Technics SA-5550, powers on but no sound.

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  • johnboy1313
    Badcaps Legend
    • Nov 2012
    • 1959
    • USA

    #1

    Technics SA-5550, powers on but no sound.

    I found this in a dumpster. I've fixed many TVs at this point but no audio equipment yet. It powers on. It plays a weak sound through at least one side of the headphones but it's not loud at all. I was using my iphone earbuds with a 1/4" mono adapter so I don't know for sure if one side doesn't work through the phones jack or if the adapter was causing it. I opened it up and noticed the burnt spot in the pictures. I don't know the insides of audio equipment like I know TVs so I really don't know where to go from here. Something failed violently. It looks like only one of the transistors (TR603) near the burned mark is shorted and a couple resistors are toast. Both of the speaker circuit protection fuses are missing. I probed the clips that hold the fuses for voltage and continuity to ground. When power is on, the left channel fuse show about 190mv. The right channel shows 14.45V. The other clip on the right channel is shorted to ground. Ive attached the service manual and a few pics. I can provide more when needed.
    Attached Files
    Last edited by johnboy1313; 05-18-2016, 08:49 PM.
  • johnboy1313
    Badcaps Legend
    • Nov 2012
    • 1959
    • USA

    #2
    Re: Technics SA-5550, powers on but no sound.

    I'm on my phone now so I can only post one pic at a time.
    Attached Files

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    • johnboy1313
      Badcaps Legend
      • Nov 2012
      • 1959
      • USA

      #3
      Re: Technics SA-5550, powers on but no sound.

      Picture
      Attached Files

      Comment

      • johnboy1313
        Badcaps Legend
        • Nov 2012
        • 1959
        • USA

        #4
        Re: Technics SA-5550, powers on but no sound.

        Another pic
        Attached Files

        Comment

        • johnboy1313
          Badcaps Legend
          • Nov 2012
          • 1959
          • USA

          #5
          Re: Technics SA-5550, powers on but no sound.

          Schematic for the burnt board.
          Attached Files

          Comment

          • johnboy1313
            Badcaps Legend
            • Nov 2012
            • 1959
            • USA

            #6
            Re: Technics SA-5550, powers on but no sound.

            TR604, TR606, TR607, and TR608 are all shorted as well.

            Comment

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