Sansui 3000 main caps wired in backwards from factory

Discussion in 'Exclusively Sansui' started by kwayde, Feb 6, 2018.

  1. tom3

    tom3 Super Member

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    Could be wrong, probably. But those old Sansuis had a plus and minus power supplies for the amps, gets rid of the pnp/npn combination of transistors back there. Could be those caps are right for the actual polarity of the circuit?
     

     

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  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I just checked the schematic, it has 2 x +/-40V rails, made up of:- 2 transformer secondaries, a bridge for each channel, and a pair of main smoothing capacitors on each bridge to derive the +/-40V, I can't understand why there is confusion here. :)

    There are 2 x NPN OP transistors per channel, and it is unusual to see +/- rails with this combination, but this is no ordinary amplifier as it has transformer coupling in the OP stage.
     
  3. kwayde

    kwayde New Member

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    The silk screening is the same for all four caps. [​IMG] [​IMG] C12 was the only one installed with the negative post towards the inside of the unit, or towards the top in the pics.. Before I started working I took pics of them as a back up. The 2 caps were wired backwards, and they did not explode or vent. All of them have started to fail which can be seen by tiny dimples on the bottoms.

    The first pic pic shows C12 on the right with it's negative post towards the top. C11 , C10, and C09 are put in reversed of C12 with the negative towards the bottom. Second pic is C10 (top) and C09.

    It's hard to see, but the blue lead from the transformer is connected to the top (neg) lead of C12 in the first pic, which is incorrect. There is the blue lead and a black lead that connects to the positive lead of C11, which is incorrect. In the second pic, the yellow lead from the transformer is connected to the positive lead of C10, which is correct. The first pic caps are wired backwards, the second pic caps are wired correctly.
    [​IMG]
    [​IMG]
     
    Last edited: Feb 8, 2018
  4. kwayde

    kwayde New Member

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    Go back and look at the pics I posted with explanations.
     
  5. kwayde

    kwayde New Member

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    Had a little time. I put the cap back the way the factory had it wired. Took voltages:
    -35v on C11 neg post.
    +35v on C12 pos post.

    They should be:
    -v on C12 neg post
    +v on C11 pos post

    C09 and C10 are correct:
    +35v on C09 pos post
    -35v on C10 neg post

    I should be able to wire C11 & C12 similar to C09 & C10 to get the circuit right.
     
  6. sregor

    sregor AK Subscriber Subscriber

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    Um - looks like the reversed the polarity, and the wiring. Usually - on the negative and + on the positive with grounds on the other posts will work....
     

     

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  7. kwayde

    kwayde New Member

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    I switched C12 & C11 around to be wired the same as C09 & C10 and was going to check voltages. As soon as I powered it up I heard sizzle. Shut it down right away and felt C11 & C12, which were very hot. I'm going to wire new caps in their place, but in the way they came from the factory. Not going to worry about it anymore.
     
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  8. petehall347

    petehall347 the brandy coffee man Subscriber

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    so we all told you what would happen then you go and do it anyway .. one way to learn i suppose ... :idea:
     
  9. Robisme

    Robisme Sansui Enthusiast Subscriber

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    Um, yup.

    Rob
     
  10. DougBrewster

    DougBrewster AK Subscriber Subscriber

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    Full marks for coming clean..
     
  11. tom3

    tom3 Super Member

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    .
    Yeah, I've never done anything like that.....
     
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  12. kwayde

    kwayde New Member

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    Figured it would happen....but the curiosity got the better of me. Just couldn't let it go.
     
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  13. kwayde

    kwayde New Member

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    Well, my friend may get a little upset. After replacing a couple dozen caps the FM sounds tinny like it did before I started on it. I hooked up a cdp to the Aux. which has much better tone, but now I can hear the right channel is distorted. The unit has problems that needs addressing, but I'm not sure if he's going to invest anymore money into it.
    The first receiver I ever bought was a Sansui 3000A used. I was just a kid. Mine would go into protection mode often which angered me. The schematic came with it, so being the curious one, I found the circuit, opened it up and tweaked a coil. It never went into protection mode again. Probably wasn't protecting anymore either.
     
  14. stereoguy70

    stereoguy70 AK Subscriber Subscriber

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    So, you replaced the main filter caps, which had clearly failed, and the sound is the same as before. :idea: Did you bother to replace the rest of the electrolytics in the unit or just those four? Chances are the rest of the caps in the unit are shot too as they were the same age as the four you replaced.......I wouldn't be surprised if you did some damage to some of the transistors by trying to "fix" the "factory's mistake" as you put it as well. o_O
     
    Last edited: Feb 12, 2018
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  15. slimecity

    slimecity Super Member

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    Yup - meaning they were subject to reverse voltage and any longer coulda gone boom.
     
  16. dr*audio

    dr*audio Fish fingers and custard!

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    The electrolytics in the tuner tend to go bad in this model. Probably the reason for the tinny sound.
     
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  17. Bob

    Bob AK Subscriber Subscriber

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    throughout AK, there have been lots (hundreds if not thousands) of posts regarding
    schematic errors, part layout errors, board stenciling errors, and component errors
    (like some of the AK giants have noted parts like caps with voltage ratings barely
    above the circuit's, and components with voltages supplied above the max, etc).
    so perhaps, do a search against the manufacturer and/or the unit and/or
    similar units and/or any recap/refresh/rebuild threads.

    as others have also noted, mark the cap's polarity on the board. Using
    nail polish, magic marker, fluorescent highlighter, oil/latex paint, beer, etc
    (takes less than 5 minutes - and perhaps saving the unit)

    and before making ANY circuit changing decision, decide/ask/test whether
    the unit worked before with the existing/untouched parts/board-layout/schematic.

    then as a safety precaution, use NON-polar or BI-polar caps. then you can wire
    it in willy-nilly. do the board polarity marking and leave it in for the next guy
    in case you decide it's not worth the effort, etc. and he decides to undo your efforts.
    Use the green Nichicon Muse ES caps for color-coded street creds and audio bragging rights.

    and if you are truly anal-or-genius then compare actual board with parts layout diagram
    with schematic with parts list - all must agree AND mark the caps polarity on top of
    board and bottom of board and any changes (ceramic, polarized, tantalum, NP/BP,
    film, Teflon, organic polymer, etc) you deem mandatory.

    then lastly to prove said-genius, document one or all three of the above with
    two colors, green for replaced equivalent and red for upgraded/re-engineered
    with values noted. mark the component if you are thorough (10 seconds each MAX)

    or do what the AK giants do: take pics and describe changes. this will also help
    others with the next fix.

    I'm a full subscriber to the theory: "not always right, BUT never in doubt"

    when it's all done, then really enjoy the music.
     
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  18. mars_volta

    mars_volta Super Member

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    Negative side of the supply = backwards caps iirc
     
  19. kwayde

    kwayde New Member

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    I replaced more than a couple dozen electrolytics. The unit sounds exactly as it did before the change. Also found the muting switch has no effect whatsoever.
    My friend loves the Sansui sound and has many pieces. I have a Sansui AU7500 amp that I'll be using in the garage once I get settled in.
     
    Last edited: Feb 13, 2018
  20. stereoguy70

    stereoguy70 AK Subscriber Subscriber

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    See below.....
     

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