I recently bought an Atari 2600 over the Ebay Auction and was thrilled! I received it and the computer switch worked but marginally .... meaning it would switch from tv to game and back but the picture quality was VERY POOR.
So I did what you said. I went to Radio Shack. I bought 2 items at a total cost of $9.48 plus tax and have fixed my problem! Now I can enjoy playing the games and the picture quality is wonderful.
The items needed were Radio Shack item #278-276 which is a Phono-to-F Adapter as well as Radio Shack item #15-1232 which is a Mini A/B Switch.
So, I wanted to put this information out there in case anyone else is experiencing a similar problem .... now it's solved. Thanks so much! Joyce