Sansui AU-X1, power supply problem.

Discussion in 'Exclusively Sansui' started by kryzpo, Sep 8, 2017.

  1. kryzpo

    kryzpo New Member

    Messages:
    23
    Location:
    Santiago, Chile
    Previously you helped me in these post:
    http://audiokarma.org/forums/index.php?threads/i-found-an-x1-but.776489/#post-10658635

    http://audiokarma.org/forums/index.php?threads/factory-or-tech-mod-au-x1.785688/

    Now, I recap the boards 2917-2918 (MC amp), 2770-2771 (MM amp), 2778 (reg power supply), 2774 (buffer amp). In the board 2778 I replaced a lot of resistors and transistors (a992 and c1845) that were affected by the corrosion of the glue. And obviously I've changed all the black flags.

    I connected the amplifier with a DBT without speakers connected. I am using a 75 watt bulb, in my country we have 220 volts.

    When I turn it on, without the boards 2917-2918 and 2770-2771, I get all the voltages perfectly (power source, power amp, bias, etc.) and the DBT turns on 1 (from 1 to 10). The power light is on and all the relays are activated. The only strange thing is that when I select the speakers in A + B, the power light blinks, but everything still works fine.

    When I turn it on, with the boards 2917-2918 and 2770-2771 in place, the voltages go down, getting 7.7v and 38v on the 2778 board. If I put the switch in MC, the amplifier goes to protection and the light flashes. If the switch placed it in MM, the amplier came out of protection, but the voltages still low.
    If the switch placed it in MM, the amplier came out of protection, but the voltages still low.

    I have not yet applied any mods to the phono boards. I only changed electrolytics and black flags on these boards.

    Harolda says that when connecting the amplifier without the DBT the voltages stabilize, could it be the same?
    http://audiokarma.org/forums/index....tor-replacements.684619/page-15#post-10810722

    Any suggestion is welcome :) Thanks!
     
  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    39,101
    Location:
    Hertfordshire, UK
    I think you have a fault on the MC amp board(s), causing the protection problem. And possibly wrongly installed capacitors? on the MC board(s), or the MM board(s), causing the low voltage problem.

    Treat this as two separate problems, you have the opportunity to remove either the MC board(s) or the MM board(s) which should help tremendously with fault finding - but double check your work on those boards for mistakes.

    See if you can find any combination of installed MC and MM boards that works correctly - i.e. not going into protection, and not pulling the voltage down. Don't forget to power down before each removal or insertion.

    And no powering up without DBT until those voltages look correct!
     
    Last edited: Sep 9, 2017
    slimecity likes this.
  3. kryzpo

    kryzpo New Member

    Messages:
    23
    Location:
    Santiago, Chile
    Hyperion, thank you very much for your help.

    I checked everything I changed, all the capacitors and transistors are in the right direction.

    I did the following tests and I think I have news.

    If I keep the 2719-2918 (MC) boards in place, without MM boards, the measurements are OK.

    But if I keep the 2770-2771 (MM) boards in place, without MC boards, the voltages (TP03-TP04) of the 2778 card (power source) drops to 38 volts. The TP01 and TP02 are in 10.3 volts.

    The same voltages feed the 2774 (buffer amp) board. So I also unplugged it and removed all the boards (MM and MC). Now all voltages are even better and the DBT virtually shut off. In addition, the light no longer blinks when I select the speakers in A + B.

    Hence, the more the load, the worse the problem.

    :(
     
    Last edited: Sep 10, 2017
  4. Bigdrive

    Bigdrive New Member

    Messages:
    38
    Location:
    Kelowna
    +1 what Hyperion says. I think it's two separate problems.

    The voltages should return to normal with the dbt removed. I would not do that until the protection fault is addressed.

