sx-939 static

Discussion in 'Pioneer Audio' started by kcmoejoe, Oct 28, 2009.

  1. montecarlossfan

    montecarlossfan Active Member

    Messages:
    477
    Location:
    Canton,CT
    I'm currently redoing a 939 that kind of does the same thing ..it makes a sharp click/pop occasionally. I got it for a great deal and it is in immaculate condition so I want to keep it and rebuild it. I knew about this issue and the funny thing is after it sat for a while since the previous owner didnt use it..it never made any noises until i used it for 2-3 days. I will keep you updated when i trace down that pesky lil bugger just to see where in the preamp chain it is coming from...that is if i can catch it in the act.
     

     

    Please register to disable this ad.

  2. markthefixer

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

    Messages:
    21,030
    Location:
    Bensenville,Illinois
    kcmoejoe check the 13v power supply, and yeah, put the c1845's in...

    montecarlossfan, separate the pre/power to test or do all the 725/726's as well as the c1451 or any other transistor that LOOKS like the c1451 in the amp and is an a8??...
     
  3. montecarlossfan

    montecarlossfan Active Member

    Messages:
    477
    Location:
    Canton,CT
    I narrowed it to preamp right away..doesnt seem to be tone controls etc whether or not they are on or off it is still there...I will find it..I'm gonna put a scope on various sections just for haha's and see where it is coming from...I have yet to dig deeper as I am putting together a cap list/restoration sheet with all relevant part #'s to help out future AKers on the 939..I figure I have the knowledge to do so, and it will help alot of people out..As always Mark you and Glenn have been the stereo Gods to many on here. I figure as 3rd year EE student you can never learn enough.
    I'm also going to put another relay in there for powerup to take the load off the power switch...I have never seen a dead switch but considering this unit it made it this far in life..it wont hurt...As well as an LED conversion using white led's with a current limiting resistor and ends of glass fuses to make bulbs..it will be interesting to see the outcome.
     
    Last edited: Apr 19, 2011
  4. markthefixer

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

    Messages:
    21,030
    Location:
    Bensenville,Illinois
    search on "vanity led" in ebay...
     
  5. montecarlossfan

    montecarlossfan Active Member

    Messages:
    477
    Location:
    Canton,CT
    I was lookin at those...curious as to how the dispersion of the led is.
     
  6. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    Ok...so Mark, I opened it back up and replaced all the transitors with c1845's on the control amp board but didn't have alot of time so ignored replacing all the caps for the time being and it took care of my static I was getting. :thmbsp:

    But now something has me wondering :scratch2: playing CD's through the AUX input sounded really thin and loud (hot) to me, read somewhere that CD players can put out 2v which could be a bit too hot for vintage receivers, so I put a -20db attenuator inline and it helped alot but still sounded thin (not much bass) so messing around I flipped the duplicate switch to "On" position and viola...much more fullness and rich bass.

    What does this mean? I have no problem keeping it switched "on". Even the FM sounded better...which I thought before sounded kinda hot and slightly distorted.

    I'm happy at this point, but if this means I still have a problem, I'm game to get back in there and do more.
     

     

    Please register to disable this ad.

  7. markthefixer

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

    Messages:
    21,030
    Location:
    Bensenville,Illinois
    classic dirty switches...
     
  8. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    NEW PROBLEM:
    So, after 7 years of my 939 running flawlessly. I now have the dreaded static / crackle / pop back, but only in the right channel on AUX. pressing mono in you can hear it in both channels. balance just isolates it to right, quiet to the far left. Pulling metal jumpers makes it go away (silent).

    Volume gain will make it louder and with no volume it's silent. I've opened it back up this weekend and been using deoxit on all the switches and pots many times. Going back in this post, I believe the only thing not changed was some old caps/transistors on the power supply. my final post #86 above it looks like my static i was having was remedied by putting in new 1845 transistors. Except, that static was also in the phono not just Aux, and turning the volume down to 0 didn't get rid of it like I can now with it just in the Aux.

    So...I'm wondering if this isn't in the preamp cont. board? could those transistors have gone bad over the last 7 years?
     
    Last edited: May 30, 2018
  9. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    list of parts replaced 7 years ago:

    amp board (awh-030)
    Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, Q12
    C1, C2, C3, C4, C5, C6, C11, C12

    protection board (awm-062)
    Q1, Q2, Q3, Q4, Q5, Q6, Q7
    C1, C2, C3, C4, C5, C6
    1n4004 diode across pins 9 and 10

    control amp bd (awg-027)
    Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8
    all the e-caps **replaced 5/28/18**
    all the mylar caps **replaced 6/4/18**

    EQ - Phono board (AWF-013)
    Q1, Q2, Q3, Q4
    Q5, Q6, Q7, Q8
    and all the e-caps

    nothing done to the tuner bd.
    I believe Q3 is the only thing done on PS bd.
     
