SX-9930 rebuild and some general questions

Discussion in 'Pioneer Audio' started by kdschmidt, Aug 6, 2017.

  1. kdschmidt

    kdschmidt New Member

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    Wasn't sure which forum was most appropriate for this. Since I'm about to try and refurbish an SX-9930 (939) I thought the Pioneer forum might be best.

    I picked it up at a yard sale. It's in amazing shape and I want to keep it for my main personal set. I was told it stopped working after a lightning strike. I replaced a visibly blown cap (C1 on the chassis) and it fired up and works great, but when using a turntable it definitely needs new transistors on the EQ board and I'd like to recap-refurb the entire unit (in stages). I want to do as thorough a job as I have the capacity to do (lacking any specialized test equipment beyond a multimeter).

    I have some questions regarding audio repair that I hope some knowledgeable folks might answer for me. First, I have a bit of experience soldering and re-capping and have been inside many pieces of electronic and audio equipment and (?)successfully repaired them. Though, I have little knowledge of such circuitry. I do it through trial and error, observation and I guess a lot of luck :)

    So, some of these questions may be embarrassingly basic and others may be more technical.

    Should all transistors be replaced, or just those that have historically been identified as problematic/potentially problematic?

    • Same with the caps, should all the electrolytic caps be replaced? I understand the main filter caps rarely need replacing, true? Any other types of caps or board positions replaced as precaution?

    • I've read here that the replacement caps should be a higher voltage than the originals. Is that STRONGLY suggested or is it okay to replace with ones of the same voltage? If so, how much higher? (I do understand about replacing with Audio Grade, low noise-high gain caps).

    I've been careful and haven't ever had a problem, but how long does it take a capacitor to safely discharge? I've heard mention of ranges from about 15 seconds to 15 minutes. I do understand it would vary depending on various factors, but any general rules of thumb?

    Lastly, for right now :) Are there any tricks, suggestions, or recommendations for swapping out boards on Pioneers with twisted-wire pins? I bought a few boards to more easily rework on the bench, but when starting to swap with the board in the unit, discovered that neatly pulling those pins isn't as convenient as I expected it to be :)



    Thanks for any help or answers!!
     
  2. Bassblaster

    Bassblaster Super Member

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    Im not an expert by any means but i can help get you started. (i have an SX-636 :p)

    There's no need to replace all transistors other than the known ones like,
    2SA725/726 Shot noise, which is the pops and crackles you can hear. often in failing phono stages. Replace with KSA992 hFE matched.
    and the most important of all, the infamous 2SC1451, Static bursts and open circuit faults. If this little gem fails expect to rebuild the entire power amp on that channel. Replace with KSC3503

    These units are almost 45 years old, its generally a good idea to just replace the small electrolytics and sometimes the filters. ceramics are often good alone with film types. ive seen people say the "blue drop" tantalum caps can be trouble too.

    Replacing caps with a higher voltage is not needed unless there normal operating voltage is close to the limit. example the SX-636 has 35V filters but runs on 31V. thats a bit close and most will choose to up that voltage.
    Other than supply rails caps in an AUDIO parts will at most see about a volt or so.

    The only caps you need to worry about discharging would be the main filters but most of them will discharge to a couple volts or so within seconds of power off

    Twisted wire pins, fairly easy. DO NOT UN WRAP THE WIRE! IT WILL BREAK. Just un-solder the pin from the PCB. Boom done.

    EDIT: Forgot that the blue Sanyo caps in the tuner are known to short. so replace all of those.
     
    Last edited: Aug 6, 2017
  3. rkgren1

    rkgren1 AK Subscriber Subscriber

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    Good advice from Bassblaster.
    Especially since you have had lightning damage, it is prudent to evaluate the power supply board first.
    Check all output voltages against specs.
    Consider rebuilding that board first.

    Many people do not replace filter caps because new ones of the same diameter and length are very expensive.
    As long as you are not a stickler about the size of the replacements, they can be replaced with new at reasonable cost.
     
  4. kdschmidt

    kdschmidt New Member

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    Hi, thanks for the replies!
    Upon making a parts list, a few more questions arise.
    I see that many caps are close or virtually the same on different boards. I have read that Audio quality Caps are necessary for the EQ amp, Power amp, Tuner Board and Control Amp (I believe the Muting Circuit as well), is it okay to use the same type of caps on the Power Supply Board and Protection Circuit?
    Second, there are caps which are close in voltage with the same capacitance, for example, on the Power supply, it calls for a 47uf 63v and 2x 47uf 50v. Is it okay to just order 3x 47uf 63v ? Similarly, 100uf 16v on one board, 100uf 10v on another and 100uf 25v on yet another. 100uf 25v for all?
     
