I'm interested in buying a SEGA CD, and I was about to do so today. The guy I was buying it from offered to show it works and I agreed. In short, we couldn't get it to function, only the genesis half would come on. He didn't know what the "mixing" port was for and neither did I. It was about this time that I noticed the "access" light of the CD wasn't coming on. We tried, but couldn't get the sega cd to come on or play.
Um, help?
EDIT: The set up looks like this:
(I read the following, almost no use:
http://my.ais.net/~xtreme/SF/SCD/SCD2.html