Amplifier Problem - ***SOLVED***

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.

Reply to
EADGBE
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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

Reply to
Arfa Daily

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

Reply to
GAGI-9A6AAG

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.

Reply to
James Sweet

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...)

Reply to
GAGI-9A6AAG

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

Reply to
Arfa Daily

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 :))

Reply to
GAGI-9A6AAG

would

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

Reply to
William Sommerwerck

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.

Reply to
James Sweet

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