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Pioneer SX-636.....rushing sound on left channel

Discussion in 'Pioneer Audio' started by BmWr75, Apr 28, 2013.

  1. markthefixer

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

    Messages:
    21,110
    Location:
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    are you sure they are 726's? they list 2sc945's for stereo on/off control and 2sc763's for audio amp after stereo decoder chip. look at the numbers carefully.
     

     

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  2. BmWr75

    BmWr75 Addicted Member

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    5,266
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    I was wrong, there are two 725 transistors on the Tuner board, not 726s. Here's a picture showing one of them.

    [​IMG]
     

    Attached Files:

  3. markthefixer

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

    Messages:
    21,110
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    a992's...
     
  4. BmWr75

    BmWr75 Addicted Member

    Messages:
    5,266
    Location:
    Northeast MS
    Got it....that is what I ordered to replace the A725s.

    Power amp adjustment question. Page 18 of the service manual talks about measuring the DC voltage across the power transistor pairs. It specifies to use an 8 ohm dummy load across the speaker terminals while doing this measurement/adjustment. I don't have an 8 ohm dummy load. The speakers on my bench measure 3.5 ohms.

    I did the measurement and read 28.5 mV left and 32.4 mV right. The manual says it should be 20.0 mV. Is using my speakers as the dummy load affecting these measurements?

    Also measured DC offset now at the speaker terminals. Don't think this is adjustable on the SX-636, it is not mentioned in the manual anyway. DC offset is 17.3 mV left and 22.3 mV right.
     
  5. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
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    Location:
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    I've never connected dummy loads to any X3X series receiver when doing the adjustments, per past practice on various units postings per Mark. Having said that tho, I've never seen a posting on the 636. It's similar in practice to the 434 and 535, that it's probably ok to not have dummy loads connected.

    No DC OFFSET adjustment. Just the BIAS. Set for AUX, Zero Volume, No input connected. Take off the speakers and leave the terminals free. Set for 20mv.

    Offset is fine. Anything below 50mv is very good. It may even come down once the bias is set.

    Larry
     
  6. markthefixer

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

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    look for an output coupling cap, if there is one (it will be almost as honking big as the power filter cap, and there will be one per channel), then a 10 meg DMM will give you strange and frightening DC offset readings that will "disappear" with a speaker load. It's the electronic leakage current that's unavoidable through a capacitor. The DMM is sensitive enough to detect it. But there isn't enough of it to disturb a speaker, no less start a fire. (unless of course the capacitor shorts out - then ouch, THAT's what fuses are for)

    If there IS NO output cap (I don't have a handy dandy model list for that right now) a load resistor is not needed to set DC OFFSET, the dc offset will be the same with it or not. The Idle current may have a slight difference with a load resistor in place as now there is some place for the current to sneak off to rather then go through BOTH push pull output transistors.
     
    Last edited: May 14, 2013

     

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  7. BmWr75

    BmWr75 Addicted Member

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    Thanks again Mark and Larry. Your help and guidance is much appreciated.

    Refurb done.....she is singing like brand new!!!
     
    Last edited: May 14, 2013
  8. BmWr75

    BmWr75 Addicted Member

    Messages:
    5,266
    Location:
    Northeast MS
    Last two caps redone. Fuse lamps replaced. Wood case Feed-n-Waxed. I'm done.

    [​IMG]

    [​IMG]

    [​IMG]
     

    Attached Files:

  9. Alienz

    Alienz Super Member

    Messages:
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    Great job! :tresbon:
     
  10. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
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    Location:
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    OOO-RAH!!!! Great Job! She looks brand new.

    I just read the last of it from my last post. checking the schematic, No output coupling cap. No Protection board or relay. So those two honkin 4A fuses are your ONLY speaker protection. But if it's anything like my 434, it's a great little receiver.

    Larry
     
  11. markthefixer

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

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    I blew it on the list, the awh-034 diff amp input stage transistors are now correct.

    anal cranial insertion err..... pnp - npn inversion ... now fixed...
     

