OK. I do not know the exact number for the diode off hand, because I don't have the same radio in front of me. On most cb radios, this diode is usually located on the component side of the pc board, close to where the positive lead solders to the board. Most of the time when it burns, it just becomes brittle.
If you do replace it on your own. The diode is called a rectifier diode, which you can pick up at radio shack or at partsexpress.com. The part number is between 1N4001 to 1N4008. When installing be sure to observe polarity, making sure that the side with the silver band is facing the direction of the arrow.
If I can help anymore, please don't hesitate to ask.