907 imos .....Blown output mosfets ...need replacements advice

Discussion in 'Exclusively Sansui' started by quadklipsh, Sep 5, 2018.

  1. quadklipsh

    quadklipsh Super Member

    Messages:
    1,156
    Location:
    Lahore, Pakistan
    Well , a sorry thing happened and the amplifier blew its left channel.
    Can i have some good suggestions for the replacements of the MOSFETs.
    T j 405
    T j 115
     

     

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  2. kevzep

    kevzep Its all about the Music Subscriber

    You need to get the right part number, those you listed do not bring anything up.

    If they are TO3 package, forget it, you'll never find them except maybe on eBay....used or fakes...
     
  3. skippy124

    skippy124 Super Member

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    1,614
    Location:
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    The full part numbers are 2SK405 and 2SJ115, these are obsolete devices, and I don't think any of the normal sources would have any stock.
    They are available on Yahoo Japan in matched sets - see link below for an example

    https://page.auctions.yahoo.co.jp/jp/auction/g277696630

    Cheers

    John
     
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  4. kevzep

    kevzep Its all about the Music Subscriber

    Yep, well obsolete aren't they....
     
  5. quadklipsh

    quadklipsh Super Member

    Messages:
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    Is this a dead end for the amp ?
     
  6. restorer-john

    restorer-john Addicted Member

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    Have you taken out all 8? Have you removed and tested each one?

    Do not, under any circumstances buy these devices on eBay. They are all fake I can assure you. No matter how good you think they look- they are fake.

    If you want to see some J115/K405 fakes alongside genuine ones, I can post a few pics.
     
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  7. quadklipsh

    quadklipsh Super Member

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    restorer-john
    please send images before i decide where to order .

    any assistance is welcome .
    Im tilting towards Exicons as Hitachi or any original pull outs is gonna be next to impossible ......if thats the general impression .....
     
  8. quadklipsh

    quadklipsh Super Member

    Messages:
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    The guy who witnessed the burning of the outputs,the smoke and crackling tells me that the amp was up and running for 30 minutes with absolutely no complaints and he had half a dozen friends sitting enjoying music , there was no distortion or noise whatsoever . ... ..

    our minds are in knots what could have caused this ......
    any guesses ?
     
  9. quadklipsh

    quadklipsh Super Member

    Messages:
    1,156
    Location:
    Lahore, Pakistan
  10. quadklipsh

    quadklipsh Super Member

    Messages:
    1,156
    Location:
    Lahore, Pakistan
  11. quadklipsh

    quadklipsh Super Member

    Messages:
    1,156
    Location:
    Lahore, Pakistan
    The block was removed by the tech and he tested the fuse . The fuse was blown n then replaced which turned the right channel ON. but the left has the blown transistors .I wasn't in the workshop so don't know if he tested each ONE OF EM OR NOT ....but looks like the whole block of 8 Mosfets would have suffered .
    ....
    Are we supposed to replace only the 8 of em of the burnt side or do a complete sweep and replace 16 of em for both sides... with the Exicons or the best ones , i wonder which ...
    please suggest and maybe give me a differential diagnoses of why it happened . ...
     

     

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  12. quadklipsh

    quadklipsh Super Member

    Messages:
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  13. quadklipsh

    quadklipsh Super Member

    Messages:
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    Location:
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    Are these fake
     
  14. restorer-john

    restorer-john Addicted Member

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    No, Zelkjo's Mosfets are original. He bought a pile of them from Japan and sells them on to make a few dollars. I even got some from him several years ago. He is trustworthy.

    I'd be going straight to the bias pot and associated circuitry. Many a mosfet amp has taken out all its devices when old bias pots get flaky.

    You will need to remove them all and carefully test them- and the 0.22ohm wirewounds- some may have failed too. On that amp, you'd need to get a bunch of mosfets and match them. It will be an expensive exercise. Forget the exicons, you can get originals.
     
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  15. petehall347

    petehall347 the brandy coffee man Subscriber

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    check drivers etc and the zener gate diodes if they fitted them .
    yes replace all outputs in a channel .
     
  16. Ronito6

    Ronito6 Super Member

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    Kale never deals in fakes. Never.
     
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  17. petehall347

    petehall347 the brandy coffee man Subscriber

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    might have needed a compressor limiter before the amp or may have needed better speakers .. my mosfet amp has blown up for both those reasons .. am sure most dj.s think it is good to have the red lights constantly lit on their mixer .and consequently the amp clipping lights full on .
     
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  18. Tom B

    Tom B AK Subscriber Subscriber

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    The above comments cement my strategy of never buying a unit with mosfet outputs, and truthfully staying clear of attempting to repair/restore any. Transistors have been manufactured for so many years in so many different case styles. There is almost never an issue with finding good replacements in whatever case style you need, but I can't understand why power mosfets came and went so quickly.

    But I wish you luck in your repair journey
     
  19. Pio1980

    Pio1980 AK Member Subscriber

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    Odd, there are any number of pro linear MOSFET amps chugging along with nary a hiccup.
    My present preferences lean to MOSFET linear and digital switch mode amps. Meanwhile, the Marantz 8 tube amp is sidelined.
     
    Last edited: Sep 6, 2018
  20. kevzep

    kevzep Its all about the Music Subscriber

    Came and went so quickly?
    Every large format Concert sound system using the latest technology are all using MOSFET power amps. Nobody uses Bipolar power amplifiers any more, only older systems....
    We have retired all our BJT amplifiers.
     

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