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5.1 Ultra - Loud Humming - Control pod or amp?


DonnieZ
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My set of Promedia 5.1 speakers has developed a loud humming recently. Previous to this for maybe the last year, there was a very slight humming that could be heard faintly in the background but now it's very pronounced. I can still hear the audio produced by the computer, however the humming is present and at the same level no matter what the volume on the control panel is set on. The hum is also present when using headphones but does not come out of the speakers when headphones are selected on the control pod.

This leads to me believe it might just be a control pod issue. Is this common? I see a lot of posts / websites referencing amplifier repair but not for this exact issue. I haven't found a place to source a new control pod other than Klipsch to try.

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  • 3 months later...
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  • 4 weeks later...

The hum is almost certainly from one of two 100mFd 35 volt capacitors on the main board next to a pair of small, black heat sinks. You have to be careful removing the old capacitor that you don't damage the leads--they are a bit difficult to access with a soldering pencil. I always replace these as part of every repair--the hum is so common on older panels. I recommend using 105 degree Celsius capacitors, in place of the original 85 degree rating. I also bend into a "Z" (offset) the lead that will be closer to the heat sink so that the capacitor is mounted as far from the heat sink as possible.

The control boxes on eBay vary widely in price. One sold for $82 plus shipping this week; another sold for $24 something and shipping.

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  • 1 month later...

I signed up for the forum just to send a BIG "thank you" to stpete cooling and to give a little more colour to the solution to the loud hum.

Your diagnosis of the problem causing my 5.1 system hum was spot on.

The hum started about 2 weeks ago, had become progressively more prominent and had finally become intollerable. I had a notion that it was a component going "soft" with heat but where the heck to start.

I found stpete's post, took a trip to Radioshack to purchase 2 replacement caps (less than $3) and dragged out my needle nosed iron and solder sucker. The components are indeed painful to replace with the mainboard in place (the edge of another board is place directly over the solder joints) but with a bit of finesse you can get an iron and solder sucker in there (long nose varieties make it easier). The trick is to use a small iron but leave it on the solder joint for 20 seconds or so to ensure that the solder is fully molten before you start to put some leverage on the caps to remove them. This is especially important on the inner of the two caps because it is connected to tracks on both side of the board. If you were to leave the iron on for too short a period before starting to attempt to remove the cap then it is quite likely that you might rip the track from the board. Although not a terminal problem it would add significant additional work to rebuild the circuit from separate conductors.

With the caps replaced the system is running fine once again. I now realize how much i use my Klipsch speakers and how much i appreciate them.

It strikes me that Klipsch should be ashamed of the poor design of the boards in this, otherwise excellent, product. Putting passive components in such heat-soaked locations is poor design. My caps must have literally cooked by the semiconducts they serve. These problems are the result of careless design.

Anyway - end of rant. My system is back to its former glory and i am happy.

Thank you once again.

Marc

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I must also extend a huge debt of gratitude to stpete cooling's advice above. $2.79 and 20 minutes with the soldering iron and my 7 month dead Promedia 5.1's are back to life!! I probably owe an apology to my wife who was trying her best to hold the light for me all while putting up with my obscenity laden rant at the difficulty of this job for me....

I've had my ProMedia 5.1's since 2003 or so, maybe 2004 - I don't really remember. Though this job royally sucked and I'd be embarrased for anyone to look at the results of my soldering skills, 20 minutes and $2.79 after 7 years of constant service is OK in my book. This community is awesome and I'm awed by the amount of knowledge that's shared here.

Thanks again and if they turn out to need anything else, I'm probably sending them to stpete!!

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  • 6 months later...

How difficult would you say it was for somebody that maybe only took an electronics class in High School about 15 years ago and whos last Soldering venture was with a mod chip on a PS2?

This issue sounds exactly like what I've been dealing with and would really like to fix it myself. Since I'm ready to ditch the Sub/Amp altogether if I can't fix it, I'm willing to try anything. Do you have any pics or your board that may help to paint the picture for me?

Thanks!

