Hi!, On 2017-08-31 20:06, Mia Magnusson wrote: > Hi! > > As many people already know, C64 is older than the consumer S-video > signal format, and doesen't comply completely to that standard. > ... I don't know all the answers, but I might add something (or what)... - In a TV set / composite monitor, group delay between luma and demodulated U' and V' components is inevitable, due to the need of separating two signals of different bandwidth first (chroma from luma), and then the need of demodulating the color difference signals (whilst luma, by itself, doesn't need to be demodulated). To compensate for that, the devices usually have a small, some-10 ns analog delay line in the luma signal path. How well this compensation works depends on analog components and setup in earlier PAL TV sets and monitors. (Later models might have that integrated into some chip, just as the earlier 1H glass electroacoustic delay line has made it to a form of sampled mixed-signal integrated circuits later, and suffer less from the degradation and/or variance of analog component values). - I've never noticed this unusual color delay problem on C64s on late (high resolution, small pixels mask) CRT tvs and monitors myself. (On the other hand, it was long ago when I played around with a C64 the last time). Nor did I ever notice such delay with 264 series machines. I definitely did notice the problems that originate from the unusually high pixel clock and luma bandwidth of the C64 (--> pseudo-colors and color artifacts as a result), but that one might be unrelated to the color shift problem you're describing. - Some years ago, I had a long (and still not finished :-) ) fight fixing and correcting a PAL Commodore 1702 monitor (a 1702-T / a Toshiba CRT version, to be precise). All I can say that the luma delay was anything but perfect after that many years, or by design, or I don't really know how-why. The delay even differed for composite and separate luma-chroma input mode; nevertheless it was way off for both modes (about 1...1.5 pixels difference on the screen), both with Commodore machines, a recent DVD player that I used to generate test signals, or a standard TV picture generator instrument that I purchased and used later. I've never noticed that problem on my other "old style" (composite / separate luma-chroma / large raster mask) Commodore color monitor (a 1801, that is). All in all: I'd say, if the question was some strange luma-chroma delay value of some particular Commodore display make, I'd much rather suspect a by-design poor luma delay circuit than some third-party supplier purposely tailoring the luma delay value of their product to the task. (As a side-note, AFAIK basically all Commodore monitors have been manufactured by contractors... JVC, Sharp, Philips, Samsung, and so on; and also, the picture of the C64 would need to be consistently differently shifted on standard CRT TVs and early Commodore displays if Commodore had had the manufacturers tailor the luma delay value of their products; which AFAIK has not been confirmed). - For the 1702 fix, I think I found something promising: some manufacturers offer tapped analog delay lines (that is, usual, coil-type delay lines with many taps). With that I think I can replace the original delay line in the display, and select a tap that provides optimal delay. I'll definitely calibrate the thing against some standard signal source, and not a Commodore machine (but as said, ATM I don't expect significant differences). Such delay line might also be a suitable base component for your case (or, I don't know... with that, impedance matching might become difficult). Best regards, Levente Message was sent through the cbm-hackers mailing listReceived on 2017-08-31 22:00:07
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