Pioneer QX-949A Power Switch Needed

Discussion in 'Pioneer Audio' started by Davron94, Feb 11, 2016.

  1. QSilver

    QSilver Super Member

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    You need a paticular Triac listed in the thread - it's called an Alternistor and doesn't need snubbing - so you can remove the ceramic caps on your power switch. The power switch then acts like a gate trigger and you wire the Live in to the power switch. Then, from the power switch you connect a 100 Ohm resistor and then connect that to the Gate leg of the Alternistor.

    You connect the main live coming into the unit to the Alternistor's MT2 leg.

    Then you connect the transformer primary that would have come from the switch, into the MT1 leg of the Alternistor.

    Hope that makes sense - don't try it unless your absolutely sure - also, be sure to get the insulated tab type Alternistor - means you dont have to isolate the metal tab from the chassis.
     
  2. Davron94

    Davron94 Active Member

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    Thanks, this gives me a better understanding of what to do.

    Would this be the type of alternistor? :

    http://www.mouser.com/_/?Keyword=alternistor&FS=True

    I don't see any description of insulated tab on any of these though.
     
  3. audiojones

    audiojones Jonesin' for audio Subscriber

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    Right, what QSilver said :thumbsup:. Also if you google the Littlefuse Q4025L6 you will find the spec sheet with the pin layout diagrams so you'll know which pin is which. If you are looking at the device from the front the pin layout is: Left pin=MT1 middle pin=MT2 right pin=Gate so from there you simply follow the wiring diagram. Remove the snubber capacitor on your existing switch and redirect the main power from the cord to the MT1 terminal on the triac. From the MT2 terminal you send a wire to one side of the power switch and to the transformer supply lead. The Gate terminal goes through a 100 ohm 1 watt resistor to the other end of the power switch. Mount the triac to a flat sheetmetal panel somewhere inside the receiver and use a dab of thermal compound on the tab for better heat transfer and you're done. Make sure to use heat shrink tubing on all of the connections, it's all line voltage and has to be safely insulated.

    Hope this helps!
     
  4. QSilver

    QSilver Super Member

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    Q8025L6 - Yes that's the one I used. it has a very high rating so it can take the punishment a reciever or amp will give it at switch on AND it's actually a bit kinder to the electronics as a Triac will only start to conduct at the 0V crossing point of AC so when you press the power button, the triac effectively waits for the AC to cross 0V and begin to rise before letting it through to the unit meaning that your electronics and transformers rise from 0V to working voltage rather than snapping on at whatever is there when you press the power button.... if that makes sense?

    Am I missing something? That doesn't seem right to me...

    When I did this on my QX-8000, my power switch was switching both live and neutral on and off. Seen as this isn't strictly nessacary and wouldn't suppiort the triac mod, I rewired the input and connected the neutral directly to the neutral of the switched socket on the back and one of the primary wires in the transformer.

    Then I sent the Live to the power switch AND to MT2.

    Then I connected MT1 to the other primary winding wire of the transformer - completing the circuit for the transformer.

    Finally I connected the switch to the Gate leg via a 100 Ohm resistor - though IIRC mine was a 0.5W resistor but I might be wrong there...

    Just wanted to make sure we're understanding each other correctly as its all line voltage which is potentially deadly.

    If you are unsure when you come to power it up for the furst time, build a Dim Bulb Tester and power it up on that to make sure its all safe.
     
  5. audiojones

    audiojones Jonesin' for audio Subscriber

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    Take anoher look at the wiring diagram and the description in post #1 by k7sparky, he spells it out pretty clearly. The gate gets switched through a 100 ohm resistor from MT2 which is also the line that splits off and goes to the transformer supply, MT1 gets the power from the cord. I've done this on a bunch of receivers and it works beautifully, hopefully it's not a typo (which I doubt as it would have been caught long ago). Hope he doesn't mind me putting the image of his schematic in here:
    [​IMG]
     
  6. QSilver

    QSilver Super Member

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    1,093
    I think I see what your saying... But the power switch gets fed from the power cord too? and then goes from the switch, through the 100 ohm resistor...? Think I'm getting confused... :confused: I'll go re-read... maybe a diagram would be best...

    Attached is how I did it. It seems to work just fine...

