I had a problem with my 83 CC. I found this guy on the net

http://gdl-online.com/mbz01.html

He happens to be about 10 minutes from my house wich was crazy b/c I live in San Luis Obispo, CA (1/2 way between LA and SF) ... any way, the web site has some great diagnostic test to perform yourself and if your amp is bad he'll fix it and send it back ...