AU 5900 recap

Discussion in 'Exclusively Sansui' started by Dearslayer, Jan 9, 2019.

  1. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    this unit is working and has been sitting on my shelf for about two years now. Got a good deal on it from a friend. I've recapped a few Marantz units but never a Sansui. Started to run out of things to recap so I thought it might be time to give this one a try. I just put it on the bench to remove the top and bottom covers off to have a look. I want to take inventory of the caps to see what I might need to order. I still have a little to finish on my Marantz 112 Tuner and need some parts so I can order everything at once. Wow I don't know where to even start to get at these boards or pull this thing apart. Is it as hard as it looks. Any pointers or photos showing the process? Anyone possibly have a cap list for the 5900. Any recommendations on how to proceed and what to watch out for?

    GT.
     
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  2. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    Well I went ahead and took the PS board out of this unit. It wasn't as difficult as it first appeared. Just not familiar with Sansui I guess. Making a list of Cap values etc so I can place an order with Digi-Key. Would there be any troublesome transistors that I should be replacing so I can include them in my order? Also are there any diodes that should be replaced such as the little red blobs circled in the photos. Thanks.

    GT.
     

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  3. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    Nobody??
     
  4. slimecity

    slimecity Super Member

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    Go thru each board by sight and note down the cap values - you want to note what is fitted tot he boards rather than what the SM says.

    Get the service manual and identify the little blob diodes. They dont look like VD1212 diodes to me based on a quick glance (more like MV-03 types), if they arent VD1212, just leave them in there.

    I can see a 5-pin transistor thats probably on the input stage of your power amplifier. You would be better off preventatively replacing that. It is probably a "2SA" something. If so, each one can be replaced with 2 x KSA992's matched in hFe and heat-shrinked together
     
  5. spark1

    spark1 Super Member

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    Yes, replace VD1212 diodes with two 1N4148 diodes in series I think there are four of them in there, but as said above refer to the manual. You may also want to replace the fuse resistors and reseat the output transistors with new mica insulators and thermal compound. Be aware that Sansui usually bent over the legs of the components, which you may have to pry a bit when desoldering. Be slow and steady....you don't want to lift the solder pads. On the 7900 and 4900 I did, I still ended up having to bridge a few. Can't think of anything else offhand, but it's been a while since I did them. See the service manual for removing the main board from the heat sink.

    EDIT: I do seem to remember a few BP/non-polarized caps that are not noted as such in the service manual. So, as always, it is a good idea to build your order by looking at the boards. And now that I actually looked at the pics, it seems like you have indeed located the VD1212s (and already pulled the main board...which seems like it would be difficult but as you have found, is actually not). I found the preamp board the most challenging to get to, and even it was not bad at all.

    And now that I read slimecity's post, I do remember replacing the dual transistors, just as he said. They have a reputation for going bad.
     
    Last edited by a moderator: Jan 30, 2019
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  6. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    Thanks so much for the replies. I was beginning to feel abandoned. :dunno:Lol.
    I’ve already took inventory of the boards and wrote everything down just to be safe and I’ll be placing a parts order in the next couple days with Digi-key once I confirm everything. I did read in another thread about that 5 pin transistor and I’ve replaced the differential pairs in various Marantz units in the past, but how does one go about using two 3 legged transistors in a 5 pin out, location ? I had planned to replace the low value uF caps with Wima Film caps, ( also on the order ) especially on the tone board. Looking at that tone board it looks as if the front of the unit might have to be removed to access no? I have only taken the PS board out thus far to take inventory. Never worked on a Sansui before so this will be a learning curve.
    G.T
     

     

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  7. spark1

    spark1 Super Member

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    If I remember correctly, I did indeed have to remove the inner front panel on the 7900 to get at the sandwiched boards of that unit...but it seems like I could just pull the single board of the 4900 by removing the nuts on the pot shafts and the mounting screws of the switches. Don't know if the 5900 is like the 4900 or the 7900. I'm sure someone will provide more useful info soon.

