It seems Amigakit offers services for repair. They also have service for floppy, and I noticed it was mighty dirty to so 71 eur for replacing capacitors and cleaning up the floppy seems okay.
They also have "A4000 / A1200 / A600 Audio Repair"
I have not heard of any common issues with audio for 1200, or am I mistaking?
I'd recommend you agree a timescale for the repair with Amigakit before sending them your hardware, just to make sure there is no unexpected delay.
If you need the job done quickly and Amigakit are busy with other work, you could try Cosmos, he offers the same service for replacing the caps and reckons he can turn the job around the same day he receives the board.
