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Pioneer SX-850 Problems

Discussion in 'Electronic Repair' started by davesheb, Apr 16, 2004.

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  1. davesheb

    davesheb Guest

    I have a Pioneer SX-850 receiver. It's a great valuable item and I want to
    repair it. When I turn on the tuner, it plays FM for a few seconds then I
    hear a ping then it kicks out. If I get back to the tuner it plays for a
    few seconds then kicks out again. Does this sound like a relay problem or
    something. Also some of my switches don't make contact. I've tried to
    take it apart to try to clean or stretch some springs to make better
    contact but it is difficult. Are the switches available for replacement?
    Any help anyone can give would be appreciated. Thanks.
  2. Sofie

    Sofie Guest

    When the FM "kicks out" does the amplifier section of the receiver still
    work with other audio sources OK?
    If the problem is really in the amplifier section and not the FM Tuner
    circuitry then more than likely the protection relay is energizing, thus the
    "ping" you hear.... probably caused by faulty components or dry, cracked
    solder connections in the power output and/or driver circuitry.
  3. The "ping" you hear is the speaker relay cutting out. On the SX-850 this is
    usually caused by a single bad transistor in the power supply, though there
    are certainly other power supply issues which can trigger the protection
    circuit to cut off the relay.

    Cleaning or stretching springs won't make dirty controls work. There are
    cleaner / lubricants designed for the purpose, and they need to be used with
    an understanding of how the switches and controls are built and how they do
    what they do.
    One uses a cleaner / lubricant designed for the purpose, such as Caig
    De-Oxit, usually in a small aerosol can with a plastic extender tube. With
    the valve on the can set to LOW, one sprays a bit of cleaner into the
    control, aimed at the carbon element, if it's a potentiometer, or at the
    moving and stationary contacts, if it's a switch. Work the control back and
    forth numerous times. Usually we repeat the process.

    There's other fine points - such as blowing out the dust etc first, and
    packing tissue around the control to catch runoff and prevent a mess. Often
    it's necessary to hold the unit at some impossible angle so gravity can help
    get the cleaner where it needs to be. I will often blow out the controls
    again with a compressor and repeat the treatment, it's my belief that by so
    doing I blow out some of the debris loosened by the cleaning process.

    Mark Z.
  4. davesheb

    davesheb Guest

    Yes, the other inputs still work. Only the FM module kicks out. I would
    appreciate help with this. You've been helpful so far.
  5. davesheb

    davesheb Guest

    Is it difficult to find the bad transistor? I am send for the service
    manual and will probably give it to an experience repair place. Do you
    think this would be costly. Is this receiver worth the cost effort. Your
    opinion is appreciated. Thanks.
  6. The transistor to which I referred would cut out sound from all sources,
    since it is the pass transistor for the relay power supply voltage.

    It is a 2SC1438, if memory serves, located near the middle of the regulated
    power supply board on the underneath side of the unit.

    I can take no responsibility for the use or misuse of this information, and
    I hope that only a person of reasonable competence with electronic circuits
    will attempt this repair.

    Mark Z.
  7. Chuck

    Chuck Guest

    The board no. for this transistor was either Q9 or Q11. For fm
    cutting out on this unit, the blue Sanyo electrolytic capacitors on
    the tuner board would cause all kinds of intermittent problems. If
    you don't have an esr meter, we used to spot them by heating and
    cooling each in turn until the culprit showed up. Chuck.
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