LSI25 amp problem

mlistens03
mlistens03 Posts: 2,767
in Troubleshooting
So yesterday I picked up a pair of Polk LSI25 speakers at my local goodwill, and when I fired them up this morning, the sub in the right speaker wasn’t working. I decided to pull the amp board and take a look inside. The fuse was blown so I replaced it and plugged it in, and immediately one of the things that are the actual amps (can’t remember what they are called all of the sudden, it is one of the four pieces on the side of what I believe is a heat sink) began smoking. I don’t know if the amp powered on when I did that because I was paying to much attention the smoke, but does anyone know what could be the problem and how I could fix it?

Thanks,
Micah
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Comments

  • mlistens03
    mlistens03 Posts: 2,767
    I think I posted this in the wrong place. Sorry!
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    Hello,
    The bass amplifier would have to be repaired or replaced, telephone Polk tomorrow at: 1-800-377-7655 select option 2 for parts.
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  • Airplay355
    Airplay355 Posts: 4,298
    Somebody dumped Lsi25 at Goodwill? Lucky find, broken or not!
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  • mlistens03
    mlistens03 Posts: 2,767
    Ikr? I got them for $50!
    Thanks guys, I will
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  • mlistens03
    mlistens03 Posts: 2,767
    While I was here I thought I would ask, I currently have a Yamaha amplifier that only is able to go down to 6 ohms, will this be a big problem that I have to fix ASAP or something that can wait?
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  • mlistens03
    mlistens03 Posts: 2,767
    Sorry to bump an old thread, but I decided that’s probably better than a new one :smile:
    I got to really looking at this amp yesterday, and I think I might have found a blown resistor, but I’m not 100% sure. It looks a little cooked, but then at the same time it looks like some cr@p just got on it. Do you guys think this guys is blown?
    hoj80xrzpxzj.jpg
    I fall you think it is, do you know the values of this resistor? I can’t figure out how to read it, because everything I find on the interwebz doesn’t agree with what I see on that resistor.
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  • pitdogg2
    pitdogg2 Posts: 25,438
    edited May 2018
    Which one are you referring to?
    Give us a number. Usually a cooked resistor is very easy to tell.
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  • F1nut
    F1nut Posts: 50,542
    20k ohms 1%

    I don't think that resistor is cooked though.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • txcoastal1
    txcoastal1 Posts: 13,281
    If I remember correctly, when my board went out it was around the rectifier
    2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
    Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
    Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
    Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC

    erat interfectorem cesar et **** dictatorem dicere a
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  • mlistens03
    mlistens03 Posts: 2,767
    Sorry I forgot I’m looking at R80, looks like it either is slightly browned or has some form of crap on it.
    Where is the rectifier on the board? I’ve heard of that type of component before, but I don’t know what it is or looks like. Would this be the amp chips on the side of the heat sink?
    4t3z8bggtv42.jpg
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  • msg
    msg Posts: 10,012
    M - was just curious, did you ever have this amp repaired? Are you having a problem with it now, or just having a look around?
    I disabled signatures.
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  • mlistens03
    mlistens03 Posts: 2,767
    It didn’t work when I bought it, and I never got it repaired. I want to try fixing it now, so that it’s will work for the time being, and then they will be worth more when I sell them. I was just looking inside to see what I could see, and test caps/resistors and stuff.
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  • txcoastal1
    txcoastal1 Posts: 13,281
    The rectifier and heat sink I was speaking of, is between the blue capacitor S0143 and the brn/yel cable connector
    2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
    Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
    Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
    Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC

    erat interfectorem cesar et **** dictatorem dicere a
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  • mlistens03
    mlistens03 Posts: 2,767
    I decided this was the thread I should post this in, I found this in my wallet from the LSis:
    9y5lfh7rtyps.jpg
    I guess I stuffed it in my wallet after buying them and forgot about it.
    I’m going to use this as an opportunity to say thanks so much for everything. Thanks for the help everyone, thanks Nightfall for the cartridge for my TT, and most importantly; thanks everyone for the memories.
    Micah
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  • FestYboy
    FestYboy Posts: 3,861
    That sounds very much like a goodbye...

    I hope I'm wrong.
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  • mlistens03
    mlistens03 Posts: 2,767
    FestYboy wrote: »
    That sounds very much like a goodbye...

    I hope I'm wrong.

    Oh you are wrong! You are right that sounds like goodbye! Oops lol sorry everyone for not noticing that.
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  • FestYboy
    FestYboy Posts: 3,861
    Oh good.

    Now back to the task at hand: see if we can't get a service manual for that amp. Amps are fairly easy circuits, but when there's a preamp stage, filtering and shaping circuits, and power rectification, things can get weird and confusing quickly. Best to start on the power supply side, as it's the simplest circuit.

    I'll be getting knee deep in a NAD 7175PE's power circuit myself. It blows a 5A power switch fuse immediately, so a dead short is what I'll be after. From the sounds of it, the same is going to hold true for you.
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  • mlistens03
    mlistens03 Posts: 2,767
    FestYboy wrote: »
    Oh good.

    Now back to the task at hand: see if we can't get a service manual for that amp. Amps are fairly easy circuits, but when there's a preamp stage, filtering and shaping circuits, and power rectification, things can get weird and confusing quickly. Best to start on the power supply side, as it's the simplest circuit.

    I'll be getting knee deep in a NAD 7175PE's power circuit myself. It blows a 5A power switch fuse immediately, so a dead short is what I'll be after. From the sounds of it, the same is going to hold true for you.

    Thanks! I think it is a dead short, because it blows the 5 amp fuse in about 2-3 seconds (I know it isn’t supposed to be 4 amps, but it was all we had on hand at the time). I’m slightly worried that the transformer is the problem, because according to the 3rd party repair guy’s eBay site, it isn’t the only part that can no longer be replaced.
    I have searched and searched the webs for a service manual, but I have yet to find one. Would Polk supplied me with one if I asked?
    Thanks,
    Micah
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