed over between it and the audio leads. Trying examining the lead for any damage. RR.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Katie Bush » Fri May 27, 2016 8:18 pm

Hi Rich,

Ah, yes... I see where you're coming from... No "syncs on green" then? How does my projector, which is only ever connected via three RGBs (individual BNC connectors) derive its syncs from a SKY box, then?

Back to the SCART.. I opened the plugs at both ends, and although very 'busy' in there, I couldn't find any evidence of broken wiring or soldered joints.. Granted, I didn't check it out with a meter.. What mystifies me most though, is the gradual deterioration.. I could understand a sudden onset if a connection was lost, but these symptoms developed over a period of time, or at least, deteriorated over time.

Marion

 
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Re: Scramble my electrons and call me a SCART lead....

Post by sideband » Fri May 27, 2016 8:30 pm

Katie Bush wrote:Hi Rich,

Ah, yes... I see where you're coming from... No "syncs on green" then? How does my projector, which is only ever connected via three RGBs (individual BNC connectors) derive its syncs from a SKY box, then?



Dunno! Maybe the SKY box outputs Sync on Green as well (via Phono)?. That won't work Scart to Scart though. Sync on green was never part of the Scart specification.

I would think that your projector will also accept output from a video card from a PC so sync on green is probably a requirement.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Katie Bush » Fri May 27, 2016 8:46 pm

sideband wrote:
I would think that your projector will also accept output from a video card from a PC so sync on green is probably a requirement.


Hi Rich,

That, it certainly does. :aad Via a "VGA to RGB" patch lead.. Using the same input BNCs, the projector will accept TV resolutions, and goes at least as high as 1024 x 768 - oft used for "Friday night is movie night" during the Summer months (300" 16:9), brilliant!

Marion

 
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Re: Scramble my electrons and call me a SCART lead....

Post by ntscuser » Fri May 27, 2016 9:54 pm

Rebel Rafter wrote:Hi, from RR. Really, that's news to me. I didn't know you could get any kind of video recording machine with RGB at the INPUT! I've never seen one like that, I know they have RGB and other various options at the o/p.


Panasonic DVD recorders accept RGB input at PAL frame rate (but oddly only composite video input for NTSC signals). I used to record RGB signals from my Freeview set top box to a DVD-RAM disc with no noticeable loss of picture quality. Setting two separate timers was a real hassle though.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Rebel Rafter » Fri May 27, 2016 10:13 pm

Hi, from RR. How does "VGA to RGB" work, I know the RGB o/p on VGA is to scart standard, i.e. 0.7 vp-p in to 75 ohm, but what about the sync.? VGA sync. runs at a totally unrelated frequency to that of PAL, and it has separate horizontal and vertical sync., while combining it is easy enough, I once built a little module with a CMOS logic chip once for that purpose but what about the frequency? do you have to use special software on the computer to convert it, or do you need a fancy circuit, possibly using a microprocessor with custom software? RR.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by ntscuser » Fri May 27, 2016 10:36 pm

Rebel Rafter wrote:Hi, from RR. How does "VGA to RGB" work


There's an explanation here: http://www.nexusuk.org/projects/vga2scart/

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Katie Bush » Fri May 27, 2016 10:44 pm

That I think, is where we start to get into the world of wizardry and witchcraft.. :aab

All I can say is, the cable I use has a standard VGA monitor plug at one end, and terminates in three separate (RGB) BNC plugs at the other.. The projector is ex lecture hall kit, bought via the web, and seems quite happy to sync up with everything I've connected to it thus far.. It likes TV standard, and likes 1024 x 768 even better. :aad This is why I was wondering about the "SOG".. The projector (also Sony) has five (I think) input BNCs - RGB (also labelled YPbPr) but I'm not certain what the others are labelled as.. In the set up menu, it has an option for 'sync on green' and another sync option.

Let's just say, it was set up about five years ago, and all I do now is plug n' play...

 
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Re: Scramble my electrons and call me a SCART lead....

Post by sideband » Sat May 28, 2016 8:17 am

Rebel Rafter wrote:Hi, from RR. Really, that's news to me. I didn't know you could get any kind of video recording machine with RGB at the INPUT! I've never seen one like that, I know they have RGB and other various options at the o/p.


As far as I know, most recorders that allow RGB input actually convert it to CVBS for recording purposes and then back to RGB for output. It will also be available as a standard CVBS output as well. It's done that way to ensure compatibility with other machines.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Cathovisor » Sat May 28, 2016 11:08 am

Not sure about that, Rich; some machines will matrix to component and record that...

 
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Re: Scramble my electrons and call me a SCART lead....

Post by Rebel Rafter » Sat May 28, 2016 11:18 am

Hi, from RR. YPbPr is also known as "component" video, a bit like RGB but the green channel doubles as a CVBS input and for this reason is sometimes coloured both green and yellow, that's how it is on my mate's humungous great big Panasonic flat screen contraption. I think that's why it has "Y" as a prefix, Y meaning luminance, which also carries sync. as well as green when using an RGB connection. I don't know how it's all processed once it gets inside whatever it's feeding into. I think component video is designed so you can use either RGB or CVBS on the same connector(s), but when using RGB obviously there must be sync. on the green channel so whatever's feeding it would have to provide it. RR.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by sideband » Sat May 28, 2016 4:25 pm

Cathovisor wrote:Not sure about that, Rich; some machines will matrix to component and record that...

Well that's certainly a better way of doing it.

 
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Re: Scramble my electrons and call me a SCART lead....

Post by davegsm82 » Sat May 28, 2016 10:52 pm

Could the noise be somehow related to mains leakage on one of the devices causing transformer action in the SCART cables?

I've seen this happen when the antenna was being earthed by another Tv that it was split from, current travelling from a leaky SKY box, through the SCART, through the TV, out the antenna socket along the wire to the Yagi, back down another coax to another TV which had an earth connection through it's own SCART (or might have been an HDMI) and out to ground via that device's earthed, 12V in-line power supply which had a Cloverleaf type mains connector.

I only noticed the cause of the fault when I saw the spark as I plugged in the belling-Lee connector on the back. :elc:

Dave.


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