So my speaker stopped working one fine day, no sound, power led is not coming on. I opened the subwoofer to see whats wrong and I saw this black hard mass on some capacitors:
When I try to scrape it off its hard an comes off as powder and it leaves a black stain on the PCB.
Is that the electrolyte from the capacitors?
How come so many of them have it all at once?
So ill have to replace them as they are dead?
Since it doesn't really resemble the glue/goop commonly used to fasten electrolytic caps to PCB's... (*and since it's not on all the similar caps), it is highly likely that this is the leaked out electrolyte. Since replacing these should be rather cheap... it's worth it to just replace them with similar (maybe even higher voltage) capacitors.
It really does look more like a leakage issue rather than glue since leakage often presents itself as a black substance.
Why so many at once? I blame AGE and ABUSE (abuse can be the same as designed too close to tolerance) though there could be a bigger issue that is causing the caps to be unhappy.
Keep in mind... this still could be sparingly but sloppily applied "glue" since the caps don't show signs of 'failure bulge'
Got a closer-up picture from the side of the base of a cap with the stuff on it?
I think it's glue; I've seen cheap audio boards with black epoxy that looks a lot like that.
Those caps have the + at the top - Often that's where it will fail from when caps fail. Though ofc, they can fail like the ones in that above picture (I've never seen that, vs about a dozen boards with caps leaking from the tops).
I suspect the problem is a semiconductor or fuse
Thanks for the quick reply,
Here are some more pics:
I removed a cap having lots of black stuff on it, stripped off its plastic cover and then scrapped the black stuff, looks like this:
It is charging and discharging like normal, so it's not the electrolyte seems like...but how could anyone put glue like that, I would do better in my sleep. And the speaker is from Creative, a reputed brand for speakers here.
The problem could also be cheap caps - not too many years back, a whole a--load of "fake" caps went on the market and into everything - motherboards, power supplies, televisions, speakers/subwoofers/amps - you name it - if it had a cap, there was a chance it was one of these knockoffs.
Most of these have since died - but there are still plenty out there as ticking "time bombs" just waiting to go. If you do some research, you can find out more about this, and the names of the "brands" of caps they were marketed under.
You can possibly fix such problems - more than one person has rescued nice big screen LCD TVs from the garbage heap, just for the cheap price (and labor) of replacing a bunch of dead caps.
Sometimes, though, you may find it is more trouble than its worth - because when the caps blew, the issue propagated and perhaps weakened or bork'd other parts in the circuit. You could get all those new caps in, plug it in, and those caps could blow (because other parts are fubar'd) or other parts could blow (or already be blown) - or everything works ok for a few days, weeks, months - then other parts blow (because they were weakened). Then you are chasing a rabbit down a hole, because those parts failing may have caused even more parts to fail, etc.
If you do replace them - replace them with same value caps, but a higher voltage rating (as noted already) - and use a known name-brand manufacturer for the caps (eg Panasonic).
Truth:
You can possibly fix such problems - more than one person has rescued nice big screen LCD TVs from the garbage heap, just for the cheap price (and labor) of replacing a bunch of dead caps.
A friend has a working Visio 50" TV for this reason.
It looks like glue, not leaked caps.
Also, a "analog" product like your speaker won't stop working like that. Leaky caps will lead to audible hum, not a dead product.
// Per.
Zapro:
It looks like glue, not leaked caps.Also, a "analog" product like your speaker won't stop working like that. Leaky caps will lead to audible hum, not a dead product.
// Per.
yes i think its glue too, found this:
http://www.jestineyong.com/about-decayed-glue/
but everything else seems to be working fine, power supply is fine, volume control is fine, speaker to subwoofer connection is good...ill replace the caps and see if that works
I've seen a lot of electronics with this white glue that turns brown and eventually black, and becomes conductive as it darkens.
Electrolytic caps are probably the most trouble-prone component. Sniff them - do they smell fishy? When they leak, it smells fishy and is usually kind of sticky.
Creative makes their stuff in Chinese factories, same as just about everyone. Assembly line workers in a hurry.
No it doesnt smell fishy, just nothing 
Though when i touched a soldering iron to the black mass, it melts and vapourizes smelling something like a petroleum derivative.
Srijal97:
No it doesnt smell fishy, just nothing
Though when i touched a soldering iron to the black mass, it melts and vapourizes smelling something like a petroleum derivative.
Again, it's just glue.
Find out what is broken, disregard the caps, because they are not to blame here.
// Per.
I think I'd still scrape the black stuff off. If they don't seem to be bulging or leaking, and the ESR seems OK, probably not the caps. Small capacitors, rather than obviously leaking or bulging, may have the rubber seal on the bottom become hardened. This indicates a dried out capacitor that has gotten hot and cooked the rubber.
Do you have an ESR meter?
No, i dont have an ESR meter.
But I removed all the caps, discharged them, measured voltage with dmm, charged with 9v battery, measured voltage, discharged...
All of them charged and discharged properly.
So then I scraped the black glue(it connected two jumpers together), it still leaves a black stain on the pcb. Now since the caps are cheap ill also put new ones back in and see what happens. Will let know if that works.
That won't tell you ESR. How about the value of capacitance? A capacitor may still hold a charge but have greatly reduced capacitance.
Srijal97:
So my speaker stopped working one fine day, no sound, power led is not coming on.
Fuse? Nothing in that description screams capacitor to me.
Good point, we all got wrapped up in the capacitors.
Check if there is power supply voltage.
Yes power supply is fine, I measure 12-13V AC at the transformer ends(transformer is rated 10V but im getting more than that, is that the problem?), ~16V Dc at the filter capacitor and 13-14V at the speaker atached to the subwoofer, this speaker has the volume controls and power LED, and gets sound input.
Thsi speaker is connected to the subwoofer with a 9 pin Din connector, though only 6 pins are used.
Now after replacing caps and cleaning black glue I see that the power LED is turned on but not at full brightness, its dim and not very noticable. But still no sound output. The speaker itself(inside the speaker case) is fine, attached a sound generating circuit to that to test. Also the sound Input plug is fine. I dont understand where the problem is..
Ill post pictures of the other speaker circuit board and more later, cant do it now..
Also this topic isnt related to arduino, so should I ask this again in some other forum like tomshardware and continue there?
Well, it is General Electronics.
The output amp may be shorted. It seems strange that you'd get a drop of 2 to 3V between the filter cap and the amplifier. Or that the LED would be dim.
Trace out the wiring, look for burnt spots on the PCB traces.
the right speaker shows 13V input when its off and 2.2V when its on. The raw audio signal reaches the speaker, goes through volume potentiometer and to the subwoofer where it should be amplified. But the amplified audio signal isnt produced and doesnt reach the speaker. Thats the problem.
There are two ICs having heatsinks on top of it, this seems to be the amplifying IC. So theres some problem in amplification, maybe the IC or some other component is responsible.
I think ill take this speaker to some service guy who knows better