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TIP: Humming PC speakers

Community Veteran
Posts: 14,014
Thanks: 539
Fixes: 9
Registered: 01-08-2007

TIP: Humming PC speakers

Hi Guys
Just thought I'd share this tip as it's just allowed me to save a 5.1 PC surround sound system from the landfill. The system was donated from a member of my local freecycle scheme. See http://www.freecycle.org for details.
It was humming rather badly on 3 channels. When I say badly I mean annoyingly bad. You could drown it out with music but when silent you'd be quickly annoyed.
Anyway after tons of googling the most obvious problem appeared to be a ground loop issue. I was certain this wasn't the cause as I'd tried several sockets in our home and it made no difference. The speakers themselves were not at fault either as I'd tried all of them and concluded it was just 3 channels affected.
By pure chance, I came across a site where someone had a totally different make of 5.1 system but had a similar issue. It turned out he had a leaking electrolytic capacitor which when replaced cured his issue.
So, I figured I had nothing to loose and took my sub apart. I removed the PCB and sure enough I found a 4700uF 16V electrolytic cap which was bulging. According to wikipedia this is due to large numbers of caps being produced with the wrong formula that was stolen years ago in order to reproduce them in china/japan.
Anyway I sourced a replacement cap rated at 25V from the local TV repair shop. I desoldered the old cap and soldered the replacement into place observing the correct polarity. Due to it being a little larger I had to bend it over and lay it down in order for the PCB to fit back in through its slot.
I then turned on the power supply, plugged in a speaker and silence! Nothing but pure silence.
So guys, if you have a nice speaker setup which starts to mysteriously hum, have a quick look at the capacitors and see if any of their tops look like they're balloning upwards. It's less than a 15 minute job to fix and it'll save sending the stuff to the local landfill and also save you some £'s in these hard times!
I need a new signature... i'm bored of the old one!
6 REPLIES
Community Veteran
Posts: 26,432
Thanks: 684
Fixes: 8
Registered: 10-04-2007

Re: TIP: Humming PC speakers

I had to replace a Dell MOBO because of those damned capacitors! Angry
jelv (a.k.a Spoon Whittler)
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Community Veteran
Posts: 14,014
Thanks: 539
Fixes: 9
Registered: 01-08-2007

Re: TIP: Humming PC speakers

Yeah, I've done that too...
Wouldn't it of been cheaper to replace the caps? I suppose I should of done that at the time but I didn't have any floating around.
I need a new signature... i'm bored of the old one!
Community Veteran
Posts: 26,432
Thanks: 684
Fixes: 8
Registered: 10-04-2007

Re: TIP: Humming PC speakers

(a) There were quite a few on the board that were domed and no idea which had failed
(b) Replacing caps requires certain equipment and skills - neither of which I have
(c) Paying someone else to do it would have cost more than a new MOBO - with no guarantee of success!
jelv (a.k.a Spoon Whittler)
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pd
Grafter
Posts: 235
Registered: 09-05-2008

Re: TIP: Humming PC speakers

Interesting post.  I have had to replace two motherboards with this problem, on one of them every capacitor on the board had burst open and I couldn't for the life of me figure out why.  I even replaced the power supply for that one thinking it may have been the culprit.  I was thinking over-voltage, surges etc.....  Now we know - thanks okrzynska.
jnwright
Grafter
Posts: 281
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Registered: 05-04-2007

Re: TIP: Humming PC speakers

There is a website, Badcaps, that has a well subscribed forum devoted to the problem of electrolytic capacitors. I cheated - got another new identical mother board on eBay, popped it in, set up the bios parameters and rebooted!
Community Veteran
Posts: 14,014
Thanks: 539
Fixes: 9
Registered: 01-08-2007

Re: TIP: Humming PC speakers

Quote from: jnwright
I cheated - got another new identical mother board on eBay, popped it in, set up the bios parameters and rebooted!

Lol.. I've come close to that a few times myself actually. Cheers for the link!
@pd: No problem. It's not just a one or two companies affected by the bad capacitors that were made. I'm afraid they've spread all over the world as cheap replacements for american parts. There are little caps bulging and leaking all over the world thanks to the japs nicking the formula for the ingredients... minus a few details to complete the process. The worst part is there is no way of knowing when they will fail, what devices they are in, etc.
Just goes to show that sometimes these things are far easier fixed than you'd realise. I was about to dump these speakers until I decided to take the sub apart. It was only then I realised it should be an easy fix!
I need a new signature... i'm bored of the old one!