SX1980 Power supply board ...... OH NOOOOOOOO!!!!

Discussion in 'Pioneer Audio' started by kevzep, May 14, 2017.

  1. kevzep

    kevzep Its all about the Music Subscriber

    First job today, mount that 13V pass transistor on the main heatsink.....there is a 220mV current draw on this supply so no issue, it just runs hot!! Needs a lot of heat dissipation that sucker.....
    I would recommend mounting the +/-80V and the 13V pass transistors on the main Heatsink, wouldn't worry about the 8V, doesn't run hot enough to justify moving it in my opinion....

    Going to have a look at this tuner issue and re-cap the rest of this beast now...

    Everything is nice and cool in regulated supply world, very happy with that!!
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  2. kevzep

    kevzep Its all about the Music Subscriber

    So, I'm at this stage of the game now, working my way through these boards, the AWF-030 was a bit of a horror show, not exactly how it was functioning....one of the regulators actually just fell out of it when I removed it from the case....
    So I did some serious work to that board.....
    I'll probably get to the tuner tomorrow, kind of ran out of time today....
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  3. kevzep

    kevzep Its all about the Music Subscriber

    Okay, so everything is coming along nicely, caps and most transistors are done.
    I've checked all functions, its all working nicely except for this tuner.

    As per MTF's instructions, I have performed the checks for the relay in the APC , and the relay is functioning correctly.

    However there is a new symptom.
    Hand on the tuner control, it goes into fine tune mode as it should, Fine tune LED is lit, and when you get onto a station, the Stereo LED is also lit.
    When you take your hand off the tuner control knob, the tuning meter shoots off to the right hand side and the audio starts pulsating, this pulsating also has the Quartz Lock LED flashing on and off in time with the meter going back and forth.
    Also, you can hear that relay clicking in and out, and of course the audio is pulsating and there's a lot of static along with the next radio station along the dial bleeding though....

    So hopefully this is something I can look at and its not an alignment issue. It does reek of component failure....
    I'll get in the manual and see if I can figure out how this part of the tuner circuit works....

    So the first pic shows it when your tuning in touching the tuning control knob.
    The second pic shows what happens when you let go of the knob.
    You can't really see, but that Quartz LED is flashing very very fast......Sometimes the pulsing will change from rapid pulsing to slow pulsing....its kind of random as to whether it will go fast or slow...
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  4. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

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    Have you set the APC reference frequency as described in the manual ?

    Or better yet, with a decent frequency counter? I believe it is 6.4 MHZ, and it needs to be 6,400,000

    The procedure was set up for shops that had yet not gotten decent frequency counters.

    Just like the Lissajous method for setting the PLL's VCO to 4x the 19,000 hz stereo mpx pilot frequency
     
  5. kevzep

    kevzep Its all about the Music Subscriber

    Ah yes, good, I will do that, I didn't want to forge head with something that could get me into trouble.
    It is 6.4Mhz, I have been studying up on it, and the APC in general, I believe this is where the problem is.....

    I'll report back after I have set this, hopefully we'll be closer to the problem or may even solve it.
     
  6. kevzep

    kevzep Its all about the Music Subscriber

    Well, that was easy. More hidden shenanigans from the Muppets!!

    I went to set the APC up, and I was wondering why the oscillator wasn't working....That totally explains the tuner behavior. I did stand there staring at the scope for a while, tried another probe and then used my intelligence to determine that there was no output from the oscillator.
    So measuring around in there I could see instead of 5VDC on Pin 2 of the AWX-124 board, I had 0.6V DC.
    This took me for a tour around the AWX-124 board for a while until eventually it took me back to that damn AWR-154 board.
    It seemed the Muppets had been in there modifying things and putting things on the 5V supply that had failed and shorted the 5V supply out, so of course the voltage drop resistor was thermonuclear.
    After I removed this offending article, we were in business. I must have missed this when I did the rebuild on the 154 board, stupid me, I saw the 8V working so assumed the 5V was all good, NEVER ASSUME!!!

    So the APC adjustments were quite straight forward, dialed it in, and it was all there working as it should...

    Now to do the function lamps....
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  7. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    Well done.
     
