SX-650 that took one on the chin . . .

Discussion in 'Pioneer Audio' started by watt, Jan 8, 2019.

  1. watt

    watt no on

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    or the tuning knob, or the source selector.

    IMG_1599.JPG

    Straight from the Goodwill Buy-the-Pound. So while I could complain about the damage, it's likely that that's why it was in one of the bins for me to find.

    The good news is that it powers up and seems to function well so far. The bad is that it needs new glass, a new source selector (there's no saving that shaft, I'm afraid), and I need to straighten the shaft for the tuning knob. Oh, and a knob for the source selector. And the vinyl wrap is peeling in some places. (This feels a little like the scene in Ghostbusters where Dan Aykroyd starts listing all of the mechanical problems with Ecto 1.)

    Do I need a project? Not really. But I'd like to shape it up a little in the name of preservation and "fun."
     
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  2. watt

    watt no on

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    I downloaded the service manual and started assessing things this morning. Removed the top and bottom covers and the front panel. Straightened--as close as I could get it--the tuning shaft.

    I've already benefitted a lot from the many threads on this particular model. It's also nice to have a recap list at hand. Thanks AK!

    Before I get there, though, I have two questions:
    • What's the best way to access the various boards to recap them? I started imagining it while looking at the interior, just to mentally map things out a bit, and I wonder about the easiest way to do it. Seems like I'm on a pretty well traveled path here, so I thought that people might have some tips.
    • Is my only source for a selector switch a donor unit (or a part taken from one)?
     
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  3. zebulon1

    zebulon1 Building a new bench. Finally! Subscriber

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  4. Watthour

    Watthour Electron Rancher - JS3600

    The glass with a hole should be around $20-25, and most local glass shops can do it within a few days, depending upon workload.

    The SX-#50 series knob should be around $10-15 from some of those popular on-line places.

    The shaft is a different story, and as Zeb pointed out, it just might straighten. Aluminum begins to anneal at about 700°F in some of its alloys. Remarkably, that's pretty close to the temperature of some soldering equipment, and heating to that level might make it respond to pressure a little better and not just tear/crack away - Provided the metal is moved gradually.
     
  5. watt

    watt no on

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    Thanks, Zeb, for pointing me to that post. It's a really creative solution. After doing a search, I found a thread in which RS Steve drilled and tapped a hole to accept a screw that he taped up to accept a knob. I might give that a shot.
     
  6. watt

    watt no on

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    I've used a glass place near here for windshield repairs and noticed that they do other small jobs as well. I'll give them a try for the glass.

    Unfortunately, even going slowly with the selector switch snapped off what was left. Whatever did the damage originally took off half of the shaft, so there wasn't much to work with. Hey, if no donor switch materializes (and the tapping solution doesn't work), maybe I'll just set it to Aux and forget it. :)
     

     

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  7. Aaron99

    Aaron99 AK Subscriber Subscriber

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    I can help. PM me.
     
  8. watt

    watt no on

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    Thanks! PMed.
     
  9. watt

    watt no on

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    Bookmarking for reference. This thread has some good detail on an SX-650 restoration.
     
  10. watt

    watt no on

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    Minor update: I tapped the existing selector switch and filed some notches in a cap head socket screw. Those notches grab the plastic knob insert. It works well enough, especially since I don't anticipate switching sources frequently.

    Also cut some Lexan that I have on hand in lieu of glass. Figured that if I don't like the Lexan after awhile, I can detach and take it to the glass place as a pattern.

    Next up: order some caps. And eventually start in on my first veneer job.

    IMG_1611.JPG
     
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  11. watt

    watt no on

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    I've read in other SX 650 threads that it's possible to replace most components without removing the boards completely.

    Has anyone done it that way? I'd like not dealing with the wire wrap if I don't have to.
     

     

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  12. Bruno Primas

    Bruno Primas Active Member

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    It's been awhile, but I believe that the amp and power supply boards can be unscrewed and by unwrapping the wire ties, you can get to both sides of the boards. I think the other boards I accessed from the bottom and there might be a few that the faceplate needs to be removed.

    While you're in there, look at past threads about replacing the troublesome 2SA725/6 and 2SC1312/3 transistors.
     
  13. watt

    watt no on

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    Thanks for that. Noted re: the transistors.

    The parts list in this thread recommends Mouser part 647-UKL1H010KDDANATD as a replacement for C1 and C2 on the Power Amp 1 board. But in my cart, that cap shows a minimum order of 2000. It's a 1 uF 50V cap, 10% with a 105C rating. How important is it to hit that tolerance level and temp rating? I haven't been able to find a replacement with all of those characteristics.
     
    Last edited: Jan 21, 2019
  14. Bruno Primas

    Bruno Primas Active Member

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    I haven't looked but I know that the lower value caps were starting to get phased out. If you go into the Mouser website and look at 1uf 50v or 63v 105°c caps you might find something that would replace the one in the other thread.

    Question for anyone in the know.....

    Is it ok to use a film cap of the same value, (or higher voltage rating), in the power supply?

    If it is, it would probably be easier to find a replacement.
     
  15. Watthour

    Watthour Electron Rancher - JS3600

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  16. Bruno Primas

    Bruno Primas Active Member

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  17. Watthour

    Watthour Electron Rancher - JS3600

    If you read through that linked thread, you will find that the film caps in the tone circuit caused "pops" when the tone controls were switched in and out, so be careful where you place them. Embedded within an audio path near an amplification stage is probably ideal, but where exposed to switching could be a problem. There were several SX-950 and 1050 rebuild threads a while ago with mysterious popping after recap, and this could be another case where they do not belong.
     
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  18. watt

    watt no on

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    Thanks for the responses. I'll steer clear of film caps as replacements.

    About that particular cap (647-UKL1H010KDDANATD), maybe it would be more to the point to ask: how important is the 10% tolerance? There are plenty of other 1uF 105C choices, but I'm having difficulty finding one that also meets the 10% criterion.
     
    Last edited: Jan 21, 2019
  19. Watthour

    Watthour Electron Rancher - JS3600

    There is nothing wrong with film caps in the proper locations. A stacked film would probably work just fine in the C1/C2 positions if it weren't for all the source and tone switches stacked right up next to it.

    If you're leaning toward electrolytic, I'll go out on a limb here and guess that if you knew all the details of the initial circuit design, the inductance in the circuit, the center of the range of frequencies that the cap is supposed to pass, and knew all of the presumptions that were made regarding operating condition variables when the circuit was designed, and then performed all the calculations on that basis, you would discover that the ideal capacitance would be some random value like 0.712 µF, or 1.126 µF, or something obscure like that. Either of those are out of the 10% tolerance for a 1µF or very close to it, so the ±10% would make ANY 1µF cap out of the ideal value range. Since caps, like many other passive components, are only offered in common values, such as 10, 15, 22, 33, 47, 56, 68, 82 (and their multiples), the designers simply chose the value closest to the design point. If it were THAT critical there would be a high-precision device there, like the few instances where you might find a 1% resistor.

    I would suggest getting a 1µF with at least 25V (higher would be just fine) and a low tolerance. Apparently, you are shopping at M-Mart (indicated by the part numbers) so something like this might work out: https://www.mouser.com/ProductDetail/Nichicon/UKL1H010KDDANA?qs=sGAEpiMZZMtZ1n0r9vR22RPm77sS3Lwxh6lVuNgK8LE=

    It isn't an "audio grade" rated cap, but is probably better than the original cap was when it was new.
     
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  20. watt

    watt no on

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    Thanks for that explanation. I appreciate it.

    Looks like I'll be placing an order for the components. I'll report back when I blow something up! :)
     

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