Sx-727 FM causing protection

Discussion in 'Pioneer Audio' started by slayer44, Jan 30, 2017.

  1. slayer44

    slayer44 AK Subscriber Subscriber

    Messages:
    851
    Location:
    Bethel, Vermont
    Hi all...back again. Does anyone have a reasaon why my 727 only goes into protection in FM mode? All other modes perfect. Jammed slayer for 3 hours in aux mode. And phono was good for two albums. Outputs not even hot, but as soon as fm switched, goes into protection. Comes back on in a few seconds, then back off, rinse and repeat. Any ideas?...Thanks!
     
  2. markthefixer

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

    Messages:
    20,626
    Location:
    Bensenville,Illinois
    the output coupling caps c?? and C66 are 2.2uf 16v CSSA caps, the dreaded "capsistors" that are a guaranteed short circuit sometime. They leak electrically and allow DC through, eventually turning into short circuits.
    They are the sky blue Sanyo caps near the corner of the awe-0125 am/fm unit board that has pins 1(left) and 3(right) near it. One is right next to pin 27, the other is kind of between pins 26 and 28.

    DC is probably getting out of the tuner and causing a heck of an infrasonic thump, which the protect circuit triggers on.

    Get rid of all those sky blue sanyo caps, they are pure trouble.

    The guys can fill you in further and recommend a part number(s)....


    and a hi ho Pioneer silver away!!!! (who was that massed man???)
     
  3. slayer44

    slayer44 AK Subscriber Subscriber

    Messages:
    851
    Location:
    Bethel, Vermont
    FYI, already rebuilt the power supply and protect board and voltages at pins are within spec. Still searching through AK's enormous database for this particular problem. I am tempted to believe a problem with the AF unit itself.
     
  4. slayer44

    slayer44 AK Subscriber Subscriber

    Messages:
    851
    Location:
    Bethel, Vermont
    Hi Mark...you must have read my mind!...nothing has been done to the AF board. That makes sense. Would these caps also cause the signal strength meter to not function?...it works in AM just fine.
     
  5. slayer44

    slayer44 AK Subscriber Subscriber

    Messages:
    851
    Location:
    Bethel, Vermont
    Mark...do you mean these?...looks like there are more than two "problem child" caps on this board. I am just going to replace them all. But I will replace the two sanyo's first to see if protection stays off.Thanks for your help.
     

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  6. slayer44

    slayer44 AK Subscriber Subscriber

    Messages:
    851
    Location:
    Bethel, Vermont
    Just wanted to follow up with this symptom to help out others. Turns out the sanyo cap wasn't the culprit. I had a bad driver on the amp board so the idle/offset was out a hair. Why this would effect FM only is beyond me, but it fixed the voltage going into the tuner board. Now I am picking up stations in my basement with rabbit ears. I had to replace the left side transistor SA814 to fix the problem, so I replaced all with 2073/940 combo and now good to go. I am going from memory here, so if I made an error, feel free to correct me. Slowly learning alot about these X2X units. Thanks all for your help.

    EDIT...The drivers were 2SA647/2SC1157. Tired drivers were not allowing tolerable idle/offset. The SA814 I mentioned previously applied to my SA-8500 restoration...don't trust your memory when working on five things simultaneously!...:eek:
     
    Last edited: Mar 20, 2017

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