Sansui 9090DB "The Basket Case"

Discussion in 'Exclusively Sansui' started by RuairiMutt, Oct 9, 2017.

  1. RuairiMutt

    RuairiMutt Member

    Messages:
    54
    Location:
    Lake Geneva, Wisconsin
    I barely know where to start with this poor pathetic thing.

    Let's start this with: I have it in for repair, and I made a massive, epic mistake; I started working on it when I was very tired and in a bad mood.

    It had cheap Chinese knock-off Toshiba outputs installed on the right channel. Fine, I pull them off and swap them, and in my not paying attention state, instead of installing the complementary pair, I installed four MJ21194G transistors and turned it on.

    POP goes half the 10 amp fuses.

    Step away, this was the crown on an already rotten day.

    Return the next day, remove the outputs and discard them, and pulled the driver board. I found a resistor that went open at R42, 150ohm. Replaced it. Found the right side drivers to be open as well, replace them with MJE15032 & 33. Went over ALL the other resistors, replaced out the 180Ohm resistors at R33 and R34 as they were out of spec. Everything else seems to check out fine.

    None of the small bean transistors test shorted or open. A few appear replaced, so I left them alone. Checked the bias controls, still working and still good. I checked all the emitter resistors, all check correctly.

    I replace the outputs in the CORRECT compliment, go over everything else, power it on, I hear the relay click on after a few seconds, all is well for about 20 minutes, then both meters spiked halfway up, a hum, then BAM, smacked a 10 amp fuse, and smoked the right side outputs AGAIN. Various obscene words were said, and the feeling of dumping gasoline all over it, and setting it on fire sounded good.

    And that's where we sit today. I have not touched it again. I just went over the driver board again today, and everything appears to be in the same state as when I repaired it. I did not find anything blown, burned, out of spec or shorted.

    I know this is my fault for not paying attention and I accept that fact, now I have to deal with fixing this issue.

    What should I start with?
     
  2. RuairiMutt

    RuairiMutt Member

    Messages:
    54
    Location:
    Lake Geneva, Wisconsin
     
  3. DougBrewster

    DougBrewster AK Subscriber Subscriber

    Messages:
    411
    A good start would be a DBT if you don't already have one...
     
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  4. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,883
    Location:
    uk.. the middle bit
    may have it running too hot ..bias too high
     
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  5. RuairiMutt

    RuairiMutt Member

    Messages:
    54
    Location:
    Lake Geneva, Wisconsin
    Yes I believe this was the issue. I went over and found a blown 2SA1209 transistor, which I do not have a sub for, so I ordered out the correct parts, and will be replacing these. I'm going to go over everything again, this time I'll be using MJ21193 and 94 complimentary pairs. The transistors that went up in smoke when I redid it, were old Toshibas I had that tested good. The OnSemi ones are every bit as good so I am not going to cry over the Toshibas.

    The driver is fully recapped now, and I also went over another techs bad handy work before mine.

    Before I try it again, I have to go in and repair the protection board. Someone deleted the relay, and installed a different one connected by wires off to the side. I have the correct relay. I have no idea why this 9090DB was so brutally hacked on.

    And my dumb self made it 10X worse. As a tech with common sense, I'm *greatly* reducing repair costs on this to that of a simple repair.
     
  6. slimecity

    slimecity Super Member

    Messages:
    1,961
    Location:
    New Zealand
    Just what I was going to say....could've saved this whole situation.

    Hey, we've all been there.
     
  7. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,150
    Location:
    Glen Burnie Md.
    +3 for a DBT. Get it running on the DBT and MAKE the BIAS AND OFFSET ADJUSTMENTS. LET IT RUN LIKE THIS FOR A WHILE. If everything ok, then BACK OFF ON THE BIAS to MINIMUM SETTINGS, then turn off and remove the DBT. (This is called ticking the Dragon). Plug it in to the wall and turn it on. While checking voltages check that operation is acceptable. If so reset the offset to spec, then raise the bias in increments and let it cook a little while you keep an eye on it. Once you get the bias up to spec, run thru the voltages again to make sure nothing is out of ordinary, and the bias is holding steady. If it's jumping all over the adjustment pots could need to be replaced. It's happened before and I won't say it won't happen again but the adjustment pots don't age well in Sansui's and or Pioneer's. 3386 series Bournes trimmers usually perform quite well for this.
     

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