Author Topic: Another SCART topic...but with a difference  (Read 10130 times)

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Offline Shredder11

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Another SCART topic...but with a difference
« on: 19:54, 07 July 10 »
I recently bought some SCART cables from the much respected Ebay shop http://www.retrocomputershack.com for my CPC6128, Spectrum +3 128K and Commodore C64.  The only cable that worked was the C64 cable, the other two gave a clear but incorrect output.  I tried all my computers and cables on various things including a normal CRT TV, a VGA monitor via the excellent Supera Color HD video conversion box http://www.dealextreme.com/details.dx/sku.15178 .  I got the exact same results with each screen and method used.  I've included a few photos to highlight what results I get, additionally I have shown the Spectrum results both with SCART and RF cable methods.  As you can see with the Spectrum I get a perfect output with RF, but a very dark colourless output with the SCART.  I do not have an RF output for my CPC6128 yet (I have a MP-1 modulator on the way), but the SCART gives a similar result as the Spectrum.  Seeing as these two computers are both made by Amstrad and share some components etc, I expect my problem could be the same for both.
 
I've not contacted the seller yet as I wanted to find out if I am doing something wrong myself first.  Regarding powering both computers, I am using the correct voltages and polarities to the right sockets and both computers function as they should.  So if anyone can shed a little insight into what else I could try, I would be grateful.
Amstrad CPC6128, 3.5" Ext' Floppy, SD HxC Floppy Emulator

Offline MacDeath

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Re: Another SCART topic...but with a difference
« Reply #1 on: 20:13, 07 July 10 »
What about the setting of the TV ?

Tried the RGB setting, then the Video or S-video settings ? or whatever it can manage ?

Exemple : my old TV has to be on Video/S-Video setting instead of RGB in order to use my freebox (internet supplier's TV box) or else picture is red/pink...

But so true : getting decent modern monitors running 8/16 bits machines is sort of a nightmare, mostly because now every screens are 16/9...

Offline Pentagon

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Re: Another SCART topic...but with a difference
« Reply #2 on: 20:14, 07 July 10 »
I also have two older Televisions with a scart and they dont work with a CPC scart cable. I got the same results like you. I think not all Televisions with Scart Connector can do a RGB signal. Some just have Fbas Video and others just S-Video.

On my bigger television the left scart connector is full RGB and the cpc is sharp and colorful and at the same TV the other scart cant do RGB but S-Video. So i think your Television Scart cant do RGB correct or you need to setup RGB in menu.


Kindly Regards
Tom

Offline Shredder11

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Re: Another SCART topic...but with a difference
« Reply #3 on: 21:25, 07 July 10 »
I've tried all the available connections on both my TV, i.e. both SCART inputs and composite inputs and in the Spectrums case the RF input (that worked).  My 28" CRT TV is a Philips from 2003 and I have checked the settings, but there is nothing related to RGB.  However I do use a DigiFusion FVRT200 Freeview recording box with the Philips TV and this has output settings for RGB, S-Video and Composite.  When I flick through those three settings on the Freeview box, RGB gives a vibrant, clear and stable picture; S-Video gives a black & white picture and Composite gives a normal colour picture that is slightly wavey and noisey.  Also if I recall correctly the Freeview box when connected to my desktop PC capture card gives a black & white picture when RGB is left selected on the Freeview box, and I have to select S-Video to get an RGB colour picture!  So I suppose I could connect the CPC6128 to my PC capture card as a test.  Another thing I have not tried yet is connecting via my Philips VHS VCR SCART and then back out via SCART or RF.

Retro is never straight forward eh! :D
Amstrad CPC6128, 3.5" Ext' Floppy, SD HxC Floppy Emulator

Offline mr_lou

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Re: Another SCART topic...but with a difference
« Reply #4 on: 22:01, 07 July 10 »
Maybe you can find something useful in this thread.

Offline Shredder11

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Re: Another SCART topic...but with a difference
« Reply #5 on: 22:09, 07 July 10 »
Thanks I have just had a read of that; always good to know as much info as possible on these things!
Amstrad CPC6128, 3.5" Ext' Floppy, SD HxC Floppy Emulator

Offline mr_lou

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Re: Another SCART topic...but with a difference
« Reply #6 on: 22:25, 07 July 10 »
Thanks I have just had a read of that; always good to know as much info as possible on these things!

