G5500: low output & distortion RH channel

Discussion in 'Exclusively Sansui' started by Pageplayer, Feb 9, 2019.

  1. Pageplayer

    Pageplayer AK Subscriber Subscriber

    Messages:
    163
    Originally had blown outputs on right channel. Someone had already repaired or attempted a repair at one time judging from broken traces and pads on the 2981 board.
    I replaced output transistors on both channels, all emitter resistors, driver transistors, all VR's with Bourns units and almost all caps on the F-2980 board. (after removing tons of dried glue!)
    Still have low output and distortion on the right channel. Left channel sounds great.

    I can adjust DC offset and bias on the left channel, but when putting the meter across R-channel emitters per manual I get 0v and adjusting VR04 does nothing.

    I'm perplexed that I have sound but no voltage across those emitters.
    G-5500 adjustments.gif
     

     

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  2. kevzep

    kevzep Its all about the Music Subscriber

    R35 and R39 on the F2980 are supposed to be 150Ω, check those. They are fusibles and drift with age and stress.
     
  3. Pageplayer

    Pageplayer AK Subscriber Subscriber

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    163
    Kevzep! Awesome..
    Are R35 and R39 for left channel?
    At any rate, I pulled and and checked R35&36 and R39&40. All were in tolerance.
     
  4. kevzep

    kevzep Its all about the Music Subscriber

    Ah, okay, I would say what you will find is a resistor somewhere around the bias circuit out of tolerance, I actually has this very fault recently and it was one of those resistors I mentioned.

    You could have a look at R37 (10Ω) also R51 and R53 220Ω (driver emitter resistors) and of course the main output transistor emitter resistors 0.33Ω 5 watt...
     
  5. Pageplayer

    Pageplayer AK Subscriber Subscriber

    Messages:
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    I kinda glossed over it in the first post but during my initial inspection I found R52 & R54 were indeed open. I also replaced all driver transistors with 2690AYS's

    I will start pulling and checking all the other resistors in the am..
    Thank you very much for your valued input.
     
  6. kevzep

    kevzep Its all about the Music Subscriber

    Hang on, a KSC2690AYS is a NPN, there should be the complementary KSA1220 to go with that too and they are TO126 packages, but I am sure even on the G5500 that the drivers are TO220's and 2SD357/2SB257??

    Can you confirm what you have done there?
     

     

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  7. kevzep

    kevzep Its all about the Music Subscriber

    The TO126 transistors can be replaced with KSC2690 and KSC1220, the TO220's can be replaced with MJE15033/15032 (although they are 30mhz instead of 100mhz), they do work though and its really one of few options available.

    I believe there is a worldwide shortage of KSA1220 at the moment, Mouser has no stock at the moment...
     
  8. Pageplayer

    Pageplayer AK Subscriber Subscriber

    Messages:
    163
    Sorry you're right.. I have 2690's in TR15&16
    And 1220's in TR17&18
     
  9. kevzep

    kevzep Its all about the Music Subscriber

    Okay thats good, what about the drivers?
     
  10. Pageplayer

    Pageplayer AK Subscriber Subscriber

    Messages:
    163
    Which ones are drivers? I thought TR15 thru 18 where drivers
    I have a lot to learn.. I :whip:
     
  11. kevzep

    kevzep Its all about the Music Subscriber

    Yes they are and they are TO220 packages and should be MJE15033/15032 if you have replaced them, not KSC2690/KSA1220...
     

     

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  12. Pageplayer

    Pageplayer AK Subscriber Subscriber

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    So put MJE15033/15032 in TR15 thru 18..
    I do believe I may have just enough.
     
  13. kevzep

    kevzep Its all about the Music Subscriber

    Yes make sure you get the PNP and NPN in the right positions...
     
  14. Pageplayer

    Pageplayer AK Subscriber Subscriber

    Messages:
    163
    Ok.. Today I swapped out the 2690's and 1220's with MJE15032/15033's and checked all resistors above the PS section, comparing left channel with right channel readings.If something was funky I would pull a leg and check it again.
    The only discrepancy I found was with R60. It's a 2.2Ω but R60 was checking high at 6.7Ω.. The closest match I had was a 2.4Ω so I used that for trouble shooting. I also swapped out a couple more PS caps.

    Upon powering up the unit, I could tell immediately there was a improvement in the right channel. No more distortion!
    With both channels running equal soundwise, I figured i'd better check Bias again.
    But, right channel is still reading 0v with no change when adjusting VR04.. (I swapped R59 and R60 2.4Ω test resistor / no change)

    I also notice TR18 (MJE15033) gets really warm compared to the others.

    My back is tired from hunching over this thing all day. :confused:
     
    Last edited: Feb 11, 2019
  15. Pageplayer

    Pageplayer AK Subscriber Subscriber

    Messages:
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    Pulled output TR's just to check them out but tested good. :dunno:
     
  16. Pageplayer

    Pageplayer AK Subscriber Subscriber

    Messages:
    163
    I realize I'm A rookie and maybe bit off more than I could chew, but ya never really know what its gonna take to get 'em running, but since I've already put a bunch of time and components into this unit, I'd like to see it thru and get this baby running properly.

    Now that I've changed all but the two 33uf 50v caps on the 2980 board, the driver TR' s, questionable resistors, etc, I'm thinking about swapping out some of the other transistors, but I'm a little gun shy about picking out the replacements..
    Is this list accurate?
    https://audiokarma.org/forums/index.php?threads/once-more-sansui-transistor-substitutions.583009/

    Thanks for your time.
     
    Last edited: Feb 14, 2019

     

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  17. Pageplayer

    Pageplayer AK Subscriber Subscriber

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    As mentioned in my last post, I'm contemplating swapping some of the TO-92's
    But had suspicions about resistors found on the backside of the board, especially since they're not seen in other G5500 board pictures I've seen, so now I'm wondering if they are original...
    20190214_200348-1-1.jpg
    TR19 & 20 are 2sa992's just as the manual confirms. The resistor across emitter & base it is a 330Ω.
    R41 & R42 isn't called out in the manual but is a 27k on top and a 220k on the foil side.

    What are your thoughts for the resistor across the transistors?
     

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