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    Kenwood KR-A4070 Sound issue

    The sound is very low. You can crank the volume up fully and not a lot of sound. I am not very familiar with audio circuits. Can someone look at the schematic and tell me where to look. I do have a 70MHz oscilloscope. Any help would be greatly appreciated?

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    #2
    Re: Kenwood KR-A4070 Sound issue

    Did try cleaning the controls and switches first?
    This unit uses lots of electronic switch ICs (IC 102, 104) for routing the audio signals which do go bad.
    Since you are getting low sound form both channels I would then look at the circuits that are common to both channel by checking to make sure the power supply Voltages are OK, also make sure all the boards mounting screws are tight and not corroded which will cause bad Ground connection to the chassis.
    You can also look at the audio signals on CN101 RIN, ROUT, LIN, LOUT.
    The schematic is kind of bad due to multiple pages you need to link them together.
    Last edited by budm; 12-02-2015, 08:09 PM.
    Never stop learning
    Basic LCD TV and Monitor troubleshooting guides.
    http://www.badcaps.net/forum/showthr...956#post305956

    Voltage Regulator (LDO) testing:
    http://www.badcaps.net/forum/showthr...999#post300999

    Inverter testing using old CFL:
    http://www.badcaps.net/forum/showthr...er+testing+cfl

    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
    http://s807.photobucket.com/user/budm/library/

    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

    Comment


      #3
      Re: Kenwood KR-A4070 Sound issue

      thanks budm. I did find that one of the connectors says -30V, but when I measured it I only got -25v. I agree the schematics suck.

      Comment


        #4
        Re: Kenwood KR-A4070 Sound issue

        I think the -30V is used for the FL (Fluorescent Display), I need to look at the SCH.
        Never stop learning
        Basic LCD TV and Monitor troubleshooting guides.
        http://www.badcaps.net/forum/showthr...956#post305956

        Voltage Regulator (LDO) testing:
        http://www.badcaps.net/forum/showthr...999#post300999

        Inverter testing using old CFL:
        http://www.badcaps.net/forum/showthr...er+testing+cfl

        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
        http://s807.photobucket.com/user/budm/library/

        TV Factory reset codes listing:
        http://www.badcaps.net/forum/showthread.php?t=24809

        Comment


          #5
          Re: Kenwood KR-A4070 Sound issue

          I input audio to the CD input port and I do get Left and Right audio going into IC104 and out of IC102.
          I get nothing at CN101. What does IC106 do? Its says UP/DOWN.
          Last edited by tech2014; 12-03-2015, 05:30 PM.

          Comment


            #6
            Re: Kenwood KR-A4070 Sound issue

            Originally posted by tech2014 View Post
            I input audio to the CD input port and I do get Left and Right audio going into IC104 and out of IC102.
            I get nothing at CN101. What does IC106 do? Its says UP/DOWN.
            Volume Control motor drive.
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #7
              Re: Kenwood KR-A4070 Sound issue

              thanks. I am suspecting IC104 since I get nothing at CN101.

              Comment


                #8
                Re: Kenwood KR-A4070 Sound issue

                If you look at PDF page 18, CN101 PIN 3 is the LEFT channel power amp input, pin 6 is the Right channel power amp input.
                Q101, Q102 are the MUTE transistors for the power amp inputs which should be turned off in normal operation (not in MUTE mode).
                So what audio signal do you see at the CN101?
                Last edited by budm; 12-03-2015, 05:55 PM.
                Never stop learning
                Basic LCD TV and Monitor troubleshooting guides.
                http://www.badcaps.net/forum/showthr...956#post305956

                Voltage Regulator (LDO) testing:
                http://www.badcaps.net/forum/showthr...999#post300999

                Inverter testing using old CFL:
                http://www.badcaps.net/forum/showthr...er+testing+cfl

                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                http://s807.photobucket.com/user/budm/library/

                TV Factory reset codes listing:
                http://www.badcaps.net/forum/showthread.php?t=24809

                Comment


                  #9
                  Re: Kenwood KR-A4070 Sound issue

                  I can't see anything at all.

