RE: radio or speaker problem

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> it looks like the final stage(s) of the power amplifier(s) are
> self-exciting.
> This is usually caused by a parasitic positive feedback due to a lost
> ground. My
> guess you have a burnt ground trace somewhere. Open it up and look at the
> PCB.
> In most cases it is easy to spot.
> 
... actually I would suspect an electrolytic capacitor that has dried out
and changed value.  This sort of thing used to be very common back in the
old vacuum tube days, as the heat generated would tend to dry up the
electrolye over time ... don't see it too much any more.  As someone else
pointed out this capacitor might be one of the main filter caps, but I'm
thinking that it is more likely a bypass or coupling cap in a power amp.  

I am learning a bit more about the Bose system for the V8q ... it appears to
me that the system uses a stock blue-dot ;) radio, with Bose doing its
"magic" at the speakers.  Can you tell if it is only one speaker unit that
is causing the noise, or is it common to all channels?  If it is common it
is likely to be in the head unit.  You might be able to unplug the speaker
units individually to see if you can make the problem go away.  

Good luck!
Steve Buchholz
San Jose, CA (USA)