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    THOMSON 32lb120s4 no sound

    Hi can anyone help please with cct diagram ,ive looked for hours
    this tv has no sound but the o/p stage is fine ,so suspect main board ,poss corrupt f/w?
    Attached Files

    #2
    Re: THOMSON 32lb120s4 no sound

    The THOMSON Chassis LCD12B 20LB120S4 may give you some insight into the audio section
    https://www.electronica-pt.com/esque...ileinfo/11059/
    Willing to help but I'm no expert.

    Comment


      #3
      Re: THOMSON 32lb120s4 no sound

      thanks for taking time to help .sadly this version you posted is different to mine the version i have has a TDA7490L for its sound o/p stage ,pin 6 of which is mute/on off .
      now when you press mute the osg shows on screen.
      the transistor q1 is used to switch mute on off
      there are 2 supplies -16v and +16v both present

      Comment


        #4
        Re: THOMSON 32lb120s4 no sound

        The osg displays? OSD? Are you you using remote or tv buttons? Do you get any mute message on screen?
        I assume no responsibility for any stupid suggestions I might post.

        Comment


          #5
          Re: THOMSON 32lb120s4 no sound

          yes mute osg as normal
          vol graphic as normal but not a peep of sound ,
          headphone socket also eliminated ,
          no sound with headphones

          Comment


            #6
            Re: THOMSON 32lb120s4 no sound

            Service menu : menu+info+103

            Comment


              #7
              Re: THOMSON 32lb120s4 no sound

              had a good look in s/menu
              sadly nothing in there to do with sound

              Comment


                #8
                Re: THOMSON 32lb120s4 no sound

                How did you verify the chip is good?
                I assume no responsibility for any stupid suggestions I might post.

                Comment


                  #9
                  Re: THOMSON 32lb120s4 no sound

                  supplies to chip ok slight buzz left and right on both i/p pins

                  Comment


                    #10
                    Re: THOMSON 32lb120s4 no sound

                    So you need 4-5vdc on pin 6 to make active. 0 to 2.5vdc to mute and standby.
                    I assume no responsibility for any stupid suggestions I might post.

                    Comment


                      #11
                      Re: THOMSON 32lb120s4 no sound

                      finally found cct .page 17 is audio o/p ,
                      strange theres no 5v supply shown on cct
                      it seems that the chip works without ?
                      please have a look
                      the cct is same even though the model number is 125 not 120
                      Attached Files

                      Comment


                        #12
                        Re: THOMSON 32lb120s4 no sound

                        So what voltage do you have on pin6?
                        I assume no responsibility for any stupid suggestions I might post.

                        Comment


                          #13
                          Re: THOMSON 32lb120s4 no sound

                          Originally posted by jimbofz View Post
                          finally found cct .page 17 is audio o/p ,
                          strange theres no 5v supply shown on cct
                          it seems that the chip works without ?
                          please have a look
                          the cct is same even though the model number is 125 not 120
                          The +5V and -5V are internally generated by the TDA7490L and available on pin 12 (+5V) and pin 16 (-5V).
                          The +5V (+VA5) then goes off to supply Q1 which controls the ON/OFF and Mute function.



                          https://cdn.badcaps-static.com/pdfs/...08f432f49f.pdf
                          Last edited by dick_barton; 11-20-2021, 05:23 PM.
                          Willing to help but I'm no expert.

                          Comment


                            #14
                            Re: THOMSON 32lb120s4 no sound

                            so that explaines where the 5v comes from .
                            its not clear from the cct .
                            i now understand its from within the ic

                            Comment


                              #15
                              Re: THOMSON 32lb120s4 no sound

                              Originally posted by dskall View Post
                              So you need 4-5vdc on pin 6 to make active. 0 to 2.5vdc to mute and standby.
                              the voltage is .05v ,so ill try to get replacement ic thanks

                              Comment


                                #16
                                Re: THOMSON 32lb120s4 no sound

                                You may have a faulty Q1 or the +5V from the TDA7490L may be missing or either the ON/OFF or MUTE signal may be stuck at +5V.
                                Last edited by dick_barton; 11-21-2021, 05:55 AM.
                                Willing to help but I'm no expert.

                                Comment


                                  #17
                                  Re: THOMSON 32lb120s4 no sound

                                  i will check as soon as i get my hands on the tv .the owner has taken it back and for the time being is using external audio out phonos from his sat box to his stereo system ,as he only uses scart on his tv ,uses the sound vol control on sat box. i will post update asap

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