    As for the 2SA798s...two KSA992s, installed with emitters in the middle hole, and then heatshrunk together (or small zip tie) for thermal consistency. Ideally, you would match them, but I donj't think there is much variance in modern transistors anyway. Put a thin layer of thermal compound on the facing surfaces to better assure same temp on both devices.. You may need to expand the middle hole just a bit...I just ream it with a thumbtack, but drilling is probably more elegant.
     
  8. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    Awesome....I'm sure that once I get to those transistors in the coming days, I'll be asking for more confirmation.
     
  9. spark1

    spark1 Super Member

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  10. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    Excellent info Spark1 thanks so much.
     
  11. spark1

    spark1 Super Member

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    You are most welcome. Let us know how it goes.
     

     

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  12. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    I started to replace a couple caps tonight before leaving for work, that I had on hand ,while waiting for my Digi-Key order. I think normally it's ok to replace small uF values such as 50V 1uF Polar with Wima Film 50V 1uF. I did this for the one circled in top left of the photo. Hope that's ok.
    I also noticed that the one circled in the bottom right of the photo was a 6.3 100uF BP. I missed the fact that it was a BP cap the first time round ,so I had to cancel my order and add this cap and re-order. It will be another day later now for parts. Damn.

    edit...also increased that 6.3V BP to a 16V.
     

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  13. spark1

    spark1 Super Member

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    I mentioned that in my earlier post, in the hopes that you would catch it.

    Yes, I use films up to 3.3uf, if space allows.
     
  14. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    I do remember you saying that so..... I'm gonna put it down to this damn night shift making my brain foggy. Been doing this shift work for way too many years....near on 30 .
     
  15. SansuiJavier

    SansuiJavier AK Subscriber Subscriber

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    Following this thread because I have intermittent fault in my 6900. Suddenly makes pop and crack noises in both channels and reaches protection. Spend days without doing it. I have it with the lid removed and running, waiting and it does not. It's crazy ... I want to do a recap but I can not find the intermittent fault. Can the 2SA798 cause this failure?
     
  16. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yes it could - but I would think only in the channel where the faulty 2SA798 is located - both channels affected suggests a PSU fault.

    Well done for holding off with the recap until you can get the unit working properly, this is the correct way to deal with your unit. :thumbsup:

    Have you tried careful application of 'freeze spray' - and gentle tapping (with the blunt end of a screwdriver) and lastly my favourite, gently nudging each small signal transistor with a non-conductive probe in two different directions. I am assuming here that you have closely visually inspected all likely solder joints, and remade any that look suspicious, checking for things like cracks, blowholes, de-wetting, excessively blobby joints possibly hiding dry joints underneath and so on...

    Apologies to the OP for what might be considered a thread crap.
     
    Last edited: Jan 23, 2019
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  17. slimecity

    slimecity Super Member

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    This may be occurring as once the lid is removed, the problem component does not get to warm enough to get into a fault state. Taking off the lid makes a very big difference to component temperature.
     
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  18. Dearslayer

    Dearslayer AK Subscriber Subscriber

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    About to do the tone PCB and realized I don’t have the two Wima caps to replace the two 50V 2.2 uF electrolytic caps that are currently at C11 and C12. I do however have 50V 3.3 uF Wima. I know it’s not common practice to increase the uF value in most cases however I think occasionally depending on its placement in a circuit it’s sometimes done. I do have 50V 2.2 in a electrolytic cap. So should I replace with Electrolytic at the same value or increase to 3.3 and use the Wima?
     

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  19. p4spooky

    p4spooky New Member

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    The orange caps are low leakage as you know. If you have Nichicon KL (2.2uF) then go ahead and replace. my recommendation is avoid changing capacitance in tone control circuits.
     
  20. spark1

    spark1 Super Member

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    I think most, if not all, of the Nichicon "audio grade" caps fall into the low leakage category. I second the recommendation for maintaining same capacitance.
     

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