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48K COMPOSITE VIDEO infos

SpectrumSpectrum
edited February 2012 in Hardware
I'm not familiar with the Composite Video, so I'm asking help to WOS.
I've got a 48k with Composite Video Mod. I am used to my Toastrack, that I plug to the TV via Scart. Compared with the 128k RGB the 48k Composite Video have faded colours.
I mean: the colours doesn't looks bright as they usually are on the Speccy.
For example, the Basic screen (all white) looks almost yellowish...

It's the same for other Spectrum users with a Composite Video Mod?
Or it's my Speccy that got something wrong?

Thanks for help!
Post edited by Spectrum on

Comments

  • guesserguesser
    edited February 2012
    What version 48k board?

    If it's an issue 2 then it sounds like the presets need twiddling a bit. The colours will drift as the speccy warms up etc, it was quite a crude design.
    My rubbish website including the redrawn Amstrad schematics and the Sinclair Wiki.
  • SpectrumSpectrum
    edited February 2012
    guesser wrote: »
    What version 48k board?

    If it's an issue 2 then it sounds like the presets need twiddling a bit. The colours will drift as the speccy warms up etc, it was quite a crude design.

    Hi! Thanks for your reply!

    How can I check which board is?
    I'm quite ignorant... =P
  • Alien 8Alien 8
    edited February 2012
    Well my 48K machines have always had a rather greyish white screen compared with my +3. I connect the +3 via scart (RGB) and the 48Ks by Composite. The composite image is really very good though, much better than UHF.
  • guesserguesser
    edited February 2012
    Spectrum wrote: »
    Hi! Thanks for your reply!

    How can I check which board is?
    I'm quite ignorant... =P

    It will be printed on the board. along the front iirc.
    My rubbish website including the redrawn Amstrad schematics and the Sinclair Wiki.
  • SpectrumSpectrum
    edited February 2012
    guesser wrote: »
    It will be printed on the board. along the front iirc.

    hmm... but I should open the Speccy... I'm not into that!
    It's so old... I don't want to do that...

    In any case, do you think it need some fix or it will become better just letting the Spectrum warming up?
  • Alien 8Alien 8
    edited February 2012
    Can you see a heat sink through the edge connector slot? If you can, then I don't think it's an issue 2.
  • guesserguesser
    edited February 2012
    Spectrum wrote: »
    hmm... but I should open the Speccy... I'm not into that!
    It's so old... I don't want to do that...

    In any case, do you think it need some fix or it will become better just letting the Spectrum warming up?

    Er, if it's had a composite mod done then it's been opened to do that already :p
    My rubbish website including the redrawn Amstrad schematics and the Sinclair Wiki.
  • SpectrumSpectrum
    edited February 2012
    guesser wrote: »
    Er, if it's had a composite mod done then it's been opened to do that already :p

    Right, right, but I WASN'T the one that opened it...
    However, the colours looks bad and, as I said, "yellowish".
    So, I think something is wrong.
  • MaccMacc
    edited February 2012
    Bite the bullet and open it up man, my bets is its an issue 2 also, there are four pots in a vertical line, dont worry about the top two too much, its the bottom two, turn them very slowly with a screwdriver and you should see a change in the screen colour, thats the way to get it right again
  • ingoingo
    edited February 2012
    Macc wrote: »
    dont worry about the top two too much, its the bottom two, turn them very slowly with a screwdriver and you should see a change in the screen colour, thats the way to get it right again
    But these resistors only control the colour difference signal. So you will control the purity of colour. This has to be done while looking at colour bars on the screen (made by a simple basic program). It is not simply adjusted because each of the trimmers control more than one colour at the same time.

    I await that the colour of the white start screen will not change because this should be neutral without colour difference signal.

    The "yellow" on white screen could be from undesired signal content in the composite signal. To improove this is possible but I doubt that it is done only by adjusting these trimmers.
    Unfortunately the video signal part of the spectrum is made very poor and the signal quality is depending on properties of the used chips and layout. It depends on the quality of ground line and the purity of the 5V and 12V power supply. So for a people without any experience in this field it will be difficiult to succeed I think.

    Regards Ingo.
  • SpectrumSpectrum
    edited February 2012
    ingo wrote: »
    But these resistors only control the colour difference signal. So you will control the purity of colour. This has to be done while looking at colour bars on the screen (made by a simple basic program). It is not simply adjusted because each of the trimmers control more than one colour at the same time.

    I await that the colour of the white start screen will not change because this should be neutral without colour difference signal.

    The "yellow" on white screen could be from undesired signal content in the composite signal. To improove this is possible but I doubt that it is done only by adjusting these trimmers.
    Unfortunately the video signal part of the spectrum is made very poor and the signal quality is depending on properties of the used chips and layout. It depends on the quality of ground line and the purity of the 5V and 12V power supply. So for a people without any experience in this field it will be difficiult to succeed I think.

    Regards Ingo.

    Damn!
    Looks like I can't do anything to improve the quality of the image.
    In any case, since I've to send the Speccy to fix (it have some memory fault) I will ask to fix this colour trouble, if possible...
    The quality of the image is quite good, but I miss the Spectrum's shiny colours (they were my pride when compared to my friend's C64...)

    =(
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