Hello Murali,
So S-video input works and CVBS doesn't.
A few questions:
1) Is it PAL or NTSC input?
2) What is the source? - Video generator, DVD, etc...
It could be that the settings that you are using to configure the ADV7403 in CVBS mode may be in error - will take a look at your attachment to see if anything sticks out.
regds,
Denis