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General Category => Technical Support => Hardware related => Topic started by: John Mitchell on 00:01, 12 January 15

Title: Scart to LCD TV
Post by: John Mitchell on 00:01, 12 January 15
I built a scart lead for my 6128.  It works perfectly with a CRT TV I have but none of my LCDs work quite right.  I understand there's some issues with LCDs but it seems so close I thought someone might have some ideas.


You can see a short video in youtube (CPC Scart to LCD not quite right - YouTube (https://www.youtube.com/watch?v=Qo_onhWrOCU)) or below is a picture of what it looks like.


I do have an RGB to s-video/composite converter on its way but I'd rather get it working without any extra boxes.


(http://i247.photobucket.com/albums/gg134/neufena/2015-01-11185750.jpg)

Title: Re: Scart to LCD TV
Post by: Bryce on 10:28, 12 January 15
You're using a switchmode power supply aren't you? Try using a "proper" powersupply and see if those problems are still there.

Bryce.
Title: Re: Scart to LCD TV
Post by: TFM on 19:57, 12 January 15
A problem with the input selector? If I push a button on my monitor, then the picture looks the same.
Title: Re: Scart to LCD TV
Post by: fgbrain on 22:11, 12 January 15
Recently I changed my old SCART cable to plug into my new LG ips TVmonitor 23"...
I just added a capacitor, as suggested in the alternative wiring in the wiki page..
Picture is crystal clear now.. awesome!


Hope this helps you
Title: Re: Scart to LCD TV
Post by: Bryce on 23:23, 12 January 15
The capacitor in my alternative schematic holds the Source input at the correct level without needing a battery. The voltage is created by charging the capacitor with the LUM signal. It will work on any TV that sticks to the SCART standard. But it doesn't really do anything to improve the picture, other than the fact that some LCD TVs will flicker or keep showing the OSD, because they keep "refinding" the signal, if that voltage is missing.

Bryce.
Title: Re: Scart to LCD TV
Post by: chinnyhill10 on 02:41, 13 January 15
The capacitor in my alternative schematic holds the Source input at the correct level without needing a battery. The voltage is created by charging the capacitor with the LUM signal. It will work on any TV that sticks to the SCART standard. But it doesn't really do anything to improve the picture, other than the fact that some LCD TVs will flicker or keep showing the OSD, because they keep "refinding" the signal, if that voltage is missing.

Bryce.


That's interesting.


I use various bits of kit to convert RGB to Component that I can capture for ChinnyVision. Obv RGV capture kit doesn't exist so it has to be done this way.


Some devices show the CPC's output as black and white. Would this mod to my CPC's cable fix this? And if so is there a guide for dummies (i.e. me). Eg buy a certain cap and wire it in a certain way (e.g. diagram + a photo so stupid people like me have something easy to follow).


Cheers.
Title: Re: Scart to LCD TV
Post by: Bryce on 10:29, 13 January 15
The capacitor is only useful for connecting to a real SCART input. For general RGB it won't help much. All the details (Diagram etc) are here: TV SCART cable - CPCWiki (http://www.cpcwiki.eu/index.php/TV_SCART_cable#Alternative_RGB_Wiring) (Dummied down as much as I could :D).

What device do you use for capturing the videos? And which ones give you only B&W?

Bryce.
Title: Re: Scart to LCD TV
Post by: chinnyhill10 on 14:08, 13 January 15

What device do you use for capturing the videos? And which ones give you only B&W?

Bryce.


I have to convert RGB to component in order to capture it. This should be simple but is anything but due to the wide variety of systems I cover.


Eg I have a Panasonic DVD recorder which is fine with the CPC, Megadrive, Amiga, BBC and others. But the same machine hates my Master System, Spectrum (Amstrad models) and SNES. Part of this is because the Panasonic has an AGC which you can't turn off and it dislikes out of spec signals.


So I have purchased a number of other DVD recorders but none of them work for all machines. The latest is a Pioneer model which works wonderfully with most systems but presents a black and white picture for the CPC and no picture at all for the Spectrum (Amstrad models). Shame as it appears to be the best unit and has wonderfully adjustable picture controls (including being able to turn off the AGC)


Note I don't recorder to the DVD recorder. The signal passes through the machine for the conversion to component that I need. It doesn't go anywhere near MPEG or a disc. All I need is a component de-interlaced 50fps sign.


It's complicated and expensive but I think the quality justifies it.
Title: Re: Scart to LCD TV
Post by: Bryce on 14:35, 13 January 15
I've noticed that problem with the "Amstrad Spectrum" machines too. If I connect my S-Video adpter to my +3 the picture flickers as if the TV can't sync to it. I've never taken the time to find out why. But when I get a chance to analyse the signal I'll let you know what's missing and how to correct it. I assume it's a problem with the Sync frequency or levels that the Spectrum outputs.
Not sure about the Master system though, I don't have one.

Bryce.
Title: Re: Scart to LCD TV
Post by: chinnyhill10 on 14:43, 13 January 15
I've noticed that problem with the "Amstrad Spectrum" machines too. If I connect my S-Video adpter to my +3 the picture flickers as if the TV can't sync to it. I've never taken the time to find out why. But when I get a chance to analyse the signal I'll let you know what's missing and how to correct it. I assume it's a problem with the Sync frequency or levels that the Spectrum outputs.
Not sure about the Master system though, I don't have one.

Bryce.


The Panasonic machine is known to be troublesome with some sources due to the AGC. The Master System is fine on the Pioneer.
Title: Re: Scart to LCD TV
Post by: Bryce on 15:40, 13 January 15
AGC (Automatic Gain Control for those who are saying "What's that?") might mess the colours up, but shouldn't cause sync flicker or a completely blank page. The type and method of PLL (Phase locked loop) used in a TV is what usually causes most problems. Some TVs can match any (most) input frequencies, but others have pre-defined frequencies and if the computer doesn't have an output close enough to the standard, then the TV can't match the input and keeps trying to re-adjust. This happens in two ways. On some TVs the picture will slowly drift to one side and then "snap" back to the other side. On other TVs the picture will appear stable but then seem to reset (picture disappears for a second and returns) every few seconds. CRTs never had this problem as the PLL circuitry was purely analogue, whereas LCD TVs (and recorders etc) are doing this with digital circuitry.
My Panasonic TV gives a great picture quality for most retro stuff, so it's not brand dependent, more chipset. It can also depend on the particular input port. I have a JVC LCD TV which is great on S-Video and terrible on SCART.

Bryce.
Title: Re: Scart to LCD TV
Post by: John Mitchell on 21:01, 13 January 15
Thanks for the tip about the switched mode power supply, it seems that was the problem.  I powered the CPCP from the original monitor, works perfectly.  I was using a cheap hard drive power supply, now to search out something else to use.


I have an old PC supply lying around, maybe that will do for now.
Title: Re: Scart to LCD TV
Post by: Bryce on 22:01, 13 January 15
Cool, easy fix. The pattern on your TV was classic SMPSU ripple/noise interference. PC Supplies are actually switchmode too, but they are well filtered (better than a chinese HD PSU at least), so it shouldn't give the same problems.

Bryce.
Title: Re: Scart to LCD TV
Post by: John Mitchell on 23:02, 13 January 15
Just tested, works perfectly. Might even be able to power the LCD from the same supply (it's 12v) so double win.
Title: Re: Scart to LCD TV
Post by: Bryce on 23:05, 13 January 15
Yeah, that shouldn't be a problem. Just a pity the PC PSUs are such ugly blocks of metal. Hide it well.

Bryce.