I'm describing in that thread how I ended up with a signal almost like yours, and Bryce replies that he has made new schematics for a scart that might fix the problem. (Bryce is our local electronics superhero around here).
I never got around to building myself that scart though, but maybe you'll find it useful.

Offline Pentagon

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Re: Another SCART topic...but with a difference
« Reply #7 on: 23:37, 07 July 10 »
There is another trick you can try to get it work. In some rare cases its necessary to switch on Videotext / Teletext and back to the Scart Input Channel. After switching to Teletext you get the color back. But this works mostly for german Grundig TV's.

Else i can check wich wiring shematics i am using at my cable (its self soldered) and post that here. Then you can compare both shematics and maybe fix your cable.

Tom / Pentagon

Offline Bryce

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Re: Another SCART topic...but with a difference
« Reply #8 on: 11:08, 08 July 10 »
Hi Shredder11, (Were there 10 others who came before you?)
         your TV isn't switching to RGB automatically, so the TV is using the composite signals and hence stays B/W. The TV checks for a signal on pin 16 of the SCART, if the signal is there it switches to RGB mode if not it falls back to composite. You'll have to make a slight change to your cable, either adding a small battery to create the signal, or alternatively, I put another battery-less solution here:  http://www.cpcwiki.eu/index.php/TV_SCART_cable

If you choose a battery solution you don't need the 9V battery shown, that's a different signal to switch the TV from HF to SCART (Only needed on TVs without an A/V Button).

You can make a quick check by opening the SCART connector and connecting a 1.5V Battery across pins 16 (Positive) and 18 (Negative), the picture should change immediately to colour.

Bryce.

@Mr_Lou, thanks for the compliments :)
« Last Edit: 12:04, 08 July 10 by Bryce »

Offline Shredder11

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Re: Another SCART topic...but with a difference
« Reply #9 on: 18:32, 08 July 10 »
Thanks Bryce, ten others? God forbid! No it is simply that eleven is my number so to speak for reasons that are daft.

My TV has an A/V button on the remote to choose between the two SCART sockets (presets EXT1 and EXT2) and the other channel mode presets are SVHS (I forget but it probably is composite) and AV (Composite phono socket).

I will try the power pin method you described soon, although this will invalidate my purchase for return purposes but then again...it's only a cable!
Amstrad CPC6128, 3.5" Ext' Floppy, SD HxC Floppy Emulator

Offline Shredder11

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Re: Another SCART topic...but with a difference
« Reply #10 on: 18:09, 11 July 10 »
Right I soldered two wires onto the SCART cable connector; positive to pin 16 and negative to pin 18 as described on the Wiki here.  I connected these two wires to a brand new 1.5V battery and then powered on the CPC6128.  The TV did not produce a colour output, just the same old monochrome and the 1.5V battery became slightly hot after a while.  I tried connecting the battery before and after switching the TV channel to SCART mode.
 
So the next step is to try the non-battery SCART wiring as shown in the Wiki here:
 

 
 
....and if this still does not work, I either need a new TV or an MP-1 modulator.
Amstrad CPC6128, 3.5" Ext' Floppy, SD HxC Floppy Emulator

Offline Cholo

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Re: Another SCART topic...but with a difference
« Reply #11 on: 22:52, 11 July 10 »
How long is the scart cable? It should not be longer than 2-3 metres (5 metres tops), i recall or you will indeed get at black and white image.

Offline Shredder11

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Re: Another SCART topic...but with a difference
« Reply #12 on: 22:55, 11 July 10 »
It was bought from retroshack.com and is approx 1 metres long.
Amstrad CPC6128, 3.5" Ext' Floppy, SD HxC Floppy Emulator

Offline Cholo

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Re: Another SCART topic...but with a difference
« Reply #13 on: 00:27, 12 July 10 »
Well, ive never actually gotten around to solder an amstrad scart cable but i did manage to make a scartcable for a old jamma arcade machine .. and as the machine uses a RGB monitor (and i recall a friend using a cpc monitor as his arcade monitor) then perhaps these schematics will help (and hopefully not confuse to much).

Anyways i made the cable without blanking (no 16 pin connected) and no audio too, so it was just the 3 colour ones and Sync (and the 5 ground ones too). Being lazy and newb at soldering, i bought a cheap 2m normal scartcable and simply cut all the cables in on end and the non-wanted ones at the other. Then just soldered the plug to the cable.

