Recapped Sansui AU-719 Protection mode help!

Discussion in 'Exclusively Sansui' started by RR--, Mar 3, 2017.

  1. RR--

    RR-- Active Member

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    217
    Location:
    Melbourne, Australia
    I think we've fixed the burning! All I did was replace TR610, TR611 and TR612 and clean up some solder joints and no burning! Listening to music now and it's sounding sweet again.
    I could barely even tell at the time but I think the problem was a very small short between the solder joints on TR610 and TR611, weird it only became an issue after I had worked on the driver boards, that threw me off.

    I'll order a new capacitor for the phono board (I currently have the 1979 original installed) and those two zener diodes you recommend Hipocrates.

    Thanks heaps for the very detailed advice, now it's time to give this a good long listen to see if the protection issue is still there, I'll keep you all updated. :music:
     
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  2. Hipocrates

    Hipocrates Anti-Muppet

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    It is a good practice to clean the work done, as we can see... Sometimes can be a tiny blob of solder or a tiny piece of wire, and that can become a tricky issue to diagnostic.
    Now let's see how it goes. Good work!
     
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  3. RR--

    RR-- Active Member

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    Thanks! I usually do on other boards but this power supply board is a huge mess to remove so I've been doing most of the work with it still in the amplifier which could be the problem.
    Also it was strange, when soldering on the AU719 board it tends to melt and bubble slightly where on my 8080 it was fairly clean. Maybe it's just dirtier or a less robust PCB?
     
  4. Hipocrates

    Hipocrates Anti-Muppet

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    maybe some old flux? I couldn't say... Sadly I have never seen an AU-719 in person.
     
  5. RR--

    RR-- Active Member

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    Melbourne, Australia
    I've been using it daily since 2013 and I love it, it has probably the best volume dial I've used, it's an ALPS pot and very smooth with a tactile bumps the whole way. My 8080 sure is giving it a run for it's money in terms of soundstage though.
     
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  6. RR--

    RR-- Active Member

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    Hey another request, do you know of an alternative zener diode that's equally as good available on RS Components? I checked and two you linked to are again only available in quantities of 200. :crazy:
    Mouser shipping is only free above $60 so for individual parts RS is much cheaper for me.
    Thanks

    https://au.rs-online.com/web/p/zener-diodes/8128721/
     

     

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  7. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I don't see the correct part on that website that's available in small quantities - the one in your link above is wrong - as it is 1.3W - far too much power.

    You want 400 or 500mW 6.2V, 2% or 5% ;) (actually 5% will be fine here for ZD601 as the zener in this position is not used for its voltage accuracy).

    This is the cheapest option if you don't mind spending $10 for a few (99) spares. :rolleyes:

    https://au.rs-online.com/web/p/zener-diodes/0509093/
     
    Last edited: Jun 13, 2018
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  8. RR--

    RR-- Active Member

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    Shows what I know about zener diodes haha.
    In your opinion (and Hipocrates of course) how important is it to change these Zener diodes? I'm thinking I might just leave it on my to do list until I buy something else from Mouser if it's not a big deal.

    Also small update on my AU719, after readjusting the Bias and DC it's sounding a lot better, it does have a new strange quirk though, it only starts on the second time every time.
    Like if I switch it on the protection light will blink forever, but if I turn it off then on again it will always turn on. It's really consistent too. I'm wondering if one of the replacement parts isn't an accurate enough replacement. I still have the original parts I could put back in if needed.
     
  9. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Not that important in my opinion, they really only need changing if they are actually faulty, however I like to change zeners in some positions a). in case they might have/will become, noisy with age, and b). they often get a bit warm, and as a voltage stability part I usually re-mount them up from the PCB just a little for air circulation - which means longer leads = replacement zener. I the case of ZD601 it is only used to speed up the action of turning on the relay driver transistor - and doesn't get hot, so none of the above applies.

    As for your 'second time lucky' fault - I'll need to think about that for a while.

    Question
    How long do you have to wait before power on #2 is not successful? - and what parts did you change for this fault to show itself for the first time?
     
    Last edited: Jun 16, 2018 at 6:51 AM
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  10. Hipocrates

    Hipocrates Anti-Muppet

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    Go with what John says, he's the real expert here. I just chime in if you guys are stuck :p .
    If you replaced the zeners with wrong values, can be possible that the relay is not engaging well?
     
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  11. RR--

    RR-- Active Member

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    Location:
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    I'm not sure as the original protection issue only became fixed after replacing the transistors on the right channel driver board, so I think it's safe to assume this new 2nd time lucky protection issue only came about when I replaced quite a few parts on the protection board.
    If I had to guess how long it would take to make the 2nd power on unsuccessful I'd say however long it takes for the amplifier to cool down enough, so far every morning it constantly takes two attempts, also I just had the problem occur in when having the amp off for less than 10 minutes, this is probably due to the fact it hadn't been used very loud. It's pretty cold at this time of year in this part of the world, although cold just means wear a jacket.
    I'll swap back in the original zener diodes if I can establish which ones go where when I have some time next and post an update. Other than that the original protection issue seems to Finally be fixed. :banana:
     
    Last edited: Jun 16, 2018 at 9:02 PM

     

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  12. RR--

    RR-- Active Member

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    Update
    I replaced the zener diodes with the originals (With some added height for good measure) and everything seems very much the same including the 2nd time the charm protection issue, I decided to swap back in the original SCR and now the amplifier powers on first time every time. I think the larger replacement SCR was a little too large although a previous commenter had success on their AU-519.
    All in all I think this amplifier is all fixed (knock on wood) I still have to replace the Bias trimmer pots and a capacitor on the Phono board, I do like with all these new transistors the amplifier is very very quiet when not playing any music.
     
  13. RR--

    RR-- Active Member

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    217
    Location:
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    Aaaand I'm pretty sure I just jinxed it, a new problem just started, after listening to some music the right channel began cutting in and out, after playing with all the knobs it plays music but quietly. When not playing music that channel hisses quietly. Well it was a nice 30 minutes or so I guess. :bs:
     
  14. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Quick test, invert the two input molex connectors to those driver cards and see if the issue changes sides.
    Second test, with unit off cycle the separated connected switch a whole bunch of times and see if that fixes it
    As a side note, that *%(*&&*() protection circuit can be the most (&^%)(*_) contrary circuit of anything Sansui ever designed, when it wants to mis behave it can and will drive folks crazy.
    Don't ask me how I know that :biggrin:
    -Lee
     
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  15. skippy124

    skippy124 Super Member

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    Hi Lee,

    The 719 doesn't have the connected/separated switch, it was removed from this version. And agree with your thoughts on the protection circuit, been there done that too ..........

    Cheers

    John
     
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  16. RR--

    RR-- Active Member

    Messages:
    217
    Location:
    Melbourne, Australia
    Thanks for the suggestions Overundr I'll give it a try, my amplifier doesn't have a connected/separated switch, so far I have flushed out all pots (excluding the sealed volume pot) but it made no difference. I can confirm this amplifier has pressed a few of my crazy buttons already haha.

    Just to confirm so I don't accidentally break anything, which connectors should I swap? I have colour coded my plugs as to avoid making any mistakes in the past.

    [​IMG]
     

     

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