AU 20,000 No Power

Discussion in 'Exclusively Sansui' started by sansuilove, Aug 1, 2017.

  1. sansuilove

    sansuilove Active Member

    Messages:
    243
    Hello
    Few weeks ago, noises started coming from the left channel of the amplifier .
    Took it to a local tech and few days after he contacted me claiming he 'found' a small spring at the power amp boards that made a big mess and unit does not power on any more.
    After arguments with him that I took him a working unit I decided to take the amplifier back to me.
    The fuse on the back (6A -220/240 voltage)
    Was blown.
    Replaced with a new one and fuse blew again.
    Took his advice and removed ALL 12 output transistors .
    Tried to turn it on again and nothing - no power
    Checked all fuses on the protection board and all are OK.
    What should I be looking for?
    Would appreciate your help.
     
  2. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,199
    Location:
    Costa Rica
    What outputs did you use?
    Is the power switch working?
    I'll test the transformer and the rectifiers first, and test voltages from there with the schematics on hand.
    Hang on, someone with more experience will chime in.
     
    Overundr1 likes this.
  3. sansuilove

    sansuilove Active Member

    Messages:
    243
    Didn't use any new transistors - just pulled the originals out.
    as far as I know it works but worth checking
    Your answer is pretty contributing And gives me a way of working
    Thanks
     
  4. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,199
    Location:
    Costa Rica
    Way more than that, it deserves a nice restoration :thumbsup:.
    Sadly I've never have the opportunity to get one, so I don't have experience with that unit.
    How are your skills regarding electronics? Can you read schematics?
    Do you have the service manual?
    Check f-2511 and lets wait for more help.
     
  5. slimecity

    slimecity Super Member

    Messages:
    1,954
    Location:
    New Zealand
    What does this mean?

    As you have pulled all the output transistors - have you tested them with a meter? Testing instructions are at various places on this site.

    Your immediate problem appears to be a loss of power however. No click? No indicator light?

    I agree that you need to start by finding the service manual and testing that you are getting firstly, primary power to the transformer and then secondary power from the transformer. Are you confident doing this, as you will be dealing with high voltages. Plus this amp is not the most straightforward to work on.
     
  6. sansuilove

    sansuilove Active Member

    Messages:
    243
    I have good electronic skills and ability to read manuals and schematics .
    I recapped the amp 3 years ago but power switch didn't get any treatment.
     
  7. sansuilove

    sansuilove Active Member

    Messages:
    243

    He contacted me saying that he found a spring came from somewhere and touched the power amp boards or driver boards and made this mess. What I think is he just made a mistake and fried something and now trying to wash his hands off - credibility issue.

    No click - no protection light
    Will check the power at transformer and let you know guys
    Thanks
     
    Hipocrates and slimecity like this.
  8. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,199
    Location:
    Costa Rica
    You know more than me then!:p
     
  9. wlhd1610

    wlhd1610 Penny and her new friend Subscriber

    Messages:
    2,023
    Location:
    upstate new york
    There are several good threads here in the Sansui forum on the AU-20000.
    An absolutely excellent one by akr kale.
    Check it out!
    I also had the honor of restoring one of these fine amps last fall.

    Bob
     
  10. w1jim

    w1jim I can fix it but good... Subscriber

    Messages:
    7,165
    Location:
    Boston western 'burbs
    Download the service manual from HiFiengine.com.
    First thing - with the power tranisistors removed or the power removed from them check the power regulator board for correct voltages.
    In my experience the power regulator board gets very hot which seriously degrades the solder joints.
     
    sansuilove likes this.
  11. sansuilove

    sansuilove Active Member

    Messages:
    243
    Output transistors are all out of amp.
    Pulled all connectors out of F-2511 protection amp and tried to get some readings out of the transformer - couldn't find my way very well .. I get only 60VAC out of the yellow wires (9+11)
    How do I identify the primaries from the secondary?
    I'm starting to suspect the transformer is bad..which is the worst scenario I can think of :(
     
  12. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    40,560
    Location:
    Hertfordshire, UK
    Do you understand 'soft start' circuits? - check the soft start resistor(s).
    I would also worry about this, there has been some chat here on AK about the absence of main rail fuses in this model, and if there is a serious short circuit on the main rails, (as appears to be the case here), what this could mean for the safety of the transformer - made vulnerable by this omission.

    Read Troubleshooting section 3.1, subsection 1, in the service manual.
     
    Last edited: Aug 7, 2017
    richardpp likes this.
  13. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
    2,282
    Location:
    Mississippi
    Disconnect the transformer leads from the circuit board.
    With dmm set to measure ac volts---
    Measure each wire to ground, not to each other btw.
    Blue wires 46vac
    goes to pins 5 and 6
    Yellow wires 60vac
    goes to pins 9 and 11
    White wire 5.7vac
    goes to pin 14 and 15
    Red wire 22vac
    goes to pin 12 and 13
    This will indicate transformer condition.
    If you are using a dim bulb tester (recommended) there will be about a 10% voltage drop from these readings.
     
    Last edited: Aug 6, 2017
    richardpp, Hipocrates and Hyperion like this.
  14. sansuilove

    sansuilove Active Member

    Messages:
    243
    Ok I located Black probe at speaker ground terminal
    Readings :

    Yellow #1 - 27Vac
    Yellow #2 - 27Vac
    Brown #3 - 20Vac
    Blue #5/6 - 0
    Green #10 - 2Vac
    Red #12/13 - 5Vac
    White #14/15 - 9Vac
    Yellow #9 - 1.9Vac
    Yellow #11 - 1.9Vac

    Measured R01+R02 on f-2511 :
    R01 - 0.9M !!!
    R02 - 3.9 ohm
    It made me a bit confused because on the resistor it says 3.9K but service manual says 3.9 ohm
    Ordered a new pair already
     
  15. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    40,560
    Location:
    Hertfordshire, UK
    That isn't a confidence inspiring list of voltages.
     
  16. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,199
    Location:
    Costa Rica
    Can be possible that the transformer is shot?
     
  17. sansuilove

    sansuilove Active Member

    Messages:
    243
    :(I can't express how angry and upset I am if it's true
    Could be that the power switch isn't making a full contact or has some kind of malfunction?
    Any thermal inner fuse?
     
    Last edited: Aug 7, 2017
  18. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
    2,282
    Location:
    Mississippi
    Possibly, be very carefull here working with mains voltage. If you have a switched outlet in the rear of the unit measure ac across the two slots when power is applied.
     
  19. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,199
    Location:
    Costa Rica
    Let's wait what the others say, but if we compare what Overundr1 voltages say... Did you did the trobleshooting chart on page 4 of the service manual? Maybe something else is faulty in addition to resistors.

    Capture.PNG
     
  20. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
    2,282
    Location:
    Mississippi
    Even if readings are 1/2 wave they look suspicious.
     

Share This Page