  8. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    tenor.gif
     
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  9. kevzep

    kevzep Its all about the Music Subscriber

    Thought I'd fit the front back on now that those Muppet shenanigans have been sorted....
    Just waiting on Dave's awesome Bulbs to arrive then I can fire those in and give this puppy back to the client...
    Although frankly, its going to be a welcome addition to my tech room for some high quality listening while I get onto the next thing which is a Sansui QRX8001........BOOOOOOOOO!!!!

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  10. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    Damn that a good looking unit!
     
  11. kevzep

    kevzep Its all about the Music Subscriber

    Oh yes indeed it is!! Now I want one!! The tuner is insane!! Gotta say it does rival my McIntosh MR78 and that is no lie!!

    Right, I am going to hunt one of these down!! Look out!!
     
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  12. Overundr1

    Overundr1 AK Subscriber Subscriber

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    The SX-1980 when tuned up certainly is a gem although my G9000 sitting above it in the rack never backs down from a head to head challenge :)
    Nice work on the tuner, one of these days I need to get mine back on the bench and fine tune that quartz lock circuit as mine is somewhat fussy still.
     
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  13. kevzep

    kevzep Its all about the Music Subscriber

    Doesn't take too long to dial in the APC, I remember my G9000 was pretty good, not as good as I was expecting mind you as they are rated very highly. I was however very impressed with the G22000, I'd like to have a shootout with the 1980 and G22K tuners.....I think the Pioneer might have the edge.....

    It was very satisfying to be able to sort the tuner out, its easy to immediately think you're into "tuner Voodoo world" and it lies beyond what we can do with basic test gear....The owner is absolutely ecstatic about it, I told him I couldn't promise anything. He said he would use the tuner if it was working, he told me it never worked at all before I got to it....

    Gotta test out he phono pre today, I didn't have any vinyl with me at the shop yesterday, so that will be its last test...

    Then I'll use it every day until the bulbs turn up to make sure its all good, and for my basic personal enjoyment!!
     
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  14. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Did you also notice how much cooler things are underneath with the transistor relocation?
    Volume control at 10 o'clock tsk tsk try it at 1 o'clock (grin)
    And I really hope those are not monstrous main caps under the scope rack awaiting a mad scientist over the top amp project :)
     
    Last edited: Jun 8, 2017
  15. kevzep

    kevzep Its all about the Music Subscriber

    Yes things are a lot cooler under there, the 8V regulator runs at 50˚C which is warm, but not hideous, so I think that will be fine.

    Those are electric Jug's full of water, 4 of them in parallel to make 7.9Ω, 2200watts each, so nearly 9,000 watt load right there, I run the Crown Macro-techs up on that load.

    Oh, believe me, this afternoon, there was plenty of 1 o'clock action!!
    I'm growing quite attached to it, I told the owner if he ever wants to sell it, I'd like 1st option. He said he was considering it, but not sure at this stage......Maybe I can tempt him with a McIntosh amp hahahaha....
     
  16. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    :rflmao::rflmao:... I knew it! Something tells me that the owner is going back with something but the mighty 1980!
    :beerchug:
     
  17. quaddriver

    quaddriver 120 What's per channel Subscriber

    I thought the same thing...
     
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  18. Glenz75

    Glenz75 Sansui and Pioneer Freak

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    What a great thread and completely fantastic rebuild on that one Kevin. Makes the SX1280 seem like a walk in the park really! I know of a working SX1980 down here in Wellington and its only going to be a matter of time before it too will need this type of rebuild when the power supply finally gives up!
     
  19. kevzep

    kevzep Its all about the Music Subscriber

    Thanks Glen, it was a bit of a journey alright, the owner got a bargain on the rebuild for sure. I never posted it in this thread, but I was about to put the front back on it and decided to go ahead and de-solder all the switches, dismantle and clean them, even though everything worked, I suspect it would only be a few weeks before things started to go intermittent..
    I'm glad I pulled them and cleaned them, they were pretty gummed up and oxidized with that black tarnish....

    So I wait for the panel lamps to turn up and in the meantime whilst I am working on this Sansui QRX8001, I am enjoying listening to the SX1980!!
     
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  20. Glenz75

    Glenz75 Sansui and Pioneer Freak

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    There's always something 'extra' that crops up after a big job and just when you're think you're done..hehe. Good to hear that its running like a Swiss clock now and so it should! Those push button switches on the Pioneers are a pain to get to on some models as well. A QRX8001? I worked on one of those a few years ago :)
     

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