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.

"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

"EADGBE" wrote in message

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


good4u )

i was folow developing of case you got....i am hobbist to and from my
experience i can tell that malfunctions caused by "cold solder" are most
dificult problems to solve...especiali when there is some random states of
working and it doesnt working...and again...and again...but you cant see it
where does it happening...

even tracking signals is sometimes waste of time...even method of searching
cold solder in dark room (so you can see the sparking place)...seems
sometimes is pure luck that matters! )

Greethings from Croatia...
Gagi

i was folow developing of case you got....i am hobbist to and from my
experience i can tell that malfunctions caused by "cold solder" are most
dificult problems to solve...especiali when there is some random states of
working and it doesnt working...and again...and again...but you cant see
it where does it happening...



They're one of the most common faults as well, many times more extensive
failures start out as cold solder joints. Often prodding or flexing the
board will make them more obvious.

"James Sweet" wrote in message

They're one of the most common faults as well, many times more extensive
failures start out as cold solder joints. Often prodding or flexing the
board will make them more obvious.


indeed....first and nice example are PC monitors....their PCB is mostly
always in malfunction cause of some cold solder (except when is about HV,
horizontal transistor..etc...)

"GAGI-9A6AAG" wrote in message
...

"EADGBE" wrote in message

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


good4u )

i was folow developing of case you got....i am hobbist to and from my
experience i can tell that malfunctions caused by "cold solder" are most
dificult problems to solve...especiali when there is some random states of
working and it doesnt working...and again...and again...but you cant see
it where does it happening...

even tracking signals is sometimes waste of time...even method of
searching cold solder in dark room (so you can see the sparking
place)...seems sometimes is pure luck that matters! )

Greethings from Croatia...
Gagi



Interestingly, for the most part, I used to find the locating of bad joints,
one of the *easiest* things to do in fault-finding. As well as having sharp
eyes to spot obvious ones, use of the right techniques i.e. prodding,
flexing, heat, cold, and above all, having a good idea exactly *where* to
look, and at what *type* of component, would quickly reveal the source of
the problem.

Sadly, that has now gone 'out of the window' with modern soldering
materials. I have found many bad joints made in lead-free, that have shown
no external physical signs of being bad, such as cracked around, and have
gone good and bad completely at random, failing to respond to any of the
'normal' techniques for finding them. Add to this that my eyes are not as
good as they were 20 years ago (even 5 years ago...) and that *all*
lead-free joints *look* bad with their dull crystalline surface, and I would
have to agree that now, bad joints are likely to turn a job from a
one-coffee money spinner, to a pot-of-coffee frustrating money loser ...
:-(

Arfa

"Arfa Daily" wrote in message

Interestingly, for the most part, I used to find the locating of bad
joints, one of the *easiest* things to do in fault-finding. As well as
having sharp eyes to spot obvious ones, use of the right techniques i.e.
prodding, flexing, heat, cold, and above all, having a good idea exactly
*where* to look,


hehe, sure, when; as you said also; cold solder is obvious...
but when it isnt..then?!...its supposed that you know theory very well so
you can persume what it could be...

like; if RGB is losing red color; sure you wont look horizontal-transistor
then you will first look the cable or connector inside )


however; i agree that prodding and flexing PCB is most accurate technique of
finding cold solder....i use a wood stick or back of screw driver for
that...

for nosie sparks but not visible ones i am using "home made" and primitive
stetoscope....i put in ear one side of gum pipe and with other side i am
"scanning" for noise it bothers me...hehe, moving around electronic
components like trough mine field )

Add to this that my eyes are not as
good as they were 20 years ago (even 5 years ago...) and that *all*
lead-free joints *look* bad with their dull crystalline surface, and I
would
have to agree that now, bad joints are likely to turn a job from a
one-coffee money spinner, to a pot-of-coffee frustrating money loser ...

What would happen if service technicians got together and agreed to refuse
to service equipment made with lead-free solder?

"William Sommerwerck" wrote in message
. ..
Add to this that my eyes are not as
good as they were 20 years ago (even 5 years ago...) and that *all*
lead-free joints *look* bad with their dull crystalline surface, and I
would
have to agree that now, bad joints are likely to turn a job from a
one-coffee money spinner, to a pot-of-coffee frustrating money loser ...

What would happen if service technicians got together and agreed to refuse
to service equipment made with lead-free solder?


I think we'd all go tits-up William ... !!

Arfa

William Sommerwerck wrote:

Add to this that my eyes are not as
good as they were 20 years ago (even 5 years ago...) and that *all*
lead-free joints *look* bad with their dull crystalline surface, and I
would
have to agree that now, bad joints are likely to turn a job from a
one-coffee money spinner, to a pot-of-coffee frustrating money loser ...

What would happen if service technicians got together and agreed to refuse
to service equipment made with lead-free solder?


That is exactly what they want them to do.


--
http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm

"William Sommerwerck" wrote in message
. ..
Add to this that my eyes are not as
good as they were 20 years ago (even 5 years ago...) and that *all*
lead-free joints *look* bad with their dull crystalline surface, and I
would
have to agree that now, bad joints are likely to turn a job from a
one-coffee money spinner, to a pot-of-coffee frustrating money loser ...

What would happen if service technicians got together and agreed to refuse
to service equipment made with lead-free solder?



They'd go out of business.

Pretty much everything made now is lead free, refuse to service it, and it
simply encourages people to do what they're already doing in droves, throw
it out and buy a new one.