     

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  12. audiojones

    audiojones Jonesin' for audio Subscriber

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    SX-636 power supply board AWR-060 B cap value change

    Just a heads up to anyone recapping an SX-636 - You may find that C12 on your power supply board is actually 10uf 16v instead of 220uf 16v. It appears that this was done at the factory and should be kept as a 10uf if that's what was in there originally. My power supply board number was AWR-060 B so I don't know if the non-B version uses a 220uf or not. The schematic for the non-B version appears to match up with the AWR-060 B board except for the value of C12. Here's a thread about the issue.
     
    Last edited: Apr 26, 2015
    dlucy likes this.
  13. Young46

    Young46 Active Member

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  14. zebulon1

    zebulon1 Building a new bench. Finally! Subscriber

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  15. markthefixer

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

    Messages:
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    Location:
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    I'm adding one more post to this, don't have a part number yet, but the SX-636 main caps do not have bleeder resistors, they depend upon idle current to deplete them, BUT idle current goes away during shutdown when the regulated DC disappears and these caps stay charged for a long long time - I just remembered that.

    So add bleeders, say 3k ohms at 1 watt (35v into 3000 ohms is ~ 0.4 W) across the two main caps 6800 uf 35v.

    This is important because the output is DC coupled (no output cap) and there is no protection relay. I remember times when I shut off my SX-636 and a while later there were scratching and rumbling sounds coming from my speakers (the 2sc1451's were probably clearing their throats) so I used to turn OFF the speaker switches before turning off the power.
     
  16. zebulon1

    zebulon1 Building a new bench. Finally! Subscriber

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    Hey
    Could you add the recommendation to the post on page one?
    I often wonder about that very issue.
    Some use caps (like the 1250) and others use resistors like the 1010's.
    This is an example of the posts (of yours) I miss most.
    Is the hiatus over?
     

     

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  17. markthefixer

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

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    Hiatus not over yet :(

    I do overwatch for for bad things as much as I can, but there's a huge time difference between reading and posting.
    Thus the quick post above as the recollection hit. No post backtracking, parts lookup etc.
    sorry. :dunno:

    eventually I will be doing MY SX-636, so the thread will eventually be revisited. But that's a long long time off.
     
  18. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,102
    Location:
    Dallas, TX
    I have a SX-636 on the bench. Working on the AF Amp AWK-035-0 (Tone Controls) and using markthefixers list in post #6 as a rough guide. Just wanted to point out that my unit has the orange jacket CEANL caps at 13/14 and 21-24 for the 4.7uf 25v stock caps. Therefore I'd recommend using ukl caps over the upw as in the list.

    Edit: The stock Caps 9/10 100uf 16v on this same board are the yellow jacketed CE LL caps by Nippon Chemicon and are also low leak types so use ukl here as well.
     
    Last edited: Feb 1, 2017
  19. dukeofurl

    dukeofurl AK Subscriber Subscriber

    Messages:
    153
    Location:
    California via Yorkshire
    Going through the BOM list, I've found that:
    Mouser #: 667-ECQ-E1474KF
    Mfr. #: ECQ-E1474KF
    Mfr.: Panasonic
    Desc.: Film Capacitors 100DC 0.47uF 10% L/S =7.5mm
    (x4)
    ....and
    Mouser #: 598-DSF050J334
    Mfr. #: DSF050J334
    Mfr.: Cornell Dubilier
    Desc.: Film Capacitors .33UF 50V 5%
    (x2)

    ......are no longer available.
    Any suggestions for Mouser part number equivalents?
    Thanks in advanced!
     
  20. dukeofurl

    dukeofurl AK Subscriber Subscriber

    Messages:
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    Location:
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    Sorry if this is the wrong place to ask the above question but this thread is where I discovered the BOM list for this model.
    If so, please have my posts deleted.
     

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