[Quinn] Resurrects An Amplifier That Experienced Death-by-capacitor

[Quinn Dunki] is adding wireless audio to all of the rooms in her home. She’s going with Airplay, snatching up used or refurbished Airport Express units because of their ability to work with both her existing WiFi and the Airplay protocol. The last piece in the puzzle is to get an Amp and she chose the small unit seen above. The problem is that it was dead on arrival and she couldn’t get the company to respond to her issue. So she cracked it open and fixed it right up.

The offenders are the three electrolytic capacitors at the top of the picture. She took some close-up images of each and you can’t miss the fact that they’re blown out. These are often among the higher price-per-unit parts and manufactures try to pinch the penny as much as possible. Add to it the heat in a small enclosure like this one and you’ve got a failure. [Quinn] dug through her junk bin but the size of the replacement had to be a perfect match so she ended up putting in a parts order. The new caps fit and work perfectly as you can hear in the clip after the break.

28 thoughts on “[Quinn] Resurrects An Amplifier That Experienced Death-by-capacitor

  1. I would have bet money before reading the article that the caps would be CapXon…surprise! I wonder how many hundreds/tens of thousands of devices have been thrown out by less-skilled persons due to bad capacitors. Good job, Quinn!

    1. Not only does it appear that it was a used item that got sold/shipped as new, but the capacitor failure likely happened one of two ways:
      1.) Under QA test at the factory in China (odds are good that’s where it was made, though its anyone’s guess)
      2.) Under connection in “bridged” configuration. As far as I know (enlighten me pleas) most “Class D” amps will not operate properly in “bridged mode” (where both stereo channels are joined to power a single speaker). This particular product shows that in can be used in such a fashion. Looking at the close-up of the circuitry, it appears that they’ve added protection to enable the bridging option, but I’m not convinced that they’ve done it in such a way as to be bullet-proof. Granted, I’m also running on lack of sleep at the moment so I could be all wrong, but on very quick glance, I’d say that it looks like it was pushed too far by whomever first had it before it was sold/shipped to Quinn as new.

      Thankfully, she had the good sense to try fixing it… great write-up, useful article, nicely done. Regardless of how cheaply made, Class D amps can usually be rendered quite useful with a little time and effort, and the quality of their sonic output ends up being outstanding! I’d love to see more of these kind of articles (Audio/Video and circuit work) here on HAD, so go get a Class D amp, crack it open, figure out how it ticks, and then document the process of making it sound better, building a better enclosure, etc… :-)

      1. Hi Grady,

        Here’s a few to get you started:
        1.) http://www.irf.com/product-info/audio/classdtutorial.pdf
        2.) http://sound.westhost.com/articles/pwm.htm
        3.) http://www.eetimes.com/electrical-engineers/education-training/tech-papers/4213805/Class-D-Amplifier-Design
        4.) http://hephaestusaudio.com/media/2009/12/How-to-Design-a-Class-D-Amplifier.pdf
        5.) http://www.ti.com/lit/an/sloa031/sloa031.pdf

        And remember, Google search is your friend. To find these (all on the first page), I googled the phrase “Class D Amplifier Design”. If you’re just getting started, it might be good to build a class D kit first (doesn’t have to be high wattage… a little goes a long way with a Class D amp and a set of average or better speakers), so you get a rough idea of the basic circuit(s), filtering, power supply requirements, etc… Once you’ve built one, you’ll be able to grasp the written side of things a bit easier and you’ll have something to refer to. You can find buildable Class D’s online – google “class d amplifier kit”, or check out the nice folks over at Parts Express (I have no connection to them, but I shop them periodically and have always had a great experience) for one option: http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-322

        Good Luck and Happy Learning!!!

  2. You’d be surprised how common of a problem bad electrolytic capacitors are. I have seen many lcd tvs and monitors that aren’t working because of one or more dead electrolytics. Usually replacing them is enough to bring the monitor or tv back to life.

