Sansui 3000 main caps wired in backwards from factory

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

  1. kwayde

    kwayde New Member

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    I'm in the process of changing the electrolytic caps in my friend's Sansui 3000. I'm changing out the main caps, C09, C10, C11, & C12 first. I pull C12 first, replace it exactly how it was wired up from the factory, then check the schematic to be sure it's correct. Turns out the receiver has C11 & C12 wired in backwards according to the schematic. I checked C09 & C10 to see about them, and they're in correctly. Having a hard time understanding how the factory could let something like this slip through. I listened to the unit before I started any work on it, and the unit seemed to be fine, other than it sounding tinny with a lack of bass.

    Anybody else come across anything like this? Don't know whether to leave it as is, or wire them up according to the schematic.

    https://www.hifiengine.com/manual_library/sansui/3000.shtml
     
    Last edited: Feb 6, 2018

     

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  2. petehall347

    petehall347 the brandy coffee man Subscriber

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    they would have blown the main fuse in backwards .
     
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  3. Robisme

    Robisme Sansui Enthusiast Subscriber

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    Put them back in the way you found them. Sansui service manuals and schematics have been known to have mistakes in them from time to time.:D

    Rob
     
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  4. petehall347

    petehall347 the brandy coffee man Subscriber

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    hi-fi engine schematic shows them correct way around ..just look where they connect to bridge rectifiers
     
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  5. sregor

    sregor AK Subscriber Subscriber

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    I would bring it up slowly on a variac, and make sure the + and - voltages are correct. )I'm surprised they haven't gone, and would be very leery of firing it up full power until I have a better feel for what's happening.) My 2 cents....
     
  6. kwayde

    kwayde New Member

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    Nope, didn't happen. Fuses are good.
     

     

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  7. kwayde

    kwayde New Member

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    The schematic shows them in correct, but C11 & C12 are wired in backwards. The blue lead from the transformer is soldered to the negative lead on C12. On the neighboring bridge, the yellow lead from the transformer is soldered to the positive lead of C10. All of the leads are on the wrong terminals on C12 & C11.
     
  8. kwayde

    kwayde New Member

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    Don't have a variac. I turned it on to listen to it before I started to work on it to get an idea of how it sounded. Other than it sounding tinny with a lack of bass, I really didn't pay much attention to anything else. Since the identical circuit next to it is wired correctly, I'm thinking I should wire up the one that is wired wrong correctly to see what happens. Will have to check with my friend when I see him tomorrow to see how he feels about this since it belongs to him.
     
  9. kwayde

    kwayde New Member

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    I thought about doing that, but it just gets on my nerves. The circuit next to it is identical and the caps are all wired correctly, so I'm thinking this circuit should be wired the same. I have someone else looking at this too. Haven't heard from him yet.
     
  10. restorer-john

    restorer-john Addicted Member

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    It's more likely that the silk screening on the two caps is back to front and the has thrown you. The caps would definitely have vented and exploded decades ago if they were indeed wired incorrectly.

    Also, check out the service bulletin for that unit- 1000uF non-polar caps on the output.
     
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  11. kwayde

    kwayde New Member

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    What are the odds that two improperly silk screened caps would end up next to one another in the same circuit, same amp? Also, the owner doesn't want to put a lot of money into this, so instead of doing the service bulletin fix I just fused the speakers.
     
    Last edited: Feb 7, 2018

     

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  12. petehall347

    petehall347 the brandy coffee man Subscriber

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    pcb silk screening is often wrong
     
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  13. sregor

    sregor AK Subscriber Subscriber

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    Quick check - One of the collectors of the output transistors goes directly to the + supply Through fuse), and can be easily verified with your meter. The emitter of the other one on that channel connects to the - supply through a low (less than 1/2 ohm) resistor (also through a fuse) and can be checked, but not as easily. (but not that hard)
     
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  14. kwayde

    kwayde New Member

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    These caps are not mounted on a pcb.
     
    Last edited: Feb 7, 2018
  15. kwayde

    kwayde New Member

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  16. kwayde

    kwayde New Member

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    What I've decided to do is to connect the new cap the way the bad one was installed, which is backwards. Then I'm going to check voltages. I may possibly have time tomorrow to do this.
     

     

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  17. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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  18. Dave_1962

    Dave_1962 Lunatic Member

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  19. Hyperion

    Hyperion Roobarb & Custard Subscriber

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  20. dr*audio

    dr*audio Fish fingers and custard!

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    Put the original caps back in wired as you found them, THEN take your voltage readings. If you get this wrong with the new caps you will destroy them. Quickly.
     
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