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Repair and Upgrade of a Previously Recapped Sansui AU-555A

Discussion in 'Exclusively Sansui' started by Leestereo, Oct 10, 2018.

  1. Leestereo

    Leestereo Super Member

    Messages:
    2,140
    Location:
    Ottawa, ON
    On the bench is a Sanusi AU-555A that was sent in by an AK member for repair and upgrade. The background on this unit: the owner had this unit recapped (approximately a year ago by a tech local to him), but was less than satisfied with the results. Aside from the lackluster sound following the recap, the owner noticed that there was now a loud turn-on "pop", whereas there were none before. Also problematic was the intrusive background noise with the phono input, and affecting all inputs was the sound dropping out in the right channel. The unit was brought back to the original tech on two occasions, but the issues remained and hence the owner contacted me: "I'm interested in the full restoration, l already have a recap and it's not satisfactory. I can't use it or sell it so let's get it to spec."

    Here are pictures of the recapped unit as received.

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  2. Leestereo

    Leestereo Super Member

    Messages:
    2,140
    Location:
    Ottawa, ON
    The cause of loud turn-on "pop" was a broken trace (indicated by a yellow circle in picture below) on the Main Amplifier F-1266-1 board at a capacitor (C822). This capacitor is part of the regulated supply circuit which feeds the input transistors for the main amplifier. The intermittent sound in the right channel was due to oxidized contacts in the tape monitor switch. Having addressed the functional issues, the next step is upgrading the unit as per this previous thread: Leestereo's Restoration/Upgrade of a Sansui AU-555A.

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    Last edited: Oct 10, 2018
    smurfer77, Hyperion and slimecity like this.
  3. Leestereo

    Leestereo Super Member

    Messages:
    2,140
    Location:
    Ottawa, ON
    Here are pictures of the upgraded 555A.

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    smurfer77, BigElCat, Hyperion and 7 others like this.
  4. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    48,556
    Location:
    Hertfordshire, UK
    Lovely, really excellent.

    Perhaps a forgone conclusion, :thumbsup: but it'll be nice to hear a follow up from the owner regarding how it sounds now after this beautiful re-work. ;)
     
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  5. Leestereo

    Leestereo Super Member

    Messages:
    2,140
    Location:
    Ottawa, ON
    IIRC, the owner of this particular 555A doesn't post much, but he did send me this message afterwards: "Wow, l'm very impressed. Tons of power, excellent from top to bottom with a silky clarity. And an awesome phono stage as promised."
     
    Hyperion likes this.
  6. savatage1973

    savatage1973 Addicted Member

    Messages:
    6,361
    Location:
    NW Pennsylvania snow belt
    Nice work! What "dunce" thought that it was a good idea to "suffocate" resistors inside a piece of plastic tubing? :crazy:
     

     

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  7. slimecity

    slimecity Super Member

    Messages:
    3,069
    Location:
    New Zealand
    Thats how sansui did the originals - presumably to insulate the leads. Not sure how much heat comes off these resistors.
     
  8. sansui 74

    sansui 74 Active Member

    Messages:
    118
    Location:
    Seattle Wash
    Nice work,are those Mylar caps ? I see In the photos ,so how much difference do they make in sound quality. Ken
     
  9. Leestereo

    Leestereo Super Member

    Messages:
    2,140
    Location:
    Ottawa, ON
    Ken: The signal path electrolytic capacitors were replaced with mylar (polyester) WIMA-brand stacked film types and the stock green mylar capacitors were upgraded to polypropylene film types or C0G types. IMO, the film capacitor upgrades do noticeably improve the sound, but equally important are the Baxandall Diode and the Vbe Multiplier capacitor mods (click here for more detail on these).
     

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