fisher@star.dec.com (Burns Fisher ZKO1-1/D42 DTN 381-1466) (01/12/87)
Followup: I followed the instructions of several respondants and got a chroma signal from the junction of R68 and R67 and took it to pin 5 through 200 ohms. I ran the existing lumma signal to the lumma input of my Commodore 1702 monitor and the new chroma signal to the chroma input. Yes, it does work fine. However, I have to say I can't tell the difference between using the new chroma signal composite video into the chroma input. Both seem equally good. I guess I can see now why Atari did not bother with the separate chroma when the designed the XL. Notice that I am talking about running composite to chroma input. If I run composite into the composite input, the picture quality is distinctly inferior. Just curious...has anyone else (perhaps someone with an 800 non-XL) tried substituting composite for chroma? Can you see the difference? Thanks for all your help. Burns fisher%star@DEC.COM
jhs@MITRE-BEDFORD.ARPA (01/12/87)
Looking at the schematic to the 800XL, it appears that the composite video output does not include any filtering to limit the bandwidth of the chroma signal before combining it with the luminance, as is normally done in television broadcasting. This would explain why the composite signal can be used as an input to the Commodore monitor's chroma input without loss of resolution. I am surprised that there is no visible difference, however, because I would think that the luminance signal might cause interference with chroma circuit operation. -John Sangster / jhs@mitre-bedford.arpa