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Tech Head - The Technology Section
The Work Bench and Soldering Station
TV colour comes and goes...
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<blockquote data-quote="spiney" data-source="post: 171986" data-attributes="member: 192438"><p>just to expand on what Llew said ......</p><p></p><p>The complete colour image is formed from 3 separate pictures combined (red green and blue). But, these can be "derived" in different ways.</p><p></p><p>1) The SCART lead - with its many wires! - carries these 3 pictures separately on 3 different wires, in either RGB (straightforward) or YUV (matrixed) modes. You may be able to select which mode, on both tv set and/or SCART connected devices. Which one is used doesn't really matter, it's still really 3 different pictures, and should always give you colour, from any device connected to TV set via SCART.</p><p></p><p>2) Off air, on analogue transmissions, the tv has to "lock onto" the colour subcarrier (PAL system, in Turkey?), to re-derive the colour signals from transmitted luminance (Y) and chrominance (UV). If it can't "find" the subcarrier, then you'll just get Y, which is the monochrome picture!</p><p></p><p>It's easy to get Y, over quite a broad tuning range! Getting UV is harder, your tv has to be more precisely tuned. Also, as components age, the "default" frequency of your set's PAL oscillator can drift, and may need re-adjusting to get any "colour lock" at all, almost certainly that's what the repairer did.</p><p></p><p>(As components age, it may still be possible to get off-air colour by very carefully re-tuning, until eventually this won't work at all!).</p><p></p><p>3) But, this "subcarrier" version of the colour signal is also on the SCART lead, as a single signal on just one wire. If that mode is selected, then a TV which has problems getting the broadcast subcarrier may also have problems "locking onto" the SCART version, even though the SCART one doesn't involve any tuning!</p><p></p><p>4) You may still be using the video recorder subcarrier mode output, either in UHF (aerial) or SCART (CVBS) form, rather than one of the 3 wire SCART modes. See if you can change this on setup menus. Or, try carefully re-tuning whichever TV channel you're using for the video recorder output.</p></blockquote><p></p>
[QUOTE="spiney, post: 171986, member: 192438"] just to expand on what Llew said ...... The complete colour image is formed from 3 separate pictures combined (red green and blue). But, these can be "derived" in different ways. 1) The SCART lead - with its many wires! - carries these 3 pictures separately on 3 different wires, in either RGB (straightforward) or YUV (matrixed) modes. You may be able to select which mode, on both tv set and/or SCART connected devices. Which one is used doesn't really matter, it's still really 3 different pictures, and should always give you colour, from any device connected to TV set via SCART. 2) Off air, on analogue transmissions, the tv has to "lock onto" the colour subcarrier (PAL system, in Turkey?), to re-derive the colour signals from transmitted luminance (Y) and chrominance (UV). If it can't "find" the subcarrier, then you'll just get Y, which is the monochrome picture! It's easy to get Y, over quite a broad tuning range! Getting UV is harder, your tv has to be more precisely tuned. Also, as components age, the "default" frequency of your set's PAL oscillator can drift, and may need re-adjusting to get any "colour lock" at all, almost certainly that's what the repairer did. (As components age, it may still be possible to get off-air colour by very carefully re-tuning, until eventually this won't work at all!). 3) But, this "subcarrier" version of the colour signal is also on the SCART lead, as a single signal on just one wire. If that mode is selected, then a TV which has problems getting the broadcast subcarrier may also have problems "locking onto" the SCART version, even though the SCART one doesn't involve any tuning! 4) You may still be using the video recorder subcarrier mode output, either in UHF (aerial) or SCART (CVBS) form, rather than one of the 3 wire SCART modes. See if you can change this on setup menus. Or, try carefully re-tuning whichever TV channel you're using for the video recorder output. [/QUOTE]
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The Work Bench and Soldering Station
TV colour comes and goes...
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