[tmo24]

I had the same problem on my 07 e92 with Logic7. The professional head unit had lights and controls etc but zero sound, no matter the input. I also have an 07 e90 with logic7 so I decided to swap the head units to see if it made a difference. It worked fine after the swap and the other car had the same issue so I ruled it out to be a bad head unit. I did a VIN search to see that I had the S677 hifi system. I didn't have bluetooth telephone or USB in the center console. So I actually went to ebay and found one that displayed the VIN. I ran a search on it and it also had S677 but with bluetooth telephone and the factory USB in the center. I installed it and the audio worked fine, had the logic 7 EQ, gave me bluetooth telephone (I guess I had the module but it wasn't coded?) and then installed a MOST adaptor and it worked without having to code it. Food for thought. It was like $70 shipped. It might be worth it to try to see if you can swap with a buddy who has the same head unit. Its about a 2 minute swap total including taking a drink of beer. I could be way off base with your issue but I wouldn't rule it out.

[ctuna]

It's important that the terminology be kept straight because it's already confusing
enough.

Stereo = base system = no amp
Hi Fi = 6 channel analog amp with analog inputs = 676
Top Hi Fi = Logic 7 = 9 channel amp with optical inputs = 677 and 688

[TboneS54]

So with more help from elec eng friend, we used a laptop and a cut up pair of headphones with 3.5mm jack to test both output of headunit and fed a 400hz tone to the amp (just one channel - amp/speaker worked fine). Headunit output was dead. Wiring, battery, amp, speakers all fine.

Put in another headunit, one just like mine with blutooth, usb, aux, and no coding needed - music is back!

In the end, had nothing to do with low battery, blown fuses or bad amp... go figure.

When I shake the original headunit, something is loose.