Debugging S-Video problems

There are some specific tips for debugging S-Video connections on two separate Co-ax cables (one for luminance (Y) and one for chrominance (C)). Here they are…

S-Video uses separate connections for the luminance and chrominance signals, but now instead of just debugging one connection path you have to debug two. Here are some pointers.

1. the video sync pulses, used to indicate the start and end of each line and field of video are added to the luminance (Y) signal, so if you are not getting stable images at all, it is likely that the Y connection is broken somewhere. Typically you might get a rolling image that is recognisable but is never stable.

2. If you ARE getting a stable image, but it is monochrome, then there is likely to be a problem with the C connection.

3. The most common problem with Y/C connections using dual Co-ax cables is swapping the cables somewhere – i.e. connecting the Y to the C and the C to the Y.

4. Some projectors double up the composite and the Y connections on the same BNC and then have another BNC for the C. In my experience you HAVE to enable Y/C operation, otherwise you will only ever get monochrome images.

So to summarise the symptoms match the problems as follows:

Y connection broken – no stable picture (rolling image) or no picture at all C connection broken – stable picture but mono only Y and C connection broken – no image at all Y and C swapped – no stable picture or no picture at all

So, if in doubt you should always try to sort the Y first, to get a stable picture first, then sort the C to get colour.


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