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Sansui AU-D7

Discussion in 'Exclusively Sansui' started by gpounce32768, Jun 15, 2017.

  1. gpounce32768

    gpounce32768 AK Subscriber Subscriber

    Messages:
    322
    Location:
    Baltimore, MD USA
    I've been wanting to try out fixing up a Sansui for some time, I finally came across one that I liked; missing volume knob, amplifier issues, dead lamps... perfect!

    I'll make a new knob in the shop, no sweat. Inside its a little dirty but the left channel has different driver transistors and some scorch marks on the board so definitely some trouble buried in there. The amp circuit is a lot fancier than other units I've worked on, and the absurdly high damping factor of this unit (200) caught my eye.. so we'll see how it goes as I dig in.

    1st step is to give the unit a bath & deox the controls. Then evaluate the amp section, check out the damage and see about getting spec power transistors for the right channel- or appropriate upgrades for both channels. As I go in, I'll check capacitors etc and if any are sketchy or have drifted particularly then I'll recap the set.


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    Last edited: Jun 16, 2017
  2. leesonic

    leesonic Hold on, here comes the bass. Subscriber

    Messages:
    5,394
    Location:
    Southern NJ
    That I've gotta see!

    :lurk:

    Lee.
     
  3. woofmytweets

    woofmytweets AK Subscriber Subscriber

    Messages:
    1,230
    Location:
    Toronto, Canada
    looks like your power transformer sustained a direct hit. i hope it can still transform
     
  4. gpounce32768

    gpounce32768 AK Subscriber Subscriber

    Messages:
    322
    Location:
    Baltimore, MD USA
    Short of the armature being crushed or broken not much to is going to hurt a transformer unless the coil is damaged.... I suppose the case got banged around a bit- whatevs I'm not into it for the looks. Seller reports the unit powers up. Knob will be aluminum, I'll try out a different # of flats on it than I did for the Kenwood I did previously, not concerned about making it look completely original. Maybe I'll try color anodizing so it sort of matches colorwise.
     
  5. LBPete

    LBPete Rolling Along Subscriber

    Messages:
    10,337
    Location:
    Long Beach, CA
    Nice Amp. Please post the serial number for the database. Click on the link in my signature block.

    - Pete
     
  6. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
    2,173
    Location:
    Mississippi
  7. gpounce32768

    gpounce32768 AK Subscriber Subscriber

    Messages:
    322
    Location:
    Baltimore, MD USA
    Left channel damage.. looks dramatic :) the little board with the 6 thermal compensation resistors isn't burned as far as I can see - its smoke from the burned up resistors. Going to clean all the crud off and use silpads instead, I really don't care much for micas and thermal paste. The board layout and mounting is not very convenient for servicing either.. kind of a nuisance to work on this amp.


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  8. gpounce32768

    gpounce32768 AK Subscriber Subscriber

    Messages:
    322
    Location:
    Baltimore, MD USA
    The left channel is a shambles. .33 ohm double emitter follower resistor open on one side, drifted on the other. The intermediate driver follower resistors also all burned, one of the larger ones got so hot the leads torched out the thru holes and half melted the 33pf styrene feedback cap. My guess is this is a botched repair that cooked things even worse than the initial failure. As found, a .22 ohm emitter follower was tacked onto the foil side of the board, connecting the open half of the double emitter resistor- perhaps that was the original failure.

    Replacing all the dead resistors with 1% metal films, 1% modern film cap for the feedback- and will replace the same on the right for symmetry. Replacing all 4 driver transistors, putting in FJA4310/FJA4210 instead of 2SC2581/2SA1106. We'll see if any of the other intermediate driver transistors are blown later on when I do the dim-bulb powerup.

    The case splits into front/rear halves. If the rear half is detached to make room for the speaker output board to move around, and the audio input cable unsoldered from the amp board it can be more convieniently serviced.
     
    Last edited: Jun 19, 2017

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