    Last edited: Jun 16, 2018
  10. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,763
    Location:
    Glen Burnie Md.
    There are a couple of those Green Mylar caps(kludge caps in that position) and SkyBlue lytics around the tone controls that if you haven't changed them, do so. If you can fit Mylars in place of the lytics, you'll save yourself the trouble of replacing them in the future. Cornell Dublier DME series is a good cap for these areas as they are quite small. Also replace what caps you haven't replaced on the other boards. If you have access to Canned Air, you can "cool" transistors when you have the staticy sound. Just a light blast on each at a time, letting the cooled one to heat back up. A transistor that is acting up will more often than not straighten out when cooled and then act up as it heats up.
     
  11. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    Thanks Larry, I did run a test to narrow it down (please correct me if I'm wrong) I hooked up a separate amp to the Pre-outs and the noise is still there on the right channel. Also, ran MP3 player into Main In and it was quiet...So, that means it's got to be in the pre-amp control board, correct? I see 8 of those green mylar caps, will need to figure out part # for mouser. I've also replaced all the sky blue lytics. I freeze sprayed the trans but no change, the noise is there from cold turn on everytime.

    The ones circled in red are the mylars caps I should try changing next? also what about the small blue circled ones?
     
    Last edited: Jun 2, 2018

     

    Please register to disable this ad.

  12. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,763
    Location:
    Glen Burnie Md.
    The blue circled one's are ceramics, leave them as they rarely if ever go bad. Let me take a look at the schematic for the control board and figure out the caps these caps, C17 thru C20 and C37 (0.056uf 50v) should be replaced. These are all in the front end of the board around the front of the switch groups. These were the troubleprone caps on my control board. Make absolutely sure the switches and pots are clean. Run it with the tone control bypass in OFF and see if it still is staticy.

    These are the only .056uf caps I could find on mouser @ 50V. Next step up was 250v which wou;d be too big. Lead spacing is 5mm. Should be ok.
    https://www.mouser.com/ProductDetai...=sGAEpiMZZMv1cc3ydrPrF17gIuUB4mH16sG/YC/ox6k=
     
  13. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    Ok, will order these to replace C17-C20. C37 is 0.0022 I imagine that is fine since the value is higher? I'm almost certain I've soaked the switches enough, the sound has never improved spraying and working every switch. And with tone switch in bypass the static w/ occasional pops are still there.
     
  14. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,763
    Location:
    Glen Burnie Md.
    No the C37 should be .0022+or - 10% or less. as it's a 50V I wouldn't go more than 100v. Mouser has no .0022 in a radial or axial unless you go with a 630v piece which is way too high for voltage.

    Try AES or Justradios.com one of them should have all of the parts. Try to get the smallest physical size you can as they go inbtwn the switches.
     
  15. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    How about these for C37: https://www.tedss.com/2020048607

    and these for C17-20: https://www.tedss.com/2020048665
     
  16. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,763
    Location:
    Glen Burnie Md.
    Those should be fine.
     

     

    Please register to disable this ad.

  17. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    I replaced all the green mylar caps, but no change, still have the right channel static that only 0 volume and far to the left balance gets rid of it.

    Also, when i hook up a set of RCA's from the pre amp LEFT to the amp input RIGHT and from the pre-amp RIGHT to the amp input LEFT the static noise switches from right channel to the left channel. What would this point to?
     
    Last edited: Jun 7, 2018
  18. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,763
    Location:
    Glen Burnie Md.
    That the problem is before the amp in the Right Channel. Get a can of canned air. Turn on the 939, and let it warm up so it starts the static. You are going to hit each transistor housing on the boards (tone control, preamp and EQ board) with the canned air (but turn it upside down so you get the liquid). a SHORT SPURT will cool down the transistor. If a transistor is causing the problems due to heat stress, then cooling it down will stop the problem, until it heats up again. When the static stops, wait for it to warm up and do it again on that transistor. You want to verify it. Mark it with a white marker or liquid tape. Then replace that transistor. Do all of them on all the boards. replace any that show signs of correction with the freeze spray. The most likely suspects are 2sa725's, 2sa726's, 2sc1312,2sc1313, 2sc1384's in that order.
     
  19. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    Ok, there is no need to let it warm up, the static is there as soon as I turn it on. I will grab some more canned air. I went ahead and replaced the transistors on the control bd and EQ/phono with 1845's and 992's. Am I correct the preamp IS the control board?
     
    Last edited: Jun 8, 2018
  20. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,763
    Location:
    Glen Burnie Md.
    Yeah the Control Amp is the "preamp". But before you do anything with the transistors, Double check every GROUND on the unit from the inputs, all the way thru the amp. Plus grounding on the Mic bd, and the PWR Supply. Clean up any corrosion on the chassis connections and make sure you get less than 1.0 ohms on each one. The instant "on" of the static leads me to believe it's possibly a grounding issue.
     

Share This Page