I seem to remember seeing the "E2" error code on my radio when it went bad. It turned out to be the actual tuner which is in the trunk (the head unit in the dash is basically buttons and the tape player).
There is a separate Becker forum. Might want to check this out. Do an internet search on "becker board" and you should find it.
The other excellent source of info is Beckerautosound. They have a web site and very knowledgable techs. One of them, Ed Ebel, is a regular on the Ritter/Easley list.