I was trying to troubleshoot a problem with my Bose Companion 3 Series which is constantly making a low-pitched buzzing noise (about 50Hz, I'd guess) through all the speaker channels, including the sub. It does this even when the 'pod' shows an orange light - so it should be off - and no other sound comes out of any of the channels. (I've tried both inputs and several cables - no hint of any signal at the output, just buzzing.)
I think it's probably a problem with the power supply board. There's a three-wire cable joining the amp board and the power supply board to each other - with red, green, and black connectors. Currently the red connector is at +12V, and the black and green are both at 0V. I'm sure one of them should be different - perhaps -12V, or possibly +15V? I'm not sure.
And yes. I'm aware that Bose stands for "buy other sound equipment", etc... etc... I can't afford to, and was given this as a broken 'present' (hah)...