Pioneer SX-727 Crackle and pop

Discussion in 'Pioneer Audio' started by grindfix, Aug 10, 2017.

  1. grindfix

    grindfix Active Member

    Messages:
    169
    First, let me thank everyone who helped me rebuild my SX-1280. Special thank you Markthefixer for providing BOM and detailed guidance. I got about 4 months of 1-2 hrs/day on it and it performs and sounds awesome. At first, I wasn't impressed, but I knew that all new capacitors need time to break-in. Sound eventually opened-up and I think it still gets better and better every day!

    New project (one of many) is SX-727 with it's common crackle. Cleaned pots, switches and trim pots on Amp board. Set Bias to 20ma/DC to 0mv. Left channel was initially dropping out sounding like cough then eventually cleared. I suspect weak capacitor somewhere. Now it's been playing for several hours and occasionally, there is a crackle. My plan is to rebuild Power Supply and replace all small transistors and e-caps on the Amp board AWH-011.
    I found some old threads with info. Does anyone have current parts list for this receiver?
    Thanks
     
  2. markthefixer

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

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    I haven't done a reverse engineer for the replacement transistors.
    The caps are almost up to date (just checked) , 2 values for a total of 7 caps have gone obsolete or problematic.
    one is 0.47uf film cap
    other is 1uf 50v or greater.
    No time to figure out replacements right now, others probably have. They'll chime in (I hope).
     
  3. larryderouin

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

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    PRELIMINARY!!! DO NOT USE UNTIL VETTED BY MARK!


    Mark; Take your pick. Probably others but I used your guidelines for this.

    0.47uf 50V
    Nichicon... http://www.mouser.com/ProductDetail...=sGAEpiMZZMv1cc3ydrPrF652zNprbYwMkWvn1Y212qE=
    WIMA........ http://www.mouser.com/ProductDetail...=sGAEpiMZZMv1cc3ydrPrF7l45uRd9dVhExePEl6XCE8=

    1uf 50V Film
    Nichicon.... http://www.mouser.com/ProductDetail/Nichicon/UMA1H010MCD2TP/?qs=QB0ovJDgFgtHTr1B4NGuNA==

    1uf 50v Lytics
    Nichicon
    UHE Series... http://www.mouser.com/ProductDetail...=sGAEpiMZZMtZ1n0r9vR22e0BBN1kF1oiuvGryroGz0U=
    UKL Series... http://www.mouser.com/ProductDetail...GAEpiMZZMtZ1n0r9vR22RPm77sS3Lwx%2bcPhT4OlSXQ=

    GRINDFIX: DO NOT USE THIS UNTIL VETTED BY MARK.
     
  4. larryderouin

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

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    grindfix; This is INFO ONLY. Don't order any until Mark Vetts the list. Personally of the two brands, I would go with the Nichicon's in the film types due to longer leads. Most of the WIMA's have very short leads and very often need lead extensions.

    As for the Lytic's, The UHE series would go in the Power Supply Section while the UKL go in the signal path.

    If Mark says go with the Films for everything, then that makes it a lot easier.

    Larry
     
  5. grindfix

    grindfix Active Member

    Messages:
    169
    Mark
    Have you had a chance to look into this?
    Thanks
     
  6. larryderouin

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

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    GRINDFIX; Mark is super busy this time of year, so go with the Nichicon's. I use them in my PIONEER gear (sx-737,939,790 and 434) so they are proven in at least 4 receivers.

    Larry
     
  7. zebulon1

    zebulon1 This summer heat slowed me down. Subscriber

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    Replace the transistors that appear in this post. All others should be fine.
    The Head amp and AF unit probably will be where the noisy transistors lay.
    The AF Unit uses the JEFT's (Q1,Q2) stay clear of them. No current replacements, should be OK.
    It's a shotgun approach to troubleshooting but with a high fix'n probability.

    Top 10 worst 70's transistors.
    Vintage HiFi Transistor Replacement Table

    Type Replacement(s) Failure notes
    --------------- ----------------------------------------------- ------------------------------
    2SA720 KSA1013
    2SA725 KSA992 or BC327 Shot noise
    2SA726 KSA992F or KSA992E or BC327 Shot noise
    2SA798 (2x) BC560B or (2x) KSA992
    2SA809 KSA1381 Poor heat dissipation
    2SC458 2SC2240 or KSC1845F or KSC1845E Leakage, noise, static
    2SC631 KSC1845 (but test for hfe 350+) Prone to failure or noise
    2SC632 KSC1845 (but test for hfe 350+) Prone to failure or noise
    2SC871 KSC1845F or BC550C Leakage, noise, static
    2SC1000 KSC1815Y Leakage, noise, static
    2SC1312 2SC2240 or KSC1845 or BC337
    2SC1313 2SC2240 or KSC1845 or BC337
    2SC1318 KSC2383Y or KSC2690AY Thermal stress, thermal flex
    2SC1344 2SC2240 or KSC1845 Static burst
    2SC1451 KSC3503 Static burst, open circuit faults
     

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