Sansui AU-919 restoration/upgrade thread

Discussion in 'Exclusively Sansui' started by mattsd, Jul 3, 2018.

  1. mattsd

    mattsd AK Subscriber Subscriber

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    Yep, it's that time. Finally got a little bench time to start on the one recap job I've been eagerly anticipating for awhile. :banana: Note this thread will be a long term thread, as stuff comes in I'll have to set this aside from time to time. Original thread on how I got it is here: http://audiokarma.org/forums/index.php?threads/just-got-my-keeper-integrated.816045/

    We start with the flat amp board (F-2841). I will be mostly following what @Leestereo did with his 919 (kudos to him and his excellent work), but I am upgrading a few more components. This 919 is an early model, which means it has 5pF black flag caps at C15 and C16 along with C31-34.

    Front of the board before recap:

    [​IMG]

    Back of the board before:

    [​IMG]

    First problem I ran into is that darn Sansui glue. Thankfully this stuff has not started to break down and cause corrosion, so a big plus there. It is mostly in two places, the 100uF local decoupling caps along with the film bypasses for them and the output capacitors and their film bypass caps as well. I got the decoupling caps photographed before and after but forgot to take a before of the glue on the output caps. Oops. You can kind of see it in the full photo up top.

    Decoupling caps before:

    [​IMG]

    And after:

    [​IMG]

    I also replaced C27 and C29 and cleaned the glue there, the big after photo will show this. Here is the photo of the output caps after glue removal and replacement:

    [​IMG]

    That's all for now, found I didn't add the replacements for the 33uF caps that shunt ZD03 and 04 to the BOM. :oops: They're on the way, so I'll be able to continue soon.
     
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  2. spark1

    spark1 Super Member

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    Keep up the good work, and continue posting pics of the process. Good stuff.
     
  3. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I'll be following along, another experienced restorer's take on how to recondition one of these is always worth a look. :thumbsup:
     
    Last edited: Jul 4, 2018
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  4. _mano

    _mano Active Member

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    John, Full time Hobby ?
     
  5. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Not quite :D I do a lot of reading of technical posts, but not much posting. The workshop is closed until Winter - at least to outsiders, so that my own gear gets to see the bench for some fine tuning :)

    When someone the calibre of Matt gives an AU-919 a once over - especially one for himself - then I am very interested. ;)
     
    Last edited: Jul 4, 2018
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  6. cnyel1967

    cnyel1967 AK Subscriber Subscriber

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  7. mattsd

    mattsd AK Subscriber Subscriber

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    And the flat amp board is all done!

    [​IMG]

    Back side:

    [​IMG]

    Now we move into the Control Board (F-2846) which the flat amp plugs/is soldered into. Just two .33uF (C01 and C02) caps here for the subsonic high pass filter. I used Panasonic ECW .33uF polypropylenes for the replacements

    Before:

    [​IMG]

    After:

    [​IMG]

    Next, the Tone Control (F-2842) and Tone Selector (F-2843) boards. I kept to stock values, both boards have identical cap numbers and values. All the original caps are mylar/polyester. C01 and C02 are .12uF 100v, C03 and C04 are .24uF (replacements had to be .22uF), C05 and C06 are .015uF and C07 and C08 are .039uF. Replacements were Panasonic ECW, Wima FKP and Kemet/Rifa PHE426, caps were measured for lead spacing and matched accordingly. One very nice benefit was the new caps are much smaller than the originals, making them easier to fit and won't pick up as much hum and noise.

    F-2842 before:

    [​IMG]

    F-2843 before:

    [​IMG]

    F-2842 after:

    [​IMG]

    F-2843 after:

    [​IMG]

    That does it for the front of the amp, I now will be moving back to the EQ amp board next.
     
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  8. spark1

    spark1 Super Member

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    This is great.
     
  9. ghamilton

    ghamilton Super Member

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  10. mattsd

    mattsd AK Subscriber Subscriber

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    Here is the MM Head Amp Board (F-2835), this board has a lot of caps to change. Being this is an early unit, the output high pass filter caps C55-58 are 47uF rather than the 100uF seen in later versions. This forms a 23.5uF "bi-polar" cap. I replaced them with a single 47uF. The local decoupling caps C47-50 were also 220uF rather than the 330uF found in the later models.

    [​IMG]

    This had a lot of the dreaded glue securing the decoupling caps, thankfully this stuff had not started to break down and corrode everything.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    And after! In addition to the caps replaced in Lee's thread, I also replaced the decoupling bypass caps C51-54 along with C37, 38, C41 and C42. Wima MKP 10 and Panasonic ECW caps were used. Note that the bypass caps were .47uF in this model.

    [​IMG]

    Next post, we'll be recapping the power amp board!
     
    Last edited: Jul 29, 2018
  11. spark1

    spark1 Super Member

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    Beautiful work.
     

     

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  12. lbcgav

    lbcgav AK Subscriber Subscriber

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    Beautiful work. It looks like you're keeping the original trimmers on this board. Which of the trimmers do you plan on replacing on this amp?
     
  13. ghamilton

    ghamilton Super Member

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  14. mattsd

    mattsd AK Subscriber Subscriber

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    I left the originals on there because I forgot to add them to the list. I have all the others though.
     
  15. mattsd

    mattsd AK Subscriber Subscriber

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    And here is the power amp board! Some differences noted between this and the later production runs, C01-04 were 220uF 63v rather than 470uF 63v. C19, C20, C45 and C46 were 10uF rather than 3.3uF. Also, C07, C08, C13 and C14 were 1uF on this one, as opposed to the 4.7uF of the later runs.

    [​IMG]

    And after! Everything was pretty straight forward, the big caps had some glue that needed removed and a few solder joints needed touched up, but other than that everything was out/in.

    [​IMG]

    Next post, the power supply board!
     
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  16. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    Nice!, appreciate the nice resolution!
    Great work!
     

     

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