Marantz 1030: Extreme Bias Voltage and Distortion on Left Channel

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  • TechGeek
    Computer Geek
    • Jan 2015
    • 2254
    • USA
    #1

    Marantz 1030: Extreme Bias Voltage and Distortion on Left Channel

    Hey all. I have this Marantz model 1030 amplifier with some problems.

    Problem 1: Left channel has extreme distortion under any kind of load. If you crank the bass control, it distorts to hell and gone.

    Problem 2: When attempting to set the bias voltage for the left channel, it's ENTIRELY too high. The service manual states 7.5mVDC at idle. It won't go below 130mV. The right channel has no distortion and I was able to successfully set it's bias current to 7.5mV.

    I think what's going on here is that something is pulling the bias voltage way up on the left channel and when you load that channel down, the high bias voltage causes the transistor to be driven into distortion.

    What might be pulling the bias voltage up? Will this kill the transistors in short order?

    TIA.

    Service Manual: https://cdn.badcaps-static.com/pdfs/...739e9f0da8.pdf
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    • andy1
      New Member
      • Apr 2019
      • 9
      • USA
      #2
      Re: Marantz 1030: Extreme Bias Voltage and Distortion on Left Channel

      I would disconnect the speakers (to be safe) and turn down the volume control and start comparing voltages with the working channel. There are just a handful of components to check and it should be quite easy to do that. Pay attention to the transistors H 501-506 and the nearby parts. Also, if you can lift those transistors and check them individually, you should be able to narrow down easily.

        Comment

        • petehall347
          Badcaps Legend
          • Jan 2015
          • 4426
          • United Kingdom
          #3
          Re: Marantz 1030: Extreme Bias Voltage and Distortion on Left Channel

          test emitter resistors values ...
          are the outputs running very hot ?

            Comment

            • redwire
              Badcaps Legend
              • Dec 2010
              • 3906
              • Canada
              #4
              Re: Marantz 1030: Extreme Bias Voltage and Distortion on Left Channel

              I think it's a quasi-complementary output stage, so the bias works differently.

              To check the transistors I would compare readings between channels (power off, with multimeter on diode test) of the output transistor and driver VBE junctions. Also the bias diode array, if they are high Vf then bias would be high. I think SV-03A brown boat can be replaced by three Vishay 1N4150's in series, for 2.18V at 1mA. More info on them here:
              https://audiokarma.org/forums/index....acement.756284

              Rarely, high bias and distortion is from oscillations, if the electrolytics are low value.

                Comment

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