Calen

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Replaced the capacitors tongiht, works perfectly! stpete cooling you nailed it. user_IsOffline.gifTopMarc and DonnieZ if it wasn't for you guys I wouldn't have even tried to replace them. Thank you all.

To anyone else out there with the same problem. If you're thinking about replacing them on your own, take note of the above comments. It's a REALLY tight space to work with, the only saving grace is that there's alot of room on the board it's not crammed tight like a computer part would be. There was no visual damage to the Capacitors so going in I didn't know for sure that was the issue but turns out the humming is gone.

Love these speakers and was dreading the repair bill until I wonder upon this thread.

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  • 1 month later...

Thanks for the great information. I also created a new account just to say thank you. Wanted to pass along where I found mine.

I found (hopefully) the correct parts at http://www.digikey.com/ search for part number - P5551-ND

Product description is "CAP 100UF 35V ELECT NHG RADIAL"

I also found a simular one at radio shack, but it's rated for 80 or so C (it says F on the radio shack website, but that has to be a typo), and I'm going with the advise above and getting one that can stand up to more heat. Also, they are only 30 cents each (+ shipping of course).

Please let me know if I ordered the wrong part. Plan B is to take my amp out back and put some bullet holes in it.

Thanks,
Mark

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  • 4 weeks later...
  • 2 weeks later...

Would this also apply to the original ProMedia 5.1s? I suspect the control pod because the humming in my rig is in the headphones with the main amp disengaged... old swelled up caps are a sure bet given the age of my system, but I confess that I don't know exactly how the pod interacts with the amp... I always assumed it was a preamp of sorts. Would I be hearing a constant hum (regardless of volume) in the headphones even though the amp is disengaged?

On a side note, I've always hated the pop in the mains when switching from the headphone jack. Shame there's no easy way to fix that since I'm cracking the board anyway.

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I've never opened up the control pod on mine. I bought my 5.1 promedia system probably 7 or so years ago brand new, maybe a little longer. The caps on the board for my amp looked perfect, no swelling at all or any other visual evidence that something was wrong, but they were totally failed after I cooked them in a hot office for a few days with zero ventilation. With how cheap these caps are, I'd do the fix described above regardless just by default. They are absolutely a weak link on the board. It looks like it isn't a cure all for everyones issues, I was lucky. If you have a decent multimeter, check out how to test your capacitors, then regardless of where you run into them, you'll be able to determine if they are viable. This site has an ok primer on how to do that towards the bottom of the page. http://www.ohmcheck.com/capacitor.htm

I'm assuming you've eliminated your headphones themselves as a cause of the hum by plugging them into other devices, to include directly into your sound card on the computer. If you've elimintated the amp as a source of the hum, as well as the headphones themselves, and your sound card too, I'd crack that control pod open and start testing it, or if you don't mind extra soldering, just start replacing any caps in there by default. They are cheap enough. That being said, I'd imagine there are other components in the board, and certainly in your 'unique' environment that can introduce hum. Sorry that probably wasn't much help... Anyways, good luck

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Thanks Habersham, your post was more helpful than you give yourself credit for. As far as testing, it is not affected by either the PC volume controls nor the control pods volume pot; it does not emanate from the computer the sound persists when the computer is turned off and even unplugged but the speaker system is on; and it does not appear to be related to noise on the circuit. I have disconnected all electrical devices from the circuit the amplifier is connected to and the hum remains. I have also run an extension cord to a different circuit in the home and the hum was still present. The headphones themselves are hum-free when attached to any other source, a relief given that they're fairly high-end Sennheisers. I'm unclear on the relationship between the control pod and the amp; my thinking is that if the hum is in the headphones straight from the pod, that's where it has to originate - somewhere in the preamp circuit. That makes sense to me because the amp would pick up any hum in the preamp circuit; what I don't fully understand is why it is not affected by the volume pot. It's just... there.

Based on your input, it sounds like it's cap-sweep time. That can't be a bad thing regardless, I bought the system new about one year after it was released so it's got some miles on it, and as you mentioned... caps are cheap. Thanks for the link, I'm going to break out the multimeter and soldering pencil and get to work.