      1. my brother works for a private organization that gets lots of donations of older computers(barely run XP) and they have obviously bad caps. he was telling me about them and suggested i could help with replacing them. any tips?

      2. Although there is a lot of information overloaded with information best suited for the page for electrolytic capacitors, but LOL @ this at the top of that Wikipedia page;
        “This article may be too technical for most readers to understand. Please help improve this article to make it understandable to non-experts, without removing the technical details. The talk page may contain suggestions. (July 2012)”

      3. @superbrainak, I found that the easiest (and most effective) method for replacing caps on a motherboard is to “chop” the offending cap off at its connection leads (or pads) above the actual motherboard, then solder the replacement to the original cap’s leads/pads. It beats trying to fiddle with the motherboard itself, and more motherboards tend to survive this treatment.

        Just thought I’d share that with you…

  3. I got the impression from her site that the amp was new. Obviously, since the caps have failed that is not the case. I have got no problem buying broken stuff especially if it won’t power up and I know it has electrolytic caps. But generally I know before I buy.

    Replace the caps first then trouble shoot. Did that with a DTV to Analog TV converter and it worked like a charm.

    Nice work.

  4. It seems like bad caps are always the culprit. I repair amps on the side, and 99% of the time, the fan gets crapped up, and the caps fail. Occasionally it’s something else…but it’s rare. I’ve seen people replace the caps themselves, and use capxon. When they can’t figure out why they keep burning up caps, and they bring it to me to fix, I open up the cover, and just stare at them. By far the worst brand I have ever encountered. There may be one or two that are worse…but not by much.

  5. Yes, they are evil. But not the only make, Sa*xon also fail as well.
    I am so going to make a special device which detects water/hydrogen buildup in capacitors for a quick “yes its fscked” diagnostic without dismounting every capacitor affected.

    I have also noticed a tendency for manufacturers to avoid fans as a cost cutting measure which results in bad caps due to overheating thanks to 85c caps being used where 105’s should be.

  6. Having started on tubes, I have watched as caps slowly became the most frequent failure component. Lytics for sure. Whatever makes the best time-fuse that also is very cost effective, use it.
    Anyone notice the “face” in the the photo at the top! Fuming off the top about the “caps on” it’s head?

    Other bad caps are ones with 3 letters usually consonants like SMC.

  7. -1) i use capXon (crapXon) and TEAPO (CHEAPO) interchangeably; aka never!

    0) despite what people on here have hinted at,
    … ask a tube repair technicin, one that has repaired tube filter caps for 25 years …

    1) dont use capXon/TEAPO

    2) if it has capXon/TEAPO, change them, even if working

    3) if it has capXon/TEAPO, dont buy it, unless you know how to “repair it”

    4) dont operate capXon/TEAPO equipment in the summer/out of AirConditioning

    5) i will not be held responsible if a capXon/TEAPO equipment catches fire and burns your house down.


    7) capXon/TEAPO is only here to hurt you, they do not love you, they are your enemy, they do NOT want you to have fun.

    8) if you think the fire department will tell you that your house burned down because China ripped you off by 73 cents, THNINK AGAIN!

    1. Have we all been around these infernal machines so long that we now endow human attributes to these BYOTCHEZ!

      Leave CapXon & Teapo alone. Do you think for a second that such manufacturer would sell to the Chinese Military inferior components and expect to live long?

      Would it not be surprising that the engineering choice of a lower grade of cap. combined with above 70degC heat and possibly noisy P/S exceeded the original parts design (to save costs) by a long-shot?

      I’ve seen TV’s where none of the CapXon P/S caps failed (5000hr parts), yet the MPU was brought down by a lowly 100uF-16V SMD cap – an obviously incorrect grade?
      Follow the voltages & find the faults! Isolate, isolate, isolate. Consult datasheets.

      I’ve also seen caps in OEM P/S’ with a blown cap silkscreened incorrectly on the parts side. No wonder it blew in the first place!

      Electronic devices are no different than cars in respect of human error starts at the factory (and possibly management with an overeager eye to save company money to be rewarded). :)

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