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Sansui 800 - Rebuild

Discussion in 'Exclusively Sansui' started by Super Noob, Apr 2, 2017.

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  1. Super Noob

    Super Noob New Member

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    Have just started replacing caps on this 800.

    The power amp boards have new caps and transistors (KSC1845) two each.

    Also replaced the axial caps on the bottom of the unit and the large radial caps (4) as well.

    When I plug it in, the transformer hums and the power transistors get really hot - fast.

    I am thing about redoing the cap mounting around the transformer. Checked that nothing is in backwards - 2x.

    Was hoping for good result.

    Anyways - struggling through.

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  2. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Have you checked if the voltage is correct??? Maybe you switched it to 220v or something??
     
  3. Super Noob

    Super Noob New Member

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    I am perplexed... need to sharpen my trouble shooting skills. The switch has not moved = 110V (AC).

    Something is not right... but I have checked everything numerous times. Thanks for the suggestion.
     
  4. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Try putting back the old transistors that you replaced with KSC1845 - only do this if you are absolutely SURE you know which way round they went.

    Note that it is very common for previous trimmer settings (for bias and DC offset) to be a long way out after component replacements - especially if you have changed transistors. Best to make sure the bias trimmers are turned so that bias is at a minimum BE CAREFUL - easy to get this wrong and turn them to maximum with a very bad outcome if you do this.

    The best way is to monitor the bias current and turn the trimmer carefully so the bias reduces - then you know which way to turn them. (make a note of where they were set in case it all goes pear shaped).

    Your receiver is in a very precarious state - one slip, or leaving the unit on too long with those transistors heating up as you describe, and you will have a disaster on your hands. Before doing any of the above it might be a good idea to check your work again, with the unit powered off of course.

    I have never seen an 800 - as vintage receivers are rare over here, someone who has seen/worked on one would be best to advise you further.
     
    Last edited: Apr 6, 2017
  5. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    You have a dim bulb tester right?
     
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  6. stereofun

    stereofun AK Subscriber Subscriber

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    You might have done everything right in terms of getting pin outs, polarity etc. What could happen, especially with transitior replacement in tight spacing, is that a joint is making contact with a neighboring trace when it shouldn't.

    So re-checking your work really is the solder work as well. If you have a good side / bad side, you might be able to swap driver boards and see if "hot" side changes. This could isolate the culprit to one driver board, making it easier to troubleshoot by comparing continuity / dis-continuity of traces and joints.

    As Hyperion suggest, you really want to make sure the bias pots are turned down on both sides first.
     
    Last edited: Apr 6, 2017
  7. Super Noob

    Super Noob New Member

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    Yes... I suspect a poor solder job. This amp has capacitor coupled output. Have not touch the bias pots. Agreed that I need to go through the board and get some reading.

    Will hopefully get back on it tomorrow. Thanks for the good comments - much appreciated. Everything is in the boards right so I must have leakage across joints.
     
  8. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    The bias will be affected by the new components, check the manual and back them off as far as they will go...
     
  9. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    A safe way to determine which way the pot goes ( cw/ ccw ) is to hook up your meter to the pot and set it to ohms. As you adjust it with the unit unplugged, you will see your meter display which direction the resistance is going... they are not always counterclockwise.....
     
  10. KingBubba

    KingBubba "Too Much Stuff" Subscriber

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    Regardless of what might be said in the service manual, always check the pots the way the Fuxtor described. When I first got my Sansui G-8000 I read the instructions on setting DC offset. It said to turn the pot all the ways counter-clockwise. Before I did that, I checked with the meter. It turned out the pot was backwards from the type of pot that was supposed to be in there. If I had set it counter-clockwise, it could have been a mess. When I had it rehabbed I had Bourne pots put in. Much more better.
     
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  11. Super Noob

    Super Noob New Member

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    Well, I found the problem. Needless to say my inexperience was the factor.

    CDC8002 and CDC9002 originally with replaced KSC1845. With the 9002 being a PNP.... not good. Anyways decided to get new KSC2690A and KSA1220A (compliments)

    I also changed out the other two transistors on the driver amp boards (cans). Recapped the EQ board and replaced all the 2SC458 with KSC1845s.

    Anyways... my first rebuild is done. $15 purchase + $40 parts = hours of research and component swapping was enjoyable.

    Adjusted the output to 27VDC on both boards on the lesser output transformer (collectors) and the higher output collectors are ~54VDC.

    Have some equipment I like = Realistic STA2100, Sansui G-7500, Yamaha ASP-A1, Marantz TA170AV and others. This Sunsui 800 just sounds amazing at 28 WPC. It is pushing my OHM Model C. Never thought it would be this good.

    Thanks to Fuxtor and others for helping.

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  12. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Hey.... Alright! Good for you! It always feels good listening to a unit after you win the battle!!
     
  13. Super Noob

    Super Noob New Member

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    [​IMG]

    Bone Yard.
     
  14. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Once all the components get a few hours thru them, I bet you will be pleasantly surprised at the sound quality of that unit...
     
  15. Super Noob

    Super Noob New Member

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    SX-850 rebuilt + Sansui 800 rebuilt = many smiles.

    This little unit is a keeper and sounds amazing / sweet = the reviews are right.

    Now working on a Citation 16A = should be fun if I can breath life into this monster.

    OLA are in the process of being resurrected.

    Not an audiophile snob = but I know what sounds clean.

    Or maybe the rescued orphans are held in higher regard = no way.
     
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  16. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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