Subwoofer Klipsch RW-12 No audio

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  • falcontech
    Badcaps Veteran
    • Oct 2013
    • 470
    • italy

    #1

    Subwoofer Klipsch RW-12 No audio

    good morning
    Today I find myself repairing this sub of which I have no audio output, the speaker is working, the amplification part is composed of three boards (as in the photo), power supply board, linear board and feature board, the sub turns on but I have no audio output, I have also attached the service manual, at the moment the only thing I noticed is that LM7815CT and LM7915CT heat up a lot and I don't know if it's normal, the capacitors at first glance all seem ok, I'm waiting someone tell me where to start testing (I state that I do not have an oscilloscope) thanks
    Attached Files
  • falcontech
    Badcaps Veteran
    • Oct 2013
    • 470
    • italy

    #2
    Re: Subwoofer Klipsh Rw-12 No audio

    all tensions are ok, +/- 25 +/- 15

    Comment

    • CapLeaker
      Leaking Member
      • Dec 2014
      • 8136
      • Canada

      #3
      Re: Subwoofer Klipsch RW-12 No audio

      The subwoofer should turn itself on when a signal is present on the input. Without a oscilloscope and audio generator makes it hard to trace the audio along the circuits and inject audio at certain points. This thing has a lot going on inside. You have to figure out if something at the input stage is blown, the feature stage or the output stage.

      Comment

      • falcontech
        Badcaps Veteran
        • Oct 2013
        • 470
        • italy

        #4
        Re: Subwoofer Klipsch RW-12 No audio

        Originally posted by CapLeaker
        The subwoofer should turn itself on when a signal is present on the input. Without a oscilloscope and audio generator makes it hard to trace the audio along the circuits and inject audio at certain points. This thing has a lot going on inside. You have to figure out if something at the input stage is blown, the feature stage or the output stage.
        not having an oscilloscope I try to do this with an amplified speaker and two test leads, I suppose the main suspects are the operational amplifiers or am I wrong?

        Comment

        • falcontech
          Badcaps Veteran
          • Oct 2013
          • 470
          • italy

          #5
          Re: Subwoofer Klipsch RW-12 No audio

          yesterday I had already started to do this test, the input audio stopped on an operational amplifier (the one highlighted in the photo), after I had nothing left, later I will deepen the thing
          Attached Files

          Comment

          • falcontech
            Badcaps Veteran
            • Oct 2013
            • 470
            • italy

            #6
            Re: Subwoofer Klipsch RW-12 No audio

            I did some tests, on the photos I posted there is a bit of a summary of what I perceived with the amplified speaker. the only signal I have is on the first op amp (very distorted) then it ends up on pin number 4 of the connector with a very dark and low sound. the same signal reaches the speaker connector but I repeat it is a very low and dark sound
            Attached Files

            Comment

            • CapLeaker
              Leaking Member
              • Dec 2014
              • 8136
              • Canada

              #7
              Re: Subwoofer Klipsch RW-12 No audio

              Originally posted by falcontech
              not having an oscilloscope I try to do this with an amplified speaker and two test leads, I suppose the main suspects are the operational amplifiers or am I wrong?
              Problem with that is you are going to load that circuit down. So that's not that good. Check the voltages with your DMM on the output of the op amps.

              Years ago I fixed a stereo encoder for a radio station. Worked fine until it got warm, then one channel would stop working. So I traced the audio from the input down the individual stages with an oscilloscope. Sure thing, didn't take me long to find an op-amp with signal in, but the output was dead and with -15VDC on it. Replaced both op amps (for each channel one at the same stage) and this thing is still working.

              Look at the block diagram in the schematic. This is a subwoofer. So it is only interested on the signals on the low end. The high end signals are going to get cut. That does make sense. Look at the block diagram and the manual. look at everything you can bypass, so the audio gets the least processing and straight to the amp in order to rule out other failure points. Look at U100 that should set you straight which direction you should go as part of it is the pre amp.
              Last edited by CapLeaker; 03-12-2022, 11:04 AM.

              Comment

              • falcontech
                Badcaps Veteran
                • Oct 2013
                • 470
                • italy

                #8
                Re: Subwoofer Klipsch RW-12 No audio

                Originally posted by CapLeaker
                Problem with that is you are going to load that circuit down. So that's not that good. Check the voltages with your DMM on the output of the op amps.

                Years ago I fixed a stereo encoder for a radio station. Worked fine until it got warm, then one channel would stop working. So I traced the audio from the input down the individual stages with an oscilloscope. Sure thing, didn't take me long to find an op-amp with signal in, but the output was dead and with -15VDC on it. Replaced both op amps (for each channel one at the same stage) and this thing is still working.

                Look at the block diagram in the schematic. This is a subwoofer. So it is only interested on the signals on the low end. The high end signals are going to get cut. That does make sense. Look at the block diagram and the manual. look at everything you can bypass, so the audio gets the least processing and straight to the amp in order to rule out other failure points. Look at U100 that should set you straight which direction you should go as part of it is the pre amp.
                All right I will try to do these tests and I will keep you updated

                Comment

                • falcontech
                  Badcaps Veteran
                  • Oct 2013
                  • 470
                  • italy

                  #9
                  Re: Subwoofer Klipsch RW-12 No audio

                  Originally posted by CapLeaker
                  Problem with that is you are going to load that circuit down. So that's not that good. Check the voltages with your DMM on the output of the op amps.

                  Years ago I fixed a stereo encoder for a radio station. Worked fine until it got warm, then one channel would stop working. So I traced the audio from the input down the individual stages with an oscilloscope. Sure thing, didn't take me long to find an op-amp with signal in, but the output was dead and with -15VDC on it. Replaced both op amps (for each channel one at the same stage) and this thing is still working.

                  Look at the block diagram in the schematic. This is a subwoofer. So it is only interested on the signals on the low end. The high end signals are going to get cut. That does make sense. Look at the block diagram and the manual. look at everything you can bypass, so the audio gets the least processing and straight to the amp in order to rule out other failure points. Look at U100 that should set you straight which direction you should go as part of it is the pre amp.
                  in the photo I reported, the outputs that could have anomalies, the other opamps do not report anything at the output
                  Attached Files

                  Comment

                  • CapLeaker
                    Leaking Member
                    • Dec 2014
                    • 8136
                    • Canada

                    #10
                    Re: Subwoofer Klipsch RW-12 No audio

                    check U100

                    Comment

                    • falcontech
                      Badcaps Veteran
                      • Oct 2013
                      • 470
                      • italy

                      #11
                      Re: Subwoofer Klipsch RW-12 No audio

                      Originally posted by CapLeaker
                      check U100
                      I checked all the outputs are at 0

                      Comment

                      • falcontech
                        Badcaps Veteran
                        • Oct 2013
                        • 470
                        • italy

                        #12
                        Re: Subwoofer Klipsch RW-12 No audio

                        Originally posted by CapLeaker
                        check U100
                        what do i replace suspicious opamps?

                        Comment

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