  5. john stumpf

    john stumpf AK Subscriber Subscriber

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    on this forum search "sx-939 recap list" you will find an old list that also has the transistor replacements. ive done a 939 and a 1010. any electrolytic 1 mfd and below should be replaced by a film cap. depending on the luck of the draw, its quite possible that some of the capacitors dont match the list there wont be many but its a possibility. if the set works well now and appears un molested replace with WHATS ON THE BOARD WITH A LIKE VALUE. so if you want all the correct parts at one go you will have to check the value of EVERY CAP and bounce it against the list. replace the bias and offset var,resistors with bournes items . as to your previous query about the 16.10.25 volt caps yes you can sub all with a higher value, baseblaster is correct about the transistors which leads you to another search, just google searches outside the forum like this "pioneer problem transistors, audio karma" its well worth your time.
     
  6. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Audio caps are NOT needed on these units. They run perfectly well with Nichicon UPW/UHE series for the power supplies, and the UKL series ELECTROLYTICS for mainly everything else that is electrolytic. CSSA type caps are Solid Aluminun capsistors (capacitors that eventually become resistive and hence no good.) There is a 9930 thread here that was done last year that should have 9930 specific cap lists (it's slightly different than the 939) but I can't find it under 9930 and 939! If nothing else use the 939 list thats linked from this thread http://audiokarma.org/forums/index.php?threads/pioneer-recap-lists-sticky-suggestion.457663/ This list was made and has been vetted by MARK THE FIXER (#1 GURU TECH on PIONEER who's been doing this for 30+ years now. 99% of the lists on AK PIONEER started with MARK) Some of the parts might now be obsolete, so make up a list from that, check it against the Mouser catalog, and note any that are obsolete so we can update it. Once it has been checked and vetted by US, THEN and ONLY THEN order the list. Also note any differences from the list and the actual unit! This is very important as PIONEER made unpublished changes after the Service Manual/schematic were published.

    Transistors get replaced as noted on the list. Transistors as noted above in prior posts are included in this list. AT MINIMUM change the 2sc1451's on the Main Amps, and any 2sa725 or 726. You'll note in the parts list in the manual for each board that some transistors have subs. In the case of the 2sa725 and 726, this will be a 2sa763. If any place you find a 763, leave it as it's NOT A PROBLEM CHILD! However having said that, if you feel froggy and want to go ahead and change it, it won't hurt to do so.

    I like mine a whole lot better than my old SX-1010. Better mids, and highs, the lows are a slight bit diminished, but not overtly so. Total watts are lower than the 1010, but I think this enhances the 939/9930.

    DO NOT UNWRAP a Wire Wrap connection. When it's wrapped around the post it's stretched slightly which allows the pin to cut into the wire and get an anerobic connection 4x each rotation. Better than solder and will hold up under extreme vibration. Un-Solder The pin and check for a splayed end. If splayed, grip the end and squeeze the end until straight THEN pull the pin. LAST RESORT is to clip off the wire at the insulation, then strip 1" being very careful about nicking the wire when stripping. Then cut off 1/2" and use the rest for wrapping around the pin and soldering.

    The SX-1010 and the 939 used some of the same boards. Tone control boards and protection circuit come to mind. Board Numbers are rubber stamped in the corners. You can use a newer SX-1010 parts list on certain board for the 9930 provided the board numbers are the same. Check it out.
     
    Last edited: Aug 7, 2017
  7. kdschmidt

    kdschmidt New Member

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    Hi all, thanks again,
    I think John S and Larry are referring to the same list. I have read that thread and copied that list. I made a list for myself as well from a 939 manual with replacements garnished from many threads here. I'll need to check those lists against each other as well as the set itself. I'll post my final list in a few days. I'll need to learn a little more about some parts and procedures mentioned. I just re-did the EQ amp on my SX-535 to get some practice (the sa726s were causing the phono to cut out. It worked out very well).
    Larry, I've read lots of stuff here from you, MTF and many others. Now, please dont get me wrong, but as I've come to understand it, some audio circuits require caps with different attributes such as low noise, high gain, etc., particularly caps in the audio path. I think I even recall MTF, maybe it was in that 939 thread, to pay attention to cap types spec'd on some audio boards (ie; CEA vs CEANL). NL meaning low noise ( so, CEANL being tantamount to Audio Grade, correct??). I read a thread that even the Power Suppy board should be treated as being in the audio path. I'm guessing you might not agree with that, but ultimately, it wouldn't hurt to use audio grade caps all over, would it?
     
  8. Bassblaster

    Bassblaster Super Member

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    Would it hurt to use audio caps all over? No. would it be the best it can be? No. the reason people suggest Nichicon PW or Panasonic FC caps for powersupply stuff is that that series have low ESR making them better for jobs with ripple.
    High gain and low noise refer to transistors/opamps. capacitors dont have any gain or noise spec. they are a passive.
     
  9. kdschmidt

    kdschmidt New Member

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    Hmmm, I swear I remember reading somewhere here that The NL in CEANL type caps represented "low noise". I scoured all the threads on the subject I had saved from here at AK and elsewhere but couldn't find the reference. I looked through the Tuning Fork Cap issues and see that the NL refers to caps designed for a very low leakage current. In the 939 manual, most all the caps on the EQ Amp board are spec'd as CEANL. I assumed that had implications of caps that were "Audio Grade".
    So then, what makes a capacitor "audio grade" and how can one tell by looking at the cap or its printed info?
    On a side note, is there a thorough list of audio acronyms anywhere?
     