    Ah I see the difference - I put the Triac on the Live side, and the original design was put on the Neutral side. Either works I guess. I get it now. :thumbsup:
     

    Attached Files:

    Last edited: Feb 17, 2016
  7. Watthour

    Watthour Electron Rancher - JS3600

    The output of the power switch will get connected to the gate lead of the triac, probably through some fixed resistor. The M or MT leads will connect to the AC supply and load (where the switch leads previously were connected). In essence, the triac becomes the switch, and the old power switch merely gates up (turns on) the triac.
     
  8. audiojones

    audiojones Jonesin' for audio Subscriber

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    Nope QSilver, the power switch doesn't get tied to the live line from the cord - only terminal MT1 (M1 in the diagram) gets tied directly to the line. There is no neutral side because the plug is non-polarized. The other side (coming off of MT2) is the load side that supplies the transformer. This is the line that is supposed to feed the power switch, then the other side of the power switch goes through a 100 ohm 1 watt resistor and gets tied to the Gate terminal. Not sure if it's actually taking the load off of the switch the way you have it hooked up but you're supposed to switch the gate with MT2.
     
  9. Davron94

    Davron94 Active Member

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    Ok, This is all great information, so thanks to everyone for helping me out.

    Let me see if I got this straight now.

    A/C line in >>> M1
    Transformer Line (Line removed from Power Switch)>>>M2
    Gate with resistor >>>Power Switch connection formerly going to Transformer
     
  10. audiojones

    audiojones Jonesin' for audio Subscriber

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    Yep, you got it but remember that the line going from M2 leading to the transformer splits off and feeds the other end of the power switch. That's the leg that gets switched to operate the Triac. Also don't forget to remove the arc suppressor or "snubber" capacitor from your existing switch, it may cause false triggering of the Triac and it's not needed anymore.
     
  11. Davron94

    Davron94 Active Member

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    Is the transformer line already split, or do I need to create another conductor line? And, at the other end of the power switch, the leg that gets switched to operate the Triac, is that connection on the switch already free or does a line need to be removed from it?
     
  12. audiojones

    audiojones Jonesin' for audio Subscriber

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    Dunno, you're going to have to follow out the wiring in your particular unit. In mine the wires were all cut and the switch was missing, but it was all pretty straightforward like any other receiver. Just follow the wiring from the power cord to the existing switch, then from the switch to the transformer. You'll have to re-route some wiring and probably add a splice to split the transformer lead over to the switch. In my case I soldered wires and the 100 ohm resistor leading to the Triac directly to the switch but I desoldered and removed all of the old wiring and the snubber beforehand so I had room to do that. Please do any wiring carefully and safely, and make sure to insulate all connections very well. I like using heat shrink tubing for this, makes for a nice neat and professional looking job.
     
  13. jblmar

    jblmar JBL & marantz

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    Some switches are the '227' type sold at Digikey or Mouser for a few bucks.
     
  14. Watthour

    Watthour Electron Rancher - JS3600

  15. Davron94

    Davron94 Active Member

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    That is correct, however, on international models the switch is different due to the A/C input being adjustable. In this case the ASG-070 is the power switch that is used according to the service manual.
     
  16. Watthour

    Watthour Electron Rancher - JS3600

    In the case of installing a relay in lieu of the triac, the single pole switch would work.
     
  17. Davron94

    Davron94 Active Member

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    Thanks but that might be a little bit advanced or entailed for for me
     
  18. Watthour

    Watthour Electron Rancher - JS3600

    It's really no more difficult than installing a triac. Consider that the relay IS the triac and all the same wires go to essentially the same places, with the addition of one wire for the opposite side of the relay coil.
     
  19. Goldfingers

    Goldfingers New Member

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    Well, to bring some new life to this informative thread; I have a 949A, needing a ASG-070 or replacement/equivalent switch. My switch wont hold its position when pushed, so either it needs a lot of TLC or I can try to find a fitting, non original switch. The digikey I read about here is only for 125 and I need a 240 version. Does anyone of you gurus here know of any such switch??? Any help would be appreciated. I read that triac approach but that is way to complex and over my head for me. So ...anyone?? Thanks !
     
  20. White_wolf

    White_wolf Active Member

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    I found a QX- 949A, not sure if I still have it or not. The power switch was missing the previous owner had hot wired the power so any time the unit was plugged in it was on.
     

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