    I guess that before you started you put the amp in MC and everything was OK, if that's the case, the problem has to be a fault/error on the 2778 board. Did you take the board completely out? If so maybe you refined wrong like I did. Anyway, that's what I think.
    I any case if you can wait til Wednesday I am more than willing to tell you what the voltages are on the cards with dbt installed. That's of coarse, if mine cooperates and fires up after my last a error. I am betting that Harolda is correct, and your voltage problem will fix itself but not until the protection problem gets solved. Good luck and let me know if I can help as my unit is at the same stage as yours.
    Cheers,
     
  5. Bigdrive

    Bigdrive New Member

    Messages:
    38
    Location:
    Kelowna
    It won't be as simple as the molex connector going to the wrong board?
     
  6. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    39,101
    Location:
    Hertfordshire, UK
    Agree the protection problem is the most worrying and critical problem, and also that the voltage problem might resolve itself when not on DBT - perhaps try a slightly higher wattage bulb? (100W?) - if the voltage readings go up with a higher wattage bulb the DBT may very likely be responsible for the low readings.

    And DO make sure you are installing the boards in the correct slots - each of the four boards have ONE correct slot according to the Service Manual - I don't know what would happen if installing them incorrectly, never tried it. :)
     
    Last edited: Sep 11, 2017
  7. kryzpo

    kryzpo New Member

    Messages:
    23
    Location:
    Santiago, Chile
    Thank you very much!

    I'll put a 100-watt bulb.

    I checked all the connectors 10 or more times. I took a lot of photos before unplugging the cables and boards.

    I hope to have news soon.

    Regards!
     
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  8. kryzpo

    kryzpo New Member

    Messages:
    23
    Location:
    Santiago, Chile
    News!

    I put a 100-watt bulb and the voltage now went up from 38 to 42 volts.

    Note that the amplifier is not in protection. The LED blinks when I place the MM cards, but the relays remain active.

    Is it time to try without the DBT? But first, tomorrow I will look for a light bulb 120 watts, still exist? :idea:
     
  9. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    39,101
    Location:
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    The above comment suggests you are plugging in boards with the power applied, if you are - please don't do this!

    Providing the protection light isn't blinking (=protection activated), and you get normal voltages (+/-11V & +/-47.5V with the Phono amp PCB's (x4) not installed, I think it will be OK to apply power without the DBT. I doubt you will find a 120W incandescent bulb, check and adjust the above voltages and the DC offset adjustments for the Phono PCB's as per the Service Manual.

    There have been at least three recent threads on AU-X1 reconditioning & rebuilding - If you haven't yet, I would strongly suggest you read them, bookmark them, and make notes. ;)
     
  10. kryzpo

    kryzpo New Member

    Messages:
    23
    Location:
    Santiago, Chile
    No, I explained myself wrong, my English is horrible haha. Each time I have placed or removed the boards I have done with the amplifier off.

    I forgot to mention that the MM and MC boards measure 0mv without problem.

    Believe me I have read all the posts :biggrin:.
     
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  11. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    39,101
    Location:
    Hertfordshire, UK
    OK - fair enough :thumbsup: - let us all know how you get on. ;)
     
  12. kryzpo

    kryzpo New Member

    Messages:
    23
    Location:
    Santiago, Chile
    :banana:

    Without the DBT the voltages read perfectly, and in fact, all voltages are perfect, and the amplifier works perfect.

    I thank you all very much. :banana:
     
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  13. ghamilton

    ghamilton Super Member

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    1,230
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    ASHEBORO NC
  14. kryzpo

    kryzpo New Member

    Messages:
    23
    Location:
    Santiago, Chile
    Haha, I knew it.

    When I finish with everything else I will upload photos.
     
  15. slimecity

    slimecity Super Member

    Messages:
    1,542
    Location:
    New Zealand
    Yea, show us your pics.

    My X1 is arriving in about a week or so.

    I will need all the guidance I can get......
     
  16. kryzpo

    kryzpo New Member

    Messages:
    23
    Location:
    Santiago, Chile
    I recommend you start with the regulated power suply. In my case, there was a lot of glue that corroded the legs of the capacitors. Two capacitors were out of order.

    And, of course, replace all the black flags.
     
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