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    Strange malfunctioning LED audio peak level meter problem

    So, I just got this old Harmon Kardon TD292 cassette player. It plays, but there are two groups of three LED's, one on each channel of the peak level meter, that aren't lighting up. I've done some minor electronic repair, but I can' figure this one out. I've taken it apart, but I don't see anything out of the ordinary. I don't know what "drives" these groups of LED's. These LED's light up individually, but I'm assuming there's something "assigned" to drive them in "three's", yes? The housing the LED's are in is mounted to a small board in a way that you can't see the individual LED's nor their connections to the little board they're on. Any ideas where to start?
    Attached Files
    Last edited by JimBanville; 08-11-2020, 04:26 PM.

    #2
    Re: Strange malfunctioning LED audio peak level meter problem

    check the soldering around both ic chips

    Comment


      #3
      Re: Strange malfunctioning LED audio peak level meter problem

      Originally posted by petehall347 View Post
      check the soldering around both ic chips
      Thanks for the reply, but which IC chips? I mean, do you know where they're located? This is a pic of the main board. The only things on the meter's tiny board are couple caps and resistors. There's a small rectangular box that houses the LED's. Are the chips inside there? I don't see a way to open it up. There is nothing on the opposite side of the board, under the
      "box".
      Attached Files
      Last edited by JimBanville; 08-11-2020, 05:22 PM.

      Comment


        #4
        Re: Strange malfunctioning LED audio peak level meter problem

        the 2 biggest ones .

        Comment


          #5
          Re: Strange malfunctioning LED audio peak level meter problem

          Originally posted by petehall347 View Post
          the 2 biggest ones .
          Ok. The biggest ones are pair of DOLBY chips (one for each chanel I guess).

          From tha manual...
          Attached Files

          Comment


            #6
            Re: Strange malfunctioning LED audio peak level meter problem

            Show us good clear pictures of the inside of the unit and the boards.
            The LED meter assembly should have the LED driver IC's on that board, so check for bad the solder joints first.
            Can you upload the service manual?
            Never mind, I found the service manual.
            Attached Files
            Last edited by budm; 08-11-2020, 06:15 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


              #7
              Re: Strange malfunctioning LED audio peak level meter problem

              Originally posted by JimBanville View Post
              Thanks for the reply, but which IC chips? I mean, do you know where they're located? This is a pic of the main board. The only things on the meter's tiny board are couple caps and resistors. There's a small rectangular box that houses the LED's. Are the chips inside there? I don't see a way to open it up. There is nothing on the opposite side of the board, under the
              "box".
              Judging by the schematic you provided in your startpost, the 2 driver IC's are indeed located on the PCB holding the LED's. This PCB is connected to the mainboard through a 8 wire flatcable of some sorts. The connector is the one on the lower side of the mainboard shown on the photo in post 3, just below the text 'Meter Level Adj'.

              re-atari
              Last edited by re-atari; 08-11-2020, 05:49 PM.

              Comment


                #8
                Re: Strange malfunctioning LED audio peak level meter problem

                The VU meter LED driver IC has them in groups of three LED's.
                If one LED goes open, the set of three goes dead. Put your multimeter on diode-test and see if the LED's are ok. Or cold solder joints. What is the IC's part number?
                A similar one is the UAA180 but I'll bet your HK uses Hitachi parts. Or maybe the red LED's died, I have seen that too.

                Comment


                  #9
                  Re: Strange malfunctioning LED audio peak level meter problem

                  Originally posted by redwire View Post
                  The VU meter LED driver IC has them in groups of three LED's.
                  If one LED goes open, the set of three goes dead. Put your multimeter on diode-test and see if the LED's are ok. Or cold solder joints. What is the IC's part number?
                  A similar one is the UAA180 but I'll bet your HK uses Hitachi parts. Or maybe the red LED's died, I have seen that too.
                  Ok. If they're on the same board as the LED's I have to figure out how to open up the plastic box they're in.

                  Comment


                    #10
                    Re: Strange malfunctioning LED audio peak level meter problem

                    are they not through hole devices ?

                    Comment


                      #11
                      Re: Strange malfunctioning LED audio peak level meter problem

                      pics would be handy

                      Comment


                        #12
                        Re: Strange malfunctioning LED audio peak level meter problem

                        Originally posted by petehall347 View Post
                        pics would be handy
                        Pics of led board
                        Attached Files

                        Comment


                          #13
                          Re: Strange malfunctioning LED audio peak level meter problem

                          Yep, one of those encapsulated (Black blob) IC on PCB.
                          It looks like the LED's pins are mated to the PCB using pressure to make contact with the PCB pads.
                          If you flex the board you may see the LED come and go.
                          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


                            #14
                            Re: Strange malfunctioning LED audio peak level meter problem

                            Originally posted by budm View Post
                            Yep, one of those encapsulated (Black blob) IC on PCB.
                            It looks like the LED's pins are mated to the PCB using pressure to make contact with the PCB pads.
                            If you flex the board you may see the LED come and go.
                            So what do u think I should do next? IC problem? Dead LED's? Bad led connections?

                            Comment


                              #15
                              Re: Strange malfunctioning LED audio peak level meter problem

                              Did you try flexing the board while power up with signal so you can see flexing will cause the LED's to come and go?
                              https://www.badcaps.net/forum/attach...3&d=1597194394
                              Those white plastic dots look to holding the LED assembly to make contact with the PCB.
                              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


                                #16
                                Re: Strange malfunctioning LED audio peak level meter problem

                                What I have done when desperate to repair vintage gear is VERY CAREFULLY remove the LED diffuser assembly to access the naked LED's on the PC board. This means cutting/remelting or removing the six plastic pins and pulling off the LED diffuser straight up. If you slide it sideways it will kill all LED's by shearing off the bonding wires. I expect raw LED dies on the PC board with a tiny bonding wire.
                                You could also just carefully peel off the diffuser overlay to see what's inside.

                                I would solder in 0603 LED's to replace the defective ones.

                                edit: to get troubleshoot kind of displays to work in the shop we used freeze spray drops on an LED. I think they get a bad connection to the die, the bonding wire doesn't quite work.
                                Last edited by redwire; 08-11-2020, 10:23 PM.

                                Comment


                                  #17
                                  Re: Strange malfunctioning LED audio peak level meter problem

                                  https://www.badcaps.net/forum/attach...1&d=1597194394
                                  I wonder what you will see if you look straight from the side view.
                                  Last edited by budm; 08-11-2020, 11:07 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


                                    #18
                                    Re: Strange malfunctioning LED audio peak level meter problem

                                    Originally posted by budm View Post
                                    Did you try flexing the board while power up with signal so you can see flexing will cause the LED's to come and go?
                                    https://www.badcaps.net/forum/attach...3&d=1597194394
                                    Those white plastic dots look to holding the LED assembly to make contact with the PCB.

                                    I tried flexing it. No joy.

                                    Comment


                                      #19
                                      Re: Strange malfunctioning LED audio peak level meter problem

                                      Cover came off easily after I used a razor blade to slice the white plastic tabs off the back.
                                      Attached Files

                                      Comment


                                        #20
                                        Re: Strange malfunctioning LED audio peak level meter problem

                                        you can use the testpoints either with another led or a multimeter on diode-test

                                        Comment

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