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  • 6 months later...
  • 1 month later...

I joined the site just to say thank you to stpete cooling. For others reading this I will describe my problem along with some tips on fixing this issue.



Firstly, a description.



Much like everyone else on this thread, I had a loud humming noise coming from both my speakers, and from the headphones when connected to the pod. Unlike others, I didn't notice a low hum that got progressively louder, the hum was just there one day. The volume of the hum was quite loud, and did not change in volume when I played with the volume knob.



Fixing the problem.



I'm not going to go too in-depth, mostly because I didn't think about taking pictures while I was fixing it. I will say that my skills at soldering are very crappy. I've never actually soldered anything to a circuit board before, nor have I un-soldered something from a circuit board. With that said, as long as you have a steady hand and have the basics of soldering down, this is easy.



Radioshack carries the capacitors you need. They were 1.49 dollars each when I was there (some 20 cents more expensive then other posters claimed, but I also live in Los Angeles). You will need capacitors labeled as 100mF 35V. The m is actually a mu, so it's rated at 100 micro farads. I only saw capacitors that could handle up to 85 celsius, unfortunately. According to other posters it's preferable to get 100mF 35V caps with a 105 celsius rating. Also, being the novice that I am, I bought axial capacitors. This means that there is a wire coming out of both ends of the capacitor. I believe that the stock capacitors are coaxial, i.e. both wires come out of the same end. Apparently, either one will work.



For novices like me, it's important to know that capacitors have a positive end and a negative end, as I found out (and should have remembered from my general chemistry class, but didn't). Wiring the capacitors in reverse order can be bad. The circuit board has two holes and one has a plus sign next to it. For axial capacitors the capacitor should have a band of arrows running down it. The arrows point to the negative terminal of the capacitor. By process of elimination, the other end is positive.



I've decided to skip explaining how to get the amp out of the sub, because if you can't figure that out, you probably shouldn't be trying to replace the capacitors on it. So, once you've removed the amp you will see two black heat sinks on the main board. the main board has a series of other boards running perpendicular to it. IN BETWEEN these two black heat sinks (I emphasized that so it'll be easier to identify the right area) you will see two capacitors. The next part is removing the capacitors, which I'm sure each person has their own technique.



I grabbed a pair of needle nose pliers and grabbed the capacitor with it. On the other end of the board I applied the soldering tip to the one of pins of the capacitor. I heated it for about 10-15 seconds and then bent the capacitor to one side to get the pin free from the board. I twisted it a tiny bit, then did the same to the other pin and the capacitor came free. Rinse and repeat.



The next part just involves making sure that you use a desoldering device to remove the old solder so that the new capacitor can easily be placed on the circuit board and then soldering in the new capacitors. Make sure you've got the polarity right, and BAM! All should be well!



From start to finish it took me about 30 minutes.

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  • 2 months later...
  • 1 month later...

Add me to the list of greatful ProMedia owners. First time ever electronics repair but with the information and advice in this thread I was able to do the job in 30 minutes for 60 cents in parts. It does not look pretty, but the solder seems tight and shiny. AND, my speakers are silent. I don't recall them being this quiet when new way back when.

Thanks to those of you who wrote the long posts - they got me through. And the short posts built confidence.

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I found this post pretty quickly from a Google search as the humming from my Promedia Ultra 5.1 system became too loud to enjoy the system any more. Thanks for all the info. In my case it appears that two capacitors on one of the amplifier boards (location labels C517 and C518) may be the culprit. They are the only ones exhibiting any physical signs of failure. I have a uploaded a picture of them here: http://www.flickr.com/photos/aharden/7125703883/. From reading the rest of this thread, it appears that the caps that most have replaced are the ones in locations C35/C36). I'm tempted to replace those as well, but I went ahead and ordered the 47mF/50V caps from Digi-Key similar to the ones referred to earlier in this thread. I went to Radio Shack first but they didn't have the caps I needed. I'll attempt the repair later this week assuming I get the parts in a few days. Thanks for all the information!

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