Sansui AU-7900 - Big POP when Powered off ONLY with Tone Control ON

Discussion in 'Exclusively Sansui' started by Zekeman, Sep 29, 2017.

  1. skippy124

    skippy124 AK Subscriber Subscriber

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    Hi Zeke,

    Are the measurements on the base and emitter of TR02 correct?
     
  2. Zekeman

    Zekeman AK Subscriber Subscriber

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    Bias was dialed-in correctly a couple of weeks back. I'll recheck it.

    I'll post the other findings tonight. Thanks
     
    Last edited: Oct 4, 2017
  3. vigman

    vigman SUBSCRIBER

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    A spark means either Hi current or Hi voltage being removed from a load.. at amp idle you should have neither....
     
  4. Robisme

    Robisme Sansui Enthusiast Subscriber

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    I have been watching this thread hoping for a clue for an issue I am going to be chasing. I have a 7900Z receiver doing the exact same thing.

    So it can happen. I don't see how though. DC offset is 14mv, but with tone on, a very loud pop on power off. Relay opens instantly.
    Both channels. Tone off, no pop.

    My first thought is power supply issue because it's in both channels, or a bad ground.

    Time will tell, I hope.

    Rob
     
  5. Zekeman

    Zekeman AK Subscriber Subscriber

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    The power supply is OK it's just a tad high. Not quite sure if that is significant but its not wildly off and it is consistent across all values.

    When I get home I'll try the latest suggested ideas toward resolving this.
     
    Last edited: Oct 4, 2017
  6. Zekeman

    Zekeman AK Subscriber Subscriber

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    Yes
     
  7. Zekeman

    Zekeman AK Subscriber Subscriber

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    To answer your other question - the amp is properly biased at 18mV.

    Regarding R-73/74....I'm getting some fluctuating values of approximately -21mV, -19mV
     
    Last edited: Oct 4, 2017
  8. vigman

    vigman SUBSCRIBER

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    Sorry 2596 the protect board.. Input to the relay...
     
  9. vigman

    vigman SUBSCRIBER

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    Again so I'm clear the POP only happens on power off and you are in tone on or tone and filters on .. but is OK with both tone & filters off?
     
  10. Zekeman

    Zekeman AK Subscriber Subscriber

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    Exactly yes
     
  11. vigman

    vigman SUBSCRIBER

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    If the amp is running and you switch in & out of tone and or filters No pop ?
     
  12. Zekeman

    Zekeman AK Subscriber Subscriber

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    No pop
     
  13. skippy124

    skippy124 AK Subscriber Subscriber

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    TR02 is NPN, 10V on the base and 11V on the emitter?
     
  14. Zekeman

    Zekeman AK Subscriber Subscriber

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    Yes I believe I have a c1845 in there .
     
  15. skippy124

    skippy124 AK Subscriber Subscriber

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    Orientation OK?
     
  16. vigman

    vigman SUBSCRIBER

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    Wow this is strange......Measure the PS for the output section, does it glide down or DROP OUT when you kill power ??
     
  17. Zekeman

    Zekeman AK Subscriber Subscriber

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    Will do
     
  18. Zekeman

    Zekeman AK Subscriber Subscriber

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    Edit: This morning (Sat) I am getting Orientation OK. 11V base and 11V (stable) on emitter and 20V collector
     
    Last edited: Oct 7, 2017
  19. Zekeman

    Zekeman AK Subscriber Subscriber

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    Glides back to 0
     
  20. Zekeman

    Zekeman AK Subscriber Subscriber

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    Here are some additional values taken today and points where the pop occurs.
    AU-7900 POP Pop locations on 2610-2.png AU-7900 POP Pop locations on 2610-2.png AU-7900 POP Pop locations on 2611-2.png
     

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