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Are those blown capacitors?

Discussion in 'Audio' started by NikolayM, Jun 15, 2018.

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  1. NikolayM

    NikolayM

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    Jun 15, 2018
    So I have a Harman Kardon home theater system, and the subwoofer(SUB-TS11 is the model) started becoming really woofy(the bass is not deep, it's like it has a lot of mid frequencies that shouldn't be there), and yesterday I disassembled the whole thing and took a look at the PCB and on some places it looks like there are blown capacitors, but I'm not absolutely sure, it might just be glue I'm looking at.
    (I've attached images of what I think could be bursted capacitors)

    Also the volume potentiometer on the sub is really bad, there is a lot of crackling when it's being moved, but the worst part is that, unless I pull the knob back it's like it doesn't even work and the sub is working at close to full volume, should I replace it, or is there a way to fix it?
     

    Attached Files:

  2. bushtech

    bushtech

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    Sep 13, 2016
    I'm no expert but that looks like glue to me
     
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  3. 73's de Edd

    73's de Edd

    2,805
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    Aug 21, 2015
    Sir NikolayM . . . .

    I'm only seeing " hold down " and " tack " adhesives.
    The yellow circle is where they made a mod and held down the part.
    If the control is so bad that it has to be held, that is probably beyond cleaning stage and a mechanical wiper loosening . . . . . . ergo . . . .replace.
    It is designated as VR201 and is a 50K analog taper type.
    There are several switches on that unit related to filtering frequencies. Move them off position 20 + times to get some temporary mechanical / scraping cleaning action on all of them. poor contact action might have onset and be at fault . . .since that cabinet . . . . it do get a shakin' !

    Other than that, can't quite pinpoint any more on your quirky audio onset fallacy. .

    73's de Edd
    .....
     
    Last edited: Jun 15, 2018
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  4. NikolayM

    NikolayM

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    Jun 15, 2018
    Ok it might just be the bad potentiometer, but a lot of the times it's like the sub's volume gets really loud and then it gets back to normal, just randomly, like it's picking up noise from somewhere, and that's without anyone touching the controls.
    Is it possible that there is interference from the cables of the other speakers, because they are all really close to the sub's cable, or maybe the power cables cause they're close too?

    And last question, if I'm going to change the potentiometer, is there a specific one which I should be looking for, or are they all the same?
     
  5. bushtech

    bushtech

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    Sep 13, 2016
    As 73's de Edd has stated it's a 50K analog taper pot, but you need a pretty good match so that it fit's in the hole and knob fit's on correctly (You get different diameter shafts)
     
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  6. NikolayM

    NikolayM

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    Jun 15, 2018
    Nevermind, I just rushed through 73's de Edd's comment and didn't notice he said what the pot was.
    Thanks for the help guys!
     
  7. davenn

    davenn Moderator

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    1,830
    Sep 5, 2009
    yup all pix of glue
     
  8. dave9

    dave9

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    Mar 5, 2017
    You should plan on replacing the POT, but in some cases I have managed to get some working again. Assuming the crude stamped metal shell design with gaps, try spraying some contact cleaner in and rotating it back and forth several times before the cleaner evaporates.

    Next step is take the pot off, bend the metal tabs of the housing up, disassemble and gently bent the wiper out some to provide more friction against the board tracks, and if the grease on the tracks has hardened, clean that off too. Some people then put down a thin layer of dielectric grease, or whatever they have handy whether it be lithium, petroleum jelly, etc. In other words for a one-off application, no sense paying as much for special grease as a new POT costs.

    Another option is use resistors to make a voltage divider to put in place of the pot, then no more crackling ever but is at the fixed volume you choose based on the resistor values, or pick a better quality POT and if it won't fit where the original was, mount it elsewhere with wires connecting it to the circuit board.
     
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