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M4 output transistors??

Discussion in 'Yamaha' started by ferninando, Sep 9, 2018.

  1. ferninando

    ferninando Lunatic Member

    Messages:
    12,462
    Location:
    San Jose Ca.
    Hi all.
    I have an M4 power amp with a major problem. Right ch. output heatsink gets super hot while the left one stays room temp.
    So I'm thinking Output transistor short.
    But before any disassembly to indentify the types of output trans. visualy, I would see if anyone here can tell me
    what their type #s are. 4 per ch. And even if they are still available or good substitutes.
    Any info is welcome and appreciated.
    Thanks.
     

     

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  2. captouch

    captouch AK Subscriber Subscriber

    Messages:
    4,528
    Location:
    Bay Area, CA
    ferninando, does the amp make music on the hot channel? If so, then I'm thinking bias just needs to be adjusted on both channels so both get warm, but not hot/cold. If there's no sound out of the right channel, then maybe the output transistors are bad.

    I'll take a look to see if the bias setting procedure is available.
     
  3. captouch

    captouch AK Subscriber Subscriber

    Messages:
    4,528
    Location:
    Bay Area, CA
  4. ferninando

    ferninando Lunatic Member

    Messages:
    12,462
    Location:
    San Jose Ca.
    thanks Cap for the link and svc mnl.
    Once I discovered the hot heatsink I didnt go any further . stopped all doing till I can find out more on the transtrs.
    so do not if it plays on the hot ch. do know its too hot to touch.
    Its the M4 amp I bought when I bought the C4 preamp.
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,703
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    Fort Dodge, Iowa
    Check the bias adjustment !
     
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,703
    Location:
    Fort Dodge, Iowa
    ...
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,703
    Location:
    Fort Dodge, Iowa
  8. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,703
    Location:
    Fort Dodge, Iowa
    If the protect relay "clicks" shortly after power on. The outputs are not shorted.
     
    TWTRTECH likes this.
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,703
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    Long time discontinued.
     
  10. clinic-audio

    clinic-audio all on YAMAHA untill 1990

    Messages:
    2,180
    Location:
    France
    I have an M4 power amp with a major problem. Right ch. output heatsink gets super hot while the left one stays room temp. This mean for me that you have sound on both channels
    So I'm thinking Output transistor short. No ! if 1 output transistor is shorted you can't get sound on the right channel because the fuse burn
    But before any disassembly to indentify the types of output trans. This not necessary to delete anything to get this info , it is in service manual
    visualy, I would see if anyone here can tell me read the SM (2SA1050 Toshiba and 2SC2460 Toshiba )
    what their type #s are. 4 per ch. And even if they are still available or good substitutes. Why are you talking about replacement of rare working output transistors ??
    Any info is welcome and appreciated. Here is what you need to know : if one channel is overheating this is because there is something wrong with the bias circuit (this do not mean that you just need to re-adjust it ) ! I think that you are in front of a defect parts in this bias circuit and you have to find which one .
    Once you have replaced the bad part you can switch the power on and re-adjust the bias but only after that .
    Re-adjust a bias is not normal because the factory adjustment can't moove alone and that's why I tell you that you have something wrong in your bias circuit !
    I am pretty sure that if you don't want to follow my advice and make a bias re-adjustment without doing anything else inside this unit , you will not be able to get the recommended value

     
    milo63 and TWTRTECH like this.
  11. ferninando

    ferninando Lunatic Member

    Messages:
    12,462
    Location:
    San Jose Ca.
    ok clinic I will investigate it.
    thanks for your info.
     

     

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  12. ferninando

    ferninando Lunatic Member

    Messages:
    12,462
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    San Jose Ca.
    never mind. operator error
     

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