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Trying to bring Sansui AU-517 back to life

Discussion in 'Exclusively Sansui' started by Dahond, Oct 8, 2018.

  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Interesting, thank you, it looks like the 2 larger white cement resistors are 330Ω - ('330R') and should be 0.33Ω - if I am right this would entirely explain your protection issues.

    Would you please check this and confirm?

    This statement in your first post really surprised me.
    I thought to myself 'WHAT'!!? - but passed over the remark. :)
     
    Last edited: Oct 11, 2018
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  2. Dahond

    Dahond New Member

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    Haha this is stupid.
    You're right. they are 330 ohm.
    I'm quite ashamed not seeing this.

    Not sure about the R47. I didn't change them and the schematic says 2.2 ohm.
    I wil solder them out and check again.
     
  3. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    You are correct :thumbsup: - I was (briefly) mistaking the 2.2K 2W standard resistor (R04) for the 2.2Ω cement resistor (R47) - which should be 2.2Ω. - my apologies. ;)

    Oh, and if you change those 330Ω resistors for the correct value, be careful of the bias setting, be sure to turn it right down before powering on again. Or start up on DBT just to be safe.

    I'll be interested to see what you find. :thumbsup:
     
    Last edited: Oct 11, 2018
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  4. Dahond

    Dahond New Member

    Messages:
    12
    Location:
    Belgium
    IT'S ALIVE
    Oh man this is great! No more protection problems.
    Thank you this is really amazing.
    SO stupid I didn't check the resistors well enough @kevzep
    Thank you so much @Hyperion for taking a look.
    I'm quite happy right now :)
    My wife's going to be disappointed the big sansui SP3500 speakers have a reason to stay in the room now :)
     
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  5. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yay ! - Well Done !! - very happy for you :banana:

    But one question, are the zener voltages OK now?
     
  6. Dahond

    Dahond New Member

    Messages:
    12
    Location:
    Belgium
    Zener voltages:
    Right:
    ZD01 22.55
    ZD02 -23.11

    Left
    ZD01 21.93
    ZD02 -23.30

    Seems like they are only off by 0.6v max
    -> 0.8v on the left ZD02
     

     

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  7. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Well, assuming 5% tolerance components originally, both ZD02's are out of spec' but only just... - you can now properly enjoy your AU-517 but personally I like to see these voltages closer together. Perhaps consider buying some replacement zeners when it is convenient, no hurry, just something to consider. ;)
     
    Last edited: Oct 11, 2018
  8. Dahond

    Dahond New Member

    Messages:
    12
    Location:
    Belgium
    I'm going to reassemble it for now and enjoy for a while.

    I've recapped the powerboard with some cheap caps at first to try and figure out the problem.
    I'll be ordering some decent replacement caps, new zeners,1N4148's, maybe recap the preamp and EQ too in the near future.
    This whole adventure made me realize it would be such a shame to loose the amp but now that I know it's not lost, I can take my time and make sure I get it right.

    Any other things I should do to it to make it live forever? Maybe swap the relay?
     
  9. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yes, good idea - all proper reconditioning should include this.

    Have a look around here on AK at what other AK members have done with their AU-517 /717 reconditioning - especially the excellent 'Leestereo' thread(s) - there is one of his for the AU-717 which you can use as a guide for doing your AU-517 as they are nearly identical. ;)

    There are plenty of others. :)

    In addition, reading the other threads will teach you a lot, there is so much knowledge and experience in those threads.
     
    Last edited: Oct 11, 2018
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  10. Dswankey

    Dswankey Super Member

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    @Dahond

    I'm glad the resident Sansui experts were able to help you out. Congrats! on getting her back up and running.
     
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  11. Dahond

    Dahond New Member

    Messages:
    12
    Location:
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    Leestereo's work looks very nice.
    I will certainly check his threads.
    Here's the assembled 517 with his partners. Thank you very much again. 20181011_141148_HDR.jpg
     
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  12. Leestereo

    Leestereo Super Member

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    @Hyperion is correct, the AU-517 and AU-717 are very similar, in fact they share the same service manual.

    Here are some pictures of a restored/upgraded AU-517:

    power supply 1 restored.jpg

    power supply 2 restored.jpg

    preamp after.jpg

    premain restored.jpg

    F2721 restored.jpg

    F2722 restored.jpg
     
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  13. Dahond

    Dahond New Member

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    Location:
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    Looks amazing @Leestereo
    Why did you increase capacitance in the AU 717?
     
  14. Leestereo

    Leestereo Super Member

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    Location:
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    The goal of increasing the values of the local filtering capacitors is primarily to enhance/maximize the performance of the circuit. Generally, there is no problem increasing the capacitance rating of the local decoupling/filtering capacitor (especially for small values less than 1000µF). IMO, a 2X-3X increase is acceptable for most small capacity capacitors whose function is DC filtering.

    Why increase the capacity of a power supply? It has been argued that a power supply is essentially in series with the stage's output (hence in the signal path), and as such does impact the sound of an amplifier. Nelson Pass uses the analogy of a water reservoir as the power supply and the output stage as the valve that controls the flow of the water: https://www.passdiy.com/project/articles/power-supplies. If you have a poor and/or inadequate supply, the quality and/or the quantity of water is affected. For an amplifier, a poor/failing power supply capacitor (e.g., low capacity, high ESR) may not be able to supply the voltage/current that the output stage is "asking" for. IMO, this is primarily why improving the power supply (e.g., increasing capacity, lowering impedance/ESR) often does impact/improve the sound of an amplifier.
     
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