                  Comment


                    #10
                    Re: Kenwood KR-A4070 Sound issue

                    So you do see audio on pin 21 INPUT (L) of IC104 but no output on pin 19 (L)?
                    BTW, the diagram shows IC104 PIN19, 20, 21 are tied together directly!, SAME FOR 8, 9, and 10 for the Right channel. Is that how they are connected?
                    Last edited by budm; 12-03-2015, 06:09 PM.
                    Never stop learning
                    Basic LCD TV and Monitor troubleshooting guides.
                    http://www.badcaps.net/forum/showthr...956#post305956

                    Voltage Regulator (LDO) testing:
                    http://www.badcaps.net/forum/showthr...999#post300999

                    Inverter testing using old CFL:
                    http://www.badcaps.net/forum/showthr...er+testing+cfl

                    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                    http://s807.photobucket.com/user/budm/library/

                    TV Factory reset codes listing:
                    http://www.badcaps.net/forum/showthread.php?t=24809

                    Comment


                      #11
                      Re: Kenwood KR-A4070 Sound issue

                      I did see -1.6V on the base of Q101 and Q102. Are they supposed to be 0 when in mute or is this normal. Im done for the day. I will get back to it tomorrow and get back to you on my findings. Thanks for the help, learning lots today.
                      Last edited by tech2014; 12-03-2015, 06:10 PM.

                      Comment


                        #12
                        Re: Kenwood KR-A4070 Sound issue

                        Found something strange. I think the input selector IC may be shot. When testing the other inputs, like the CD/TAPE/PHONO, I had the audio connected to the TAPE 1/REC input, and I was getting normal sound. Problem is I can change the input to TUNER or CD, and still get sound. Should only be sound coming out of the input selected. Since there was no audio connected to the CD or PHONO inputs, but I get normal sounding audio coming out, would this point to the input selector. I even get sound out of the TUNER even though there is no antenna connected.

                        I also noticed that if I get low sound on the CD input when there is audio signal, if I toggle between inputs, and select CD, I can get the sound back to normal again.
                        Last edited by tech2014; 12-04-2015, 02:29 PM.

                        Comment


                          #13
                          Re: Kenwood KR-A4070 Sound issue

                          I'm confused. I input the sine wave and trace it to CN101. I get L and R IN but no L and R OUT. I get normal volume out of the speakers
                          Last edited by tech2014; 12-04-2015, 03:15 PM.

                          Comment


                            #14
                            Re: Kenwood KR-A4070 Sound issue

                            'Problem is I can change the input to TUNER or CD, and still get sound. Should only be sound coming out of the input selected. ' That is correct, I wonder if it is stuck in one of the input mode, you may have to try feeding each input to see which one will give the normal sound level.
                            You also verify that the TAPE MONITOR is not activated, right?
                            Never stop learning
                            Basic LCD TV and Monitor troubleshooting guides.
                            http://www.badcaps.net/forum/showthr...956#post305956

                            Voltage Regulator (LDO) testing:
                            http://www.badcaps.net/forum/showthr...999#post300999

                            Inverter testing using old CFL:
                            http://www.badcaps.net/forum/showthr...er+testing+cfl

                            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                            http://s807.photobucket.com/user/budm/library/

                            TV Factory reset codes listing:
                            http://www.badcaps.net/forum/showthread.php?t=24809

                            Comment


                              #15
                              Re: Kenwood KR-A4070 Sound issue

                              I have CD input selected using the sine wave as a signal. For some reason, no matter what input I select, I have a signal on pin 3 and pin 26 of both IC102 and IC104.

                              I connected the signal to TAPE 2 MONITOR, I get signal out of REC but not PLAY. Same on TAPE 1

                              Comment


                                #16
                                Re: Kenwood KR-A4070 Sound issue

                                So could it be IC102 and IC104?

                                Comment


                                  #17
                                  Re: Kenwood KR-A4070 Sound issue

                                  Pin 3 and 26 of IC102 are always on no matter what input is selected.

                                  Comment


                                    #18
                                    Re: Kenwood KR-A4070 Sound issue

                                    I found bad solder on IC, resoldered and works now.

                                    Comment

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