  10. kdschmidt

    kdschmidt New Member

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    I hope you guys don't think I'm being unreceptive, blockheaded or even disrepectful. I'm paying attention, I promise. And I want to learn, correctly.
    I've read a lot on the discussion boards and, unfortunately I guess, I've picked up the distinct impression that "Audio Grade" caps (parts) are a must for any rework in the direct audio path of a system. It's also something that seems to make sense, though it apparently is counter intuitive to your indisputable experience, expertise and success.
    I do now understand I had my own wires crossed apparently with the "low noise" attribute for caps (I wrongly thought NL=low noise=audio grade).
    They are called for (CEANL), at least on the EQ Amp, and a few on the Control Amp.
    So, if the NL attribute doesn't really make for an audio grade cap, what does constitutes an "audio grade" capacitor?
    And why are they unnecessary (or undesirable) in these old Pioneer receivers? Don't they add any value?
    Just trying to understand before I proceed.
     
  11. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Nichicon UKL's are low leakage caps as already suggested and are the ideal replacement for the original Pioneer CEANL and CSSA low leakage types. If the value of the original cap is small enough replacing with a film cap is even better. You can replace all of the other ordinary caps in the unit with audio grade if you so choose but Nichicon UPW (low impedance) are still a great choice for the power supply as Bassblaster suggested. Remember audio grade caps are NOT low leakage types.
     
  12. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Here's Mark the Fixer's Guide to replacement of caps. He's done Decades of research and this list has stood on it's own (for type) for at least the 9-10 years I've been here and have used it on PIONEER, Sansui, Old FISHER 1st Gen S.S. Each and every one of these units was noisy, and the change was subtle on about 1/2 of them with the rest being on the order of BLACK HOLE QUIET!(Black Hole were the FISHER's, a Sansui, and 1/2 of the PIONEERS)


    Originally Posted by markthefixer

    UPW and UHE from Nichicon is the general purpose e-cap series I usually recommend. Yes, they are 105 degree c caps.
    There are Panasonic caps EchoWars recommends as well, they are fine.

    THEN there are the low leakage caps, which is some circuit locations DO make a difference. They ARE literally QUIETER.
    They are the unique Nichicon UKL series, which was originally just an 85 degree c cap line.
    Now there are UKL's that are 105 degrees c rating.

    When examining the recap lists (especially the ones I personally did) You will find MANY UKL caps in them.

    My "rules of thumb" for caps:


    Rule of thumb: 0.1uf to 1.0uf of any type >> stacked film DSF(cornell dublier) or ECQ (panasonic)caps
    cea >> nichicon upw or uhe caps
    ceb > nichicon tvx axial caps or holler for help on these
    ceanl, cssa, csza >> nichicon UKL caps - (low noise, low electronic leakage)


    It didn't cover non-polarized (or "bi-polar") caps, there are a few, but I can't look up that answer now at this computer about which Nichicon series to use.

    The "stacked film" caps are being discontinued in some convenient voltages, but regular ecq's will do.
    End of Mark the Fixer's quoted post.
     
  13. kdschmidt

    kdschmidt New Member

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    Thank you guys (all who've chimed in) very much. I do intend to proceed as you've recommended. There's a lot I need to learn about the why's and how's of audio circuitry.
    Right now I'm a bit side tracked with other important stuff, but I'll be posting back soon. I think I'll need a little help doing some testing and have some questions about some non-cap/non-trans parts that have been mentioned on the lists.

    Larry, speaking of Fisher, I picked up a very rare 395 at yard sale for $10! It's in fabulous condition and every feature seems to work great including the FM auto-scan. Even all the lights work. Although it sounds pretty good I want to refurb it eventually too.
     
  14. Bassblaster

    Bassblaster Super Member

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    1,648
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    bi-polar caps Nichicon UES is a good choice. looks nice in that bright green too :p
     
  15. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    The 395 would be a Canadian model. As would be the later 505 which is the same basic unit probbly with a higher rated amp (similar to the 250-TX-400T. The only difference is the amp boards). The 450-T is the version sold in the states. They were mid level units from 1969. The 450-T is rated 55wpc 8ohms 1kHz so about 30wpc RMS.

    Up in the STICKIES is a thread referenceing the PIONEER Tuning Fork Service Guides. Download them all. Probably have about 95% of what you're looking for. http://audiokarma.org/forums/index.php?threads/pioneer-tuning-fork-service-guide.249745/
     
  16. kdschmidt

    kdschmidt New Member

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    Thanks for the info on the Fisher! There's not much info on it out there. Thanks everybody, for the other help too. I'm distracted right now with other matters but I'll be back posting shortly when I re-open the SX-9930.
     

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