On use: the cable i made only works when its hooked up to "Scart 1" port on my TV (even tho the tv has 2 scart ports). The tv only displays a proper image if i select "RGB" mode on the tv.



Offline bleeper

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Re: Another SCART topic...but with a difference
« Reply #14 on: 16:06, 13 July 10 »
I built my SCART and through some guesswork made it switch to RGB without a battery simply by connecting a couple of the SCART pins together (can't remember which, will check once I'm home). It worked on 2 different brands of TV.
 
Can't understand why the battery would ever be needed?

Offline Bryce

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Re: Another SCART topic...but with a difference
« Reply #15 on: 16:40, 13 July 10 »
The battery is needed because some TVs don't have a manual RGB/Composite button and instead they monitor pin 16 (Fast Blanking) for a Signal to decide which source should be read. The battery provided this signal which "told" the TV to use RGB. The alternative diagram (above) doesn't need the battery because the CPCs pin 4 (sync) provides an adequate signal.

You are correct in saying that you could achieve the same effect by shorting certain pins on the SCART side, but this might not work on every TV, especially modern LCD/Plasma.

Bryce.
« Last Edit: 16:42, 13 July 10 by Bryce »

Offline Cholo

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Re: Another SCART topic...but with a difference
« Reply #16 on: 19:50, 13 July 10 »
Just remembered: Cpcmania has a really nice page about making scart cables for amstrads (with a lot of nice diagrams/pictures):
http://www.cpcmania.com/

Offline Bryce

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Re: Another SCART topic...but with a difference
« Reply #17 on: 21:00, 13 July 10 »
That's a really good tutorial with excellent photos. But I see he has also got power connected to pin 16, just he takes the power from the CPCs 5V rail instead of a 1.5V Battery.

Bryce.

Offline orange

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Re: Another SCART topic...but with a difference
« Reply #18 on: 02:05, 21 July 10 »
so, what pins can be shorted on SCART to get RGB?
I'm using +5V and resistor from CPC PSU, but don't like it,  too many wires :(

i've googled a bit, and one place says to use "100 ohm resistor From pin 8 to 16"

pin 8 should be:
"Status & Aspect Ratio up"

could it be somehow used with compositesync instead?
« Last Edit: 02:11, 21 July 10 by orange »

Offline Bryce

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Re: Another SCART topic...but with a difference
« Reply #19 on: 10:44, 21 July 10 »
Hi Orange,
      What type of TV are you connecting to? And have you tried the battery-less connection here: http://www.cpcwiki.eu/index.php/TV_SCART_cable

Bryce.

Offline orange

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Re: Another SCART topic...but with a difference
« Reply #20 on: 01:36, 23 July 10 »
yeah, i think i wrote about it in another thread.
i'm using plasma TV (panasonic)

one of batteryless solutions works great. the picture has no problems except for a small annoyance: in a top left corner, label 'RGB' shows from time to time (normally it just shows on start for few seconds).
its clearly not getting enough voltage on pin16 constantly.

Offline Bryce

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Re: Another SCART topic...but with a difference
« Reply #21 on: 10:31, 23 July 10 »
Ok, I use a Panasonic Plasma TV too. DEFINITELY DON'T SHORT ANY PINS ON THE PANASONIC SCART!!! It's far from standard and you could really mess up your TV.

If you are determined to keep the connection passive (ie: no battery) you could try adding a small electrolytic capacitor (100µf 16V) across the pins (same pins, just instead of the battery), this might be enough to remove the glitches that cause the RGB label from being displayed.

Bryce.

Offline orange

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Re: Another SCART topic...but with a difference
« Reply #22 on: 16:29, 23 July 10 »
ok, and if capacitor is polarized, use same orientation as batt?
just to be sure, you mean across pins 16 and 18?
« Last Edit: 16:34, 23 July 10 by orange »

Offline Bryce

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Re: Another SCART topic...but with a difference
« Reply #23 on: 16:33, 23 July 10 »
Electrolytic capacitors are polarised, so yes, it should be connected exactly as if it were a small battery (which it is really in that case).

Bryce.

Offline orange

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Re: Another SCART topic...but with a difference
« Reply #24 on: 01:28, 24 July 10 »
um, what about diode? seems like a good idea, to prevent current from going back from caps to CPC ?