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After 10 years of function a problem appears with the technics se-a900s power amplifier: When the power output reaches or aprox the 10wrms the protection circuit enabled,and the unit goes off! (no sound) I have to turned off power,and start again (power on) The unit is not overheating. The built in cooling fan working fine. I dont want to think that the problem caused from the 15y.old,speakers,they playing music fine as the first time! (tested with other type of amplifiers at high levels of power with the same cables) I think something going wrong with the thermal detector or low impedance speaker detector - i couldn't found any adjastments for this inside the unit!

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  • qluser Oct 12, 2010

    After a close look at the schematic diagram of the amplifier, i saw there is no thermal protection circuits with discrette componets.
    However the problem i think caused from bad voltage,combined with poor current from power supply unit. Special from the capacitors. They are aged...
    I will try to replace them,and i will post a comment,with test results.

    Somehow ,if i run the amplifier from the first at high level output, the unit working fine!
    If i run the amplifier at low power output for several hours,and then want to hear at high level,the problem appear especially at night! (diefrent and higher ac voltage)
    Also important is this: I don't hear music verry often from this system. The amplifier is in function for 2-3 months,and sometimes more for the last 5 years! Before this period the amplifier working fine day by day for a several hours per day.


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I would have the power supply capacitors replaced. After several years ( from heat and age) they dry out and dont put out proper DC voltages to run the amp.

Posted on Oct 12, 2010

  • 2 more comments 
  • qluser Oct 12, 2010

    I thought that too... Thanks any way!

  • fastbladerun Jan 18, 2011

    Can you let me know if that was the solution please?
    I have the same problem en where did you buy these capacitors.
    Thanks Paul

  • fastbladerun Apr 05, 2011

    Please can you tel me if the capacitors where the problem or something else

  • Scott Frye
    Scott Frye Apr 05, 2011

    Digikey (dot) com or
    mouser (dot) com


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