Home Stereo Subwoofer, burnt component.

Thread Starter

Hawkeyez

Joined Jul 31, 2022
7
REEL ACOUSTICS RSW-12. Started making a fast knocking noise out of the blue, unplugged rca cable, no change, had to unplug it from outlet. Plugged into another outlet in garage, no sound, took it apart one ground looked loose from the power supply so I tightened it, looked at the board couldn’t see anything, plugged it in, same noise. Took it back apart looked more closely and found this burnt.

The blade connectors go to the speaker, just below the resistors is what you’re looking at. It looked burnt but hard to tell, so while it was unplugged I took a very small screwdriver and touched it and it just crumbled, I scratched at it a little bit to see if there was still anything between but nothing, it’s all gone.

What I’m wondering is what is it? Could it be the cause of the repeated knocking sound and how am I supposed to know what to try replacing it with when there’s nothing left of it and I can’t find a schematic anywhere online? Any thoughts, suggestions or help appreciated.
 

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Irving

Joined Jan 30, 2016
3,132
Can you lift the burnt bits away and carefully clean the PCB underneath with some IPA or window cleaner on a cotton bud to see what it says - that may give a clue!
 

Thread Starter

Hawkeyez

Joined Jul 31, 2022
7
I peeled it up, it’s really hard to tell but all I can see on the board is it says C24. I can only see the C and the 4, the 2 I’m guessing. Haha
 
Last edited:

AlbertHall

Joined Jun 4, 2014
12,157
Both the electrolytic capacitors appear to have bulging tops and to have leaked - the little one at to top and the big one at the bottom.
 

Thread Starter

Hawkeyez

Joined Jul 31, 2022
7
The black cylindrical capacitors? I looked closer this afternoon and yes, there’s two big ones above the blade terminals that could be replaced and then in this picture I noticed the one just below the yellow wire looks like it’s bulging. Maybe I’ll take the board into the local electronics store and see if they can match up the capacitors and give some advice on what that other component was, maybe it’s a bead ceramic capacitor. I really don’t know much about this stuff, but I think if I can find the components I can solder them in. I only paid $50 for the subwoofer ten years ago so if I try and it doesn’t work, whatever. Would be cool to get it working again though. Thanks.
 

Irving

Joined Jan 30, 2016
3,132
Hard to tell what C24 was - it could have been ceramic but those don't tend to burn like that. Possibly it was a tantalum bead electrolytic? It clearly was in series between the ends of the two big 2W or 5W resistors and they in turn are across a speaker terminal. At 250W+ there's plenty of energy to vaporise something that's gone leaky, or it could be symptomatic of another, as yet not identified, fault, such as a failed output transistor putting a large DC offset across the speaker which could have been the reason for the failure. The sound you heard was indeed the sound of a component under severe stress - it was likely that capacitor shorting out.

Doing a quick search it seems major electrolytic replacement was commonly needed on these units as cheap 'chinese' electrolytics leaked or gassed almost from day 1. There's a number of YouTube videos on repairing RSW12, but nothing directly relevant to this issue.

Without a schematic and further investigation I'd say this is likely to be "beyond economic repair".
 

Thread Starter

Hawkeyez

Joined Jul 31, 2022
7
Thanks, I think I’ll still bring the board to the electronics store and have them match up the capacitors and find me something to replace the burnt thing, even if it’s just a guess. Unless the cost is more than $30. A new sub is going to be like $500 so I probably won’t even bother if I can’t fix this one.
 

Irving

Joined Jan 30, 2016
3,132
Thanks, I think I’ll still bring the board to the electronics store and have them match up the capacitors and find me something to replace the burnt thing, even if it’s just a guess. Unless the cost is more than $30. A new sub is going to be like $500 so I probably won’t even bother if I can’t fix this one.
Replacing C24 isn't really critical, it should work without it though the freq response/noise level might be less than ideal. But for C24 to burn like that suggests some other fundamental failure, nothing to do with leaky caps - that needs to be resolved first as its clear its not working and C24 isn't the cause, its a symptom. In one of the vids on Youtube the guy replaced all the caps, around 30-odd; that's definitely >> $30 (the big HV, low-ESR ones will be several $$ on their own) and would be a pointless expense and effort if the other issues aren't resolved first.
 

Thread Starter

Hawkeyez

Joined Jul 31, 2022
7
Ok so here’s one thing I did that may have caused that? Maybe you can confirm? After plugging it in and it made the sound again, I unplugged it, pulled a speaker wire off and plugged it backed in to see if it would still make the sound, it didn’t. So I unplugged it. Now I’m wondering if I could have caused that thing to burn up. I didn’t see a flash or smell smoke.

the reason I ask is awhile ago, it started having a faint humming sound. I just quit using it. I moved, plugged it in and didn’t hear the noise but the house is a bit “louder” with furnace and fans and fish tank. My stereo has tower speakers with 2x12” woofers so hen I have used the stereo it’s usually kind of difficult to tell if the sub is on, unless it’s a movie with some seriously low bass. It was just the other day it started knocking and getting louder and louder.

Anyway I appreciate the help, I wasnt thinking when pulling one speaker wire off that it could do damage or not. Still don’t know.
 

Irving

Joined Jan 30, 2016
3,132
Running a class D (i guess this is since its 'digital') amp with no load could generate some high voltages/currents and could have fried C24, esp if it was already compromised. In theory the amp should protect itself but if there's a fault elsewhere that could prove fatal. If there's no output load the power supply has to absorb the output power and if the PSU was already compromised through leaky caps, well ....

Chances are we'll never know, but my gut feel on this is to cut your losses...

edit: Humming is often a sure sign of a dying power line decoupling/smoothing capacitor...
 

Thread Starter

Hawkeyez

Joined Jul 31, 2022
7
Thank you very much, yeah I don’t really know much about this stuff, maybe I’ll just put it back together, keep using it to set my stereo receiver on and watch for a deal down the road.
 

Thread Starter

Hawkeyez

Joined Jul 31, 2022
7
Update, the electronics store could only match up a couple transistors and there was another component I didn’t notice that was also burnt so something happened and most likely took everything out. Cut my losses, learned a little bit and I’ll maybe just find a plate amplifier to replace it with when funds allow. Thanks for the help.
 
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