Hello Alan
> Many might disagree with me her and I would like to say be very careful
> while working this way but I often find that if no oscilloscope is
> available that simply testing the signal path with a wire attached to
> the tip of an audio jack will tell you allot.
I do this all the time, the way you are describing (and I think most
technicians do it that way). Use only extremely simple speakers or
headphones for this, because there may signal transitions happen, which
can kill tweeters or delicate headphones! I have a set of old car hifi
speakers on my workbench for this.
Florian