SX-780 - Counterfeit Darlingtons?

Discussion in 'Pioneer Audio' started by clk1981, Jul 18, 2017.

  1. petehall347

    petehall347 the brandy coffee man

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    trying to get to bottom of this as i understand it you tried removing power from each module but only by disconnecting both allows the relay to click ?
     
  2. clk1981

    clk1981 Member

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    56
    yes, when power is disconnected from BOTH new modules (orange and red wires), speaker relay clicks, and I have sound via headphones, although distorted.
     
  3. petehall347

    petehall347 the brandy coffee man

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    i take it you removed both then added one at a time ? or a variation that is same thing .
     
  4. sregor

    sregor AK Subscriber Subscriber

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    When you remove the outputs, the circuit "floats' and you cant troubleshoot it correctly. If you add a 1k from the input of the stk to the output, then you can trouble shoot the rest of the circuit.
    Relay works with no STK because there is no signal into the protection circuit, so no problems seen.
    pins 0 and 1 are inputs 8 and 3 are corresponding outputs - so to test rest of circuit, add 1K resistor between 0and 8, and between 1 and 3.
     
  5. mxthunder

    mxthunder New Member

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    21
    i would suspect both are bad. even with my known bad resistors and stuff, with the one bad darlington removed, the relay clicked.i thought i was home free. my relay still clicked with new darlington in place, but no sound out of left channel and skewed voltages still.
     
  6. rcs16

    rcs16 Super Member

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    2,897
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    I am not 100% sure it is the STK darlingtons, but chances are, they are the problem. This is exactly why I designed the replacement module so that you know with a high degree of confidence that you should be able to fix the power amps in a sx-780 for the life of the unit.
    So I suggest that you make some up and take the guess work and frustration out of the repair.
     
    redk9258 likes this.
  7. clk1981

    clk1981 Member

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    56
    You make replacement modules? Do you have any for sale?
     
  8. tsd71

    tsd71 RIP Tom Petty Subscriber

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  9. mxthunder

    mxthunder New Member

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    turns out my ebay module was either doa or got killed because of faulty emitter resistors. swapped out a few resistors in the bad channel along with the .22ohm resistors and still no click when new darlington is installed. swapped the good channel darlington into the bad channel and it works fine now. i need to find a source for some good darlingtons
     
  10. rcs16

    rcs16 Super Member

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    2,897
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    To be honest, you are wasting your money and time in this quest, that is why I design a replacement to put an end to these rip offs.
     
    redk9258 likes this.
  11. mxthunder

    mxthunder New Member

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    21
    I saw that thread. are they available for sale?
     
  12. rcs16

    rcs16 Super Member

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    2,897
    Location:
    Baldwin, Ontario, Canada
    At this time, know one (me at least) is actually going to make them up and sell them since know one (people in need) seem to want to pay what it costs for someone to do it for them. So you have a few options.
    1) ask Zeb or someone else (tsd71?) to sell you pcbs, AL plates and you have to order the parts from Mouser/ or Digi-key etc and solder/assemble them yourself
    2) order your own pcb's,parts, make up Al plates, assemble them yourself.
    3) Some kind person takes it upon themselves to do it all for you
     
  13. mxthunder

    mxthunder New Member

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    Thanks for the info. I can probably handle the assembly and making some AL plates. I will do some more research and get a parts list together.
     
  14. tsd71

    tsd71 RIP Tom Petty Subscriber

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    There is no source for "good darlingtons" unless you find an audio shop that closed 15 years ago with a surplus of modules, I got lucky and bought all of them for $10 but they are all gone now so I'm building my own with the help of the rcs16 replacements. A little work goes a long long way.

    http://www.audiokarma.org/forums/in...050-replacement-for-sx-780-and-others.721181/

    Zeb has the direct contact with all the information on the boards to China, contact him, I'm gonna need some boards too soon so the more he orders the less the price should be.
    They are definitely high quality boards.
     
  15. rcs16

    rcs16 Super Member

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    2,897
    Location:
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    Hi tsd71,

    You can order your own pcb's from pcbway. If you know Zeb's order number then they can reference it so you do not need to send the data. Either that or simply just send them the zip file that includes the fab data. I gave instructions in an earlier post.
     
  16. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    3,996
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    I have an order for 50 PCB's on the way.
     
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  17. mxthunder

    mxthunder New Member

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    21
    Small update.... got a refund for the first darlington that was bad. took a chance on a set of 2 more off ebay. ohmed them out before installation, they checked out. threw em in, and whala. shes back in business. if they last 2 years, ill be happy. i cannot justify spending $300 to get it repaired right now. DC offset is in order and I think I am good to go knock on wood.

     
  18. Arthur Smith

    Arthur Smith Well-Known Member

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    692
    New original Darlingtons have not been available in quite some time, and will not be. You have to use what is available, and that is 3rd party knockoffs. The other alternative is to run a broken receiver as is. The knockoffs are not all junk, and there is one supposed reputable source in Georgia.
     
  19. MichaelFin

    MichaelFin New Member

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    21
    Any chance you have some left over? I'd be interested in buying one of those PCBs off of you.
     
  20. rcs16

    rcs16 Super Member

    Messages:
    2,897
    Location:
    Baldwin, Ontario, Canada
    PM him, I'd suggest that you buy 2 pcb's and the AL plates as well.
     

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