"EADGBE" wrote in message
...
Good News!

This headphone amplifier has been REPAIRED and is now working
perfectly.

Here's what happened:

I have been taking parallel measurements between the "good" and "bad"
channels since the beginning.

I took voltage measurements, resistance measurements, tested ALL
capacitors, and tested ALL transistors.

But someone in my original thread (I can't remember who offhand --
sorry) did mention checking the circuit board traces.

"No need," I thought. "The circuit board and all solder joints look
fine to me."

But in a fit of desperation, I nonetheless decided to whip out a
tester I hadn't used yet: my magnifying glass.

That's when I found it -- a *microscopic* crack in the trace between
the emitter of Q208 and its adjoining 3.3 ohm resistor. The crack was
so incredibly tiny that I easily overlooked it--repeatedly.

I took one of my jumper leads and clipped one end of it to Q208's
emitter and the other end of it to the 3.3 ohm resistor.

I then took voltage measurements. EVERYTHING WAS NOW ON SPEC:

Q205's collector now measures +7.09V, and Q206 now has the following
measurements:
B: +6.51V
C: +7.08V
E: +5.84V

I was able to bridge the crack with a well-placed solder trail, and
the headphone amp now sounds great.

A BIG "THANK YOU" TO EVERYONE WHO HELPED ME OUT! I OWE YOU BIG TIME.

Well done on finding the problem - a deserved result. However, can I make
one suggestion ? Don't rely on just solder to bridge the crack, as it *will*
cause trouble again. The crack causes the solder to form a crystalline
'wall' above it, inside the joint, as it resolidifies. Any cracks, however
tiny, *must* be bridged by at least one strand from some hookup wire. If you
can get a good joint to a solder point either side of the crack, then do
that. If that is not practical, scrape back the solder resist on the
tracking either side of the crack, and then bury your strand of wire in the
solder bridge. As I know that you do these repairs to further your
knowledge, that is a professional 'reliable repair' tip that you should add
to your knowledge base.

Arfa