[SOLVED] 2way active speaker sounds distorted

[5inc]

I have this "AVL" active speaker. No info on the net whatsoever, can't even find to buy one alike.
Anyways, it has this issue, it sounds VERY distorted, even at low volume, and it affects both low and high drivers. I have to say this had happened before and it fixed itself up one day, and a week later it was bad again.
I took it appart several times, checked drivers, and basic electronic components, tested all diodes, no bulged caps or phisically burnt resistors.

Any ideas where to look?
Thanks

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a friend told me to try changing the bridge rectifier but nothing, it does the same on a new one

 

[Audioguru]

Cheap no-name-brand audio products (and all other products) work poorly.

 

[LISA_DALTON]

Audio guru gave a poor opinion, no help.
Your friend doesn't know what he was talking about, randomly changing parts never works. Bridge rectifiers are not high fail items, or subject to being intermittent. If it was a intermittent bridge rectifier, it would put out a 60 hz loud hum.

A problem like this needs to be troubleshot while it is failing.
Do you have access to a oscilloscope? Without it, it will be tough.
Is this a single speaker?
Or does it have a left and right input. More info, like a picture would be helpful.
But from the sounds of it, if there is one part to randomly replace, it would be the integrated amplifier assuming it has one.

Hitting the amp with freeze spray when it fails would be what I tried first, If it immediately fixes the problems then fails on warm up again, you have found your problem. Leave it apart enough while it is running, to be able to do this test.
Lisa Dalton

 

[Audioguru]

Audio guru gave a poor opinion, no help.

Sinc bought a no-name-brand active speaker with no info and cannot even find another one. Why do people buy junk like that?
"Always it has this issue, it sounds VERY distorted, even at low volume, and it affects both low and high drivers." But its problem seems to be intermittent.

I recently bought an active speaker system with subwoofer on sale for a low price. It is name-brand with lots of info and is available everywhere. It became intermittent and its pcb looked fine. I resoldered all joints on its pcb that fixed it.

 

[5inc]

Audioguru, you are right. It is a cheap piece of garbage and it works poorly, but when it did work it was just what i wanted, a light, low power amplifier and speaker all in one. I don't expect miracles on this thing, but it did work once, and i want to repair it mostly to learn, as I do with every other broken gadget i get my hands on. It's more for the path than for the ending.
Also I never spent a cent on it, a friend gave it to me and bought a proper one for himself when he found this issue.

I'm a rookie on this field, also I don't know anyone who is an electronic expert to guide me, so to learn i must ask, and some times the answer I get given is not correct or relative to the case. That's why I came to this forum on the first place. I apologize if my posts aren't as concrete or detailed as they should.

Again, I am new to forums in general, and by far not an expert on the matter, just a kid (not so kid any more) with some time to learn, a near-0 budget and a few electronic gadgets that won't work for stupid reasons.

That said, I don't have an osciloscope just yet, I'm planning on getting one of those hantek usb ones when I can afford it.

Back to business, Lisa, It has one low end speaker and a tweeter. On the line input, it has a double RCA connector and one XLR, and another xlr input for mic. It also has an xlr line output.
4 pots for line gain, mic gain, bass, treble. Will try n get a camera to send a few pics

I used freeze spray on the IC, (and everywhere in the board) while it was sounding, with no results. I had also re-soldered all joints on the boards a month ago. nothing. I'm out of ideas.


And, Audioguru, I said anyways, not always. The problem IS intermitent (I never denied it), since it has worked for some time, then gone bad, then good, and bad again. It didn't fix itself up again so I gathered it was up to me if i want to get it to work again.

 

[schmitt trigger]

At minimum you require three pieces of test equipment:

A low distortion sinewave generator (some people have used a computer sound card for the purpose)

And most importantly, an oscilloscope.

You will have to trace the audio signal from beginning to end. Without a schematic it will be a pain in the neck but it can be done. At certain stage the signal will become distorted. This is where you start troubleshooting with a DMM.

 

[LISA_DALTON]

Guru,
who cares if YOU think it is junk? It works for him. That is what matters.
And almost everything can be repaired.

5inc,
Does it use an integrated amplifier? You know, a power IC for an amp? If so, 1 or 2? (left and right or 1 mono)
If freeze spray did not fix it, (temporally of course), and re-soldering, I would risk replacing the amp if logic dictates.
(i still don't know if it is stereo or not), and if it uses 1 IC amp for L&R if it is. If it is stereo, and it uses 1 IC amp, replace the amp, if both sides are affected. I hate the shotgun method, but this is a very good risk in this case.

The 1st thing to look at when t-shooting anything electronic is the power supply, and if your meter says it is holding a steady logical voltage, it is back to the IC amp. Check the # on the amp and look it up (google it), you will be able at least to know what voltage is supposed to be and at what pins.

