Hello,
I have come across various SCART cables which cause this.
I have one SCART cable which displays the graphics OK but there is no sound, and I have another SCART cable which plays sound but doesn't display graphics. Tested on an Amiga CD32/SX1 combo.
You may need to buy a SCART cable from an Amiga dealer (UK AmigaKit) which are guarenteed to work with Amigas.
Kind Regards, Michael
aka rockape