Restoring uncle's Sansui 9090DB

Discussion in 'Exclusively Sansui' started by Juan9568, May 5, 2018.

  1. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
    Hi guys. I'm about to begin with the restoration of my uncle's old Sansui 9090DB. The receiver is in a pretty bad condition, it has been serviced by bad technicians and they replaced parts with cheaper or wrong ones.

    Issues:

    . Burnt resistors
    . Blown fuses
    . Blown outputs
    . Scratchy pots

    A few months ago I decided to start with the restoration myself as there are no good technicians where I live and trying to get quality parts it's almost impossible.

    I decided to do the following:

    . Rebuild from scratch F2624 Driver board
    . Replace capacitors and resistors from F2656 Power supply
    . New fuses
    . New outputs
    . Clean all pots

    Because I'm not an expert in electronics I thought it would be easier for me to start with a new F2624 instead of troubleshooting the whole board. So I got the new F2624 PCB and most of the other parts from mouser and digikey.

    Also built myself a DBT cause I don't wanna blow everything up on the first run but I don't know yet what type of bulb I need to use for the thing to protect the amp, I got a 70W but don't know if it is the right wattage. I'm on a 220v area. Any suggestions??

    What most scares me is when time comes to adjust the DC and Bias current, I know it is a very fragile thing and needs to be done correctly.

    I would really appreciate it if someone can give me any tips, tricks, suggestions so I can make this restoration right.

    THanks!!!


    Here are some pics of the amp before I begin. I will be posting updates on my progress.

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
    bolero and HarmanKardon like this.

     

    Please register to disable this ad.

  2. HarmanKardon

    HarmanKardon Tubes still smell funny Subscriber

    Messages:
    52,491
    Location:
    Schwarzwald, Deutschland
    You know that this receiver is a vintage Hifi legend?

    Good Luck! :thumbsup:
     
  3. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
    Yeees! I had the opportunity to use it when it worked and it sounded amazing. That's why I want to keep it alive. Hope I can!

    Thanks man!
     
    HarmanKardon likes this.
  4. dpcornell

    dpcornell Member

    Messages:
    60
    Location:
    B'More
    I'm about to work on a 990DB so I will be watching. I found this thread: http://audiokarma.org/forums/index....ted-here-is-a-recent-replacement-list.426901/
    Here is some advice from that thread:
     
  5. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,326
    Location:
    Boston
    You got the DC/Bias directional label correct as per the new PCB. That's good. You won't get confused.
    • I start the bias/DC offset procedures with a DBT.
    • Bias trimmers all the way down on both channels and DC offset trimmers at 2.6KΩ.
    • I turn the unit on and as soon as the relay clicks, I start a timer and monitor my DC miliamp meter for 4 minutes.
    • It's important to notice the meter right away and make sure it reads low (about 3 or 4 mA) so we know we turned the trimmers the right way. The DBT lamp won't like it if we mess this up!
    • I gradually increase the bias current with the trimmer until I get 28mA at the end of the 4 minutes run. I do this for both channels.
    • Two meters are nice to have, but when only one is available, I give the unit 20 minutes to cool down between biasing each channel.
    • Then I adjust the DC offset as close as possible to 0 mV. It's typically fluctuating +/- one or two mV and that's normal.
    • Then I bias again and after that it's time to move to mains voltage.
    So why 28mA? Because when going to mains from DBT there's always an increase of about 2mA in bias current.
    I set the final 30mA on mains.

    Do not stick the probes down there at the fuse and hold them for 4 minutes. You can clip them, but better use a spent fuse tool.
     
    Last edited: May 6, 2018
  6. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina

     

    Please register to disable this ad.

  7. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
    Thanks Tom. What wattage would be the right one to use for my DBT bulb? I'm on 220V
     
  8. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,326
    Location:
    Boston
    70 - 100 Watts. You're safer with 70 but it could too easily give you a nice scare when the bulb goes bright. 100 watts if you know what you're doing.
    Whatever you choose, stick with it for a while as there's a learning curve in interpreting what the bulb is trying to tell you.
     
  9. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
  10. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
  11. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,326
    Location:
    Boston
    Looks nice! I'd wrap some shrink around the STV-3HY leads or make sure the systoflex goes all the way up, so it doesn't short with the heat sinks by accident.
     

     

    Please register to disable this ad.

  12. DougBrewster

    DougBrewster AK Subscriber Subscriber

    Messages:
    474
    +1
     
  13. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
    True, I'll check that
     
  14. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
    Hipocrates likes this.
  15. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
    I'm trying to bias the amp but the green light doesn't come up...It stays on blinking red. The DBT bulb turns on but immediately starts dimming...Could it be that the 70w bulb DBT doesn't let the amp power up correctly??? without the green light I still can read 2mA on the bias


    Unit has been off for years...Maybe old capacitors need time to charge on DBT??


    Here a video:

     
    Last edited: Jun 7, 2018
  16. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,326
    Location:
    Boston
    That's expected while the main filter caps are charging. If the protector circuit "protects", it prevents DC from getting to the speakers. Most likely you got too much DC. While the red led is flashing, you can measure it for each channel on the gray and blue wires (each against chassis) coming out the bottom of the PS board. This will indicate if you got a DC issue.
     

     

    Please register to disable this ad.

  17. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
    Should I measure these blue and gray wires with F04 and F05 fuses in the circuit?
     
  18. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,326
    Location:
    Boston
  19. Juan9568

    Juan9568 Member

    Messages:
    53
    Location:
    Buenos Aires, Argentina
    Thanks!...

    Sorry again...I'm reading negative voltage

    Is this ok?

    Red probe--->gray wire (left channel)
    Black probe--->chasis

    Red probe--->blue wire (right channel)
    Black probe --->chasis
     
  20. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,326
    Location:
    Boston
    yes, good, keep the black probe on the chassis. you can get negative reading. How much?
     

Share This Page