That should keep you busy for a while, and rots of ruck.
-Lisa

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I do NOT disagree with Herr Schmitt above, but a DC meter will get you by JUST for my suggestions above, even if it is analog.
Sometimes analog meters tell you more than digital ones, as analogs can show you changes in voltage/resistance that digitals cannot react to fast enough. Think of it as the cheapest "scope" you could possibly get. ; )

 

[5inc]

Hey people,
As I said earlier, can't get my hands on an osciloscope just yet, but I do know someone who told me he has the same hantek usb one I was thinking on buying, so when he can meet we'll get our hands on it. On the meantime, I'll do what I can with the DMM.

Schmitt, could an in-built pc sound card perform as a sinewave generator for beginner purposes? I also have a native instruments sound card wirth rca outputs if that wasn't enought to begin.

Lisa, the integrated circuit we are talking about is a 15pin TDA7296, the datasheet says it's a monolithic IC so that's mono right?

I checked diode/continuity from the heatsink through all pins(from the back side of the board) and got continuity on pins 5, 8, and 15. So I **** up all the solder, and reallize pin15(-Vs(power)) was barely inside the hole. Maybe it didn't even make contact. Since it was allready half clean I tried to take it out gently, but ended up making a mess. but i got it out, and test out of circuit beeped only on pin 8 (-Vs(signal)). I re-checked the board and efectively there is continuity between 15 and 8, witch is clearly bridged to pin 5(N.C). I repeat, on the board, not the IC.

So 15 and 8 are both negatives, that could explain why they have continuity, also why it beeped in circuit on the 3. The only thing left to check would be to re-install it making sure all pins propperly fit through and give a last shot, if not will try ordering a replacement and pray.

Gonna do that now, will re post when it's done. :blah:

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ok, the problem was that pin 15, witch was barely inside it's hole. I had been looking at that board for so long on the wrong side :bang:

As soon as I soldered the amp chip back together, tested it a few seconds before I put it back on it's heatsink mount, and it worked! and even the sound isn't as bad as I remembered! :-D

So thanks for your feedback and ideas, god knows how long it would have taken me to find it.

Cheers

 

[LISA_DALTON]

5inc,
Glad you found the problem. Congratulations on your tenacity! You didn't even need to order a part!
Production problems are the hardest to find, because you have to start with the assumption that it was at least built right.

By the way, I looked at the Spec sheet for the IC, Monolithic means that the IC is all on one piece of silicon. Not that it is Mono audio.
But in this case, It is indeed a one channel IC anyway.

Congrats again, feels good to beat the machine, doesn't it?
Keep it up, You'll only get better.
-Lisa

 

[5inc]

Thanks Lisa,
Yes, it was hard to figure it out, the solder joint on the other end looked like it was ok, it was shiny and popping out, and when I added new solder to all joints, i didn't reallize there was a hole there since I didn't **** out the excess before.

When you do reballings, do you **** out some solder before you apply new one?

I tested the speaker on different plugs at different parts of an un-earthed house, in some I get a loud humming, in some others i don't, even with nothing plugged in the input. Do you know if there is any way I could get rid of it?

I can work my way around it, like, I don't know, maybe installing an earth wire to the setup (duh) :drevil: :laugh:, but just out of curiosity, is there some way to get that earth hum gone through some circuit of any sort?

 

[LISA_DALTON]

Hi 5inc,

"When you do reballings, do you **** out some solder before you apply new one?"
On most Reballings, you can't **** the solder out the other side. "****" is not a dirty word, it's what life often does.
Even when you can **** out the solder, you could never reapply the solder through the back of the board, and have it connect to the 1 tiny spot on the top.
If you tried pushing solder through the bottom, it would short to other spots around the 1 you wanted to connect to. Unless there is something I am missing in your question.
But in my experience I have repaired many BGA IC connections by just re-flowing the BGA IC without doing anything else. Don't move the IC! Keep the board level.
watch this! https://www.youtube.com/watch?v=MEvfBS6Tams No special tools required!
If that doesn't work, then you have to remove, re-ball, and re-flow the whole thing. And that SUCKS! :x
Get the stencils that allow you to easily place-accurately-the new spheres.

As far as far as the un-grounded house hum problem goes, WOW is your house wiring screwed up! I've
done some house wiring, and the way it is set-up, the neutral wire is supposed to be the same resistance to GND as the green ground wire. They both both connect to the exact same buss bar in the breaker box.
So there is really only 1 wire in any properly wired house that you should not be able to lick while standing in a puddle.:laugh:

The fact that you are getting a hum from some outlets, most probably means, (as you seem to already know) that there are some unsafe outlets in your house.
Make sure the owner has insurance. You are prime for an electrical house fire.

I would not make a work around for something like that, I'd go down to the breaker box and connect the GND/Nuetral wires to a cold water pipe, the one thing in your house you know is a true earth ground. It MUST be the COLD water pipe. The water heater separates the hot pipes from true ground.

Consider that hum a blessing in disguise, as a warning against a dangerous situation. And If you decide to open the breaker box, BE CAREFUL! Wear rubber gloves.
Remember there is 240V in there, and for all intents and purposes is to be considered a a infinite current source!

If you are renting, have the landlord pay for an electrician.

Happy new year!
-Lisa

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I can't believe they are censoring the shorter version of Sucks! That Sucks, and is silly. Here I thought it was you censoring yourself.