my 88 560SL has a Becker that the prevous owner replaced with a jensen, he told me the becker just stopped working one day and he was told the mother board was bad and needed replacing, but he did not want to pay to have it fixed, anyone know how to test it or know who could fix it?

You may be better off buying a replacement on ebay...

Becker of North America has a web site and for $25.00 they will give you an estimate or fix it and waive the estimate charge. See below-


http://www.beckerautosound.com/