CA-1010 -30Vdc output phono stage

Discussion in 'Yamaha' started by mbz, Sep 10, 2017.

  1. mbz

    mbz AK Subscriber Subscriber

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    Intermittent problem where approx -30Vdc output from right channel phono stage
    (between FR104, FR106).

    Power rails ok +/-31Vdc. TR110, 12, 14, 16, 18 replaced. D102 (VD1212) replaced.

    Recaped, solder joints/bridges/shorts checked ok.

    Approx -30Vdc on FR102 (either side), FR102 replaced with metal film
    TR112 Vb-e approx 0.2Vdc
    TR114 Vb-e approx 0.0XVdc
    TR116 pulled, still high dc present.

    TR106,8 Vb-e's look ok 0.6-0.7V, b&e voltages in line with other channel

    TR104b approx 12Vdc
    IC104 pin 6 approx 14.6Vdc

    Plan is to replace IC104(2SK100) with other channel

    Has anyone come across this problem before, ie, high dc on phono stage?
    Also, 2SK100 is no longer available, having problems finding the datasheet (yamaha internal).
    I would expect that these are two closely matched FETs. Any significant drawback with
    replacing the IC with individual FET's? Recommendations? Donor amps are rather expensive in AU.
     
  2. avionic

    avionic " Black Knights " Subscriber

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    Are these 7 pin SIP's ? If so PM me.
     
  3. avionic

    avionic " Black Knights " Subscriber

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    Yamaha C-4 has two of them.
     
  4. mbz

    mbz AK Subscriber Subscriber

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    Problem confirmed, switched IC103 and 104, abnormal voltage moved to left channel.

    AK search did not reveal much. Talk of someone having the datasheet, appreciate a
    copy or parameter details. DIYAUDIO post suggests 2SK389 or 2SK170 (both obsolete)
    as possible replacements, maybe work off those datasheets???
     
  5. avionic

    avionic " Black Knights " Subscriber

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    If you have a Peak DCA you can check each FET.
     
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  6. mbz

    mbz AK Subscriber Subscriber

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    Sounds like time to buy some more test equipment.

    This fault was particulaly annoying, amp would power up ok, phono stage fine for anywhere 1sec-10minutes then fallover
    and then recover or even stay faulty. Intermittent/inconsistent=annoying.
     
  7. avionic

    avionic " Black Knights " Subscriber

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    Pretty much slamming the rail to output.
     
  8. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    you said it is 2SK100
    Which one ?
    2SK100 (IE100600)
    2SK100A (IE100900)
    2SK100C (IE101130)
    2SK100D (IE101140)

    ?
     
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  9. avionic

    avionic " Black Knights " Subscriber

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    According to Hoyle . IE100600 are the gems in the CA-1010. However as for the parts list in the C-4 manual says IE101140. But physically looks like a IE100600. ( Y K100 72 )
     
  10. avionic

    avionic " Black Knights " Subscriber

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    With a dab of white paint. Color code perhaps ?
     
  11. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    Yes , like in A1
     
  12. avionic

    avionic " Black Knights " Subscriber

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    I see .. said the blind man.:biggrin:
     
  13. mbz

    mbz AK Subscriber Subscriber

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    First up, thanks for all the input, greatly appreciated.

    I do have an A-1 that I had planned to refurb (one day). I'm tempted to lift the 2SK100 from that and investigate a discrete solution for the A-1.
    My main motive for participating in AK is to learn, maybe time to learn about FETs....

    Can confirm that it's the 2SK100 (IE100600). So a datasheet or parts recommendations (SMD ok) would be appreciated.
     
  14. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    Informations coming from A1 service manual

    2SK100.JPG
     
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  15. zaibatsu

    zaibatsu Active Member

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    If the 2SK389 will work for you, I can pull one from a parts amp of mine and throw in an envelope.

    Let me know.
     
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  16. mbz

    mbz AK Subscriber Subscriber

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    Thanks for the effort guys. Really chasing the FET's characteristics IDSS etc... I have not "studied" FETs but they appear to be just a choke device, ie,
    voltage at gate restricts flow between S&D. That said makes me wonder what impact if any they have on sound quality, by that I mean the IC package\versus discrete items. OK the IC will be closely matched pair but discrete FETs should(?) work. Like I say, time to learn about FETs...
     
  17. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Last edited: Sep 12, 2017
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  18. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    OK the IC will be closely matched pair but discrete FETs should(?) work

    may this confidential datasheet will help you .....to choose your discrete FET

    2SK100-datasheet.JPG
     
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  19. mbz

    mbz AK Subscriber Subscriber

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    Oldsansui441, thanks for the offer on the 2SK163, need to do some homework first. Like I say, I'm treating this as a learning exercise.

    Clinic-audio, brilliant, thank you.
     
  20. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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