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SX-950 Looking for help bringing it on home!

Discussion in 'Pioneer Audio' started by EricFossen, Aug 2, 2018.

  1. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    I've have an sx-950 that was in need of a recap. I had borrowed it to my brother in law 8 months ago and he returned recently reporting it was "fuzzy". When I hooked it up it sounded good for about 4 LPs and then sure enough it was fuzzy. I did a full recap with the exception of tuner and main filters. I put it back into my system and listened to it for 4 days. It sounded much better, but by the 4th day it didn't seem as detailed as it should have been. Since I hadn't replaced any of the known problematic transistors I went back in and changed out the 726's and 1313's with 992's and 1485's in the phono stage. It passed the DBT, so onto the Power Amp assembly. I swapped out the 726's there and it failed the DBT! 4 transistors from the finish line and I'm stuck. I've looked for loose wires, bad solder joints, proper pin out, made sure the outputs were snug and tight. I went back in and re-soldered 922's, no change. Went back in again and replaced the 1uf and 2.2uf caps on right side. When I was de-soldering the 726's on that side I was wiggling one of those two caps thinking I was wiggling the 726 to loosen it up. Thought maybe I had a loose lead. No improvement. The leads on the small horseshoe shaped resistor that screws to the heat sink are intact. I thought now was as good a time as any for suggestions as how to proceed. I don't thing it's a good idea to continue to disassemble the outputs from the heat sink and manipulate the power amp board without a plan. It feels like I'm so close. I would really appreciate any assistance with where to go from here. Can I do pin voltages with the receiver on the DBT?
     

     

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  2. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,578
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    check pin-outs of 726's
     
  3. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    726's were replaced with 922's. 726's are BCE Pinout and 992's are ECB, so 992's face opposite direction as 726's. Correct? I'm guilty of settling for not taking a better picture of the board before I proceeded. Really thought I was home free. I've been over pinout a couple of times , but will do with a fresh eye tomorrow and take pictures of current situation. Could replacing suspect 726's cause a problem elsewhere on the board?
     
  4. petehall347

    petehall347 the brandy coffee man Subscriber

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    all i see is after changing them it went bad . did you test the old ones ?
     
  5. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    OK Pete, I checked the old 726's with the DVM and they all checked out alright. I'm going to reinstall them and see if it passes the DBT. Thanks for your help tonight!
     
  6. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    Here are pictures for where I'm starting from today. I re-checked pin out on 992's and checked against work I did on phono board. I'm going to pull the 992's and check that I didn't get a bum transistor. I'll also reflow solder joint on 330uf cap. I had to use a 63v instead of 10. It is taller and is taking some abuse when I move board to solder. If 992's check out, does it make sense to put 726's back in?
     

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  7. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
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    In removing 330uf cap at C12 I found a lifted trace on +. It is only slightly lifted. I'm hoping this is the problem. How can this be fixed? I thought I've seen past posts where guys use super glue and a toothpick. Either way I will order the right size cap as this was probably caused by cap rubbing on chassis during transistor replacement. I'm going to leave unit open and hopefully someone can chime in with an answer. Thanks.
     
  8. petehall347

    petehall347 the brandy coffee man Subscriber

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    27,578
    Location:
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    it may have been shorting if touching the chassis .
     
  9. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    It ran fine after initial recap before transistor replacement. I'll be ordering a new transistor, but in the meantime how do I address the lifted trace?
     
  10. petehall347

    petehall347 the brandy coffee man Subscriber

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    if trace is intact it can be glued down .. if not just bend the lead over and solder to where to trace is stuck down .
     
  11. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    Thanks! Hopefully this is the problem. I appreciate your assistance.
     

     

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  12. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
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    Got 330uf/10v caps today and installed. I glued down lifted trace on C12. Still doesn't pass DBT. I'm leary of making more than one change at a time for fear that I may solve the current problem and cause another without knowing it. I also don't want to disassemble the heat sink/power amp any more than I have to. Any direction on how to proceed is appreciated. Thanks.
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

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    27,578
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    try turning the bias pots down to min bias .. and also check dc offsets
     
  14. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    Can I keep Jumpers in if I don't have a 5.1 ohm resister per the manual, or is there an alternative?
     
  15. petehall347

    petehall347 the brandy coffee man Subscriber

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    remove jumpers and turn vol to min select aux ..
     
  16. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
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    measured 1.92V between pin 9 & 10, pot adjusting pot didn't affect voltage at all. measured -1.689 between pins 24 &25, again adjusting pot did nothing. Was done hooked through DBT.
     

     

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  17. petehall347

    petehall347 the brandy coffee man Subscriber

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    and you turned vr1 vr201 ? if so we need to be looking at those replacement diff pairs more closely .
     
  18. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    yes, vr1 and vr2. You're talking about changing out pots right? I do have a set of pots that were supposed to go in a 980. Same pots?
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,578
    Location:
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    i suspect the new transistors at fault .. does your meter have transistor test function ? if so you can verify pin outs .
     
  20. EricFossen

    EricFossen AK Subscriber Subscriber

    Messages:
    36
    I did check the new transistors with the diode mode on my DVM and they checked out. Not sure what you mean by verifying pin outs. I have a DCA that I can ID leads.
     

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