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Insignia NS-39L700A12 backlight transformer high pitched wine

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    #21
    Re: Insignia NS-39L700A12 backlight transformer high pitched wine

    Originally posted by R_J View Post
    I asked for the emitter & collector voltages to see if the ic's had the proper vcc, Since you did'nt post it here, I suggest you look up the ic's datasheet and see if they are correct.
    I meant to post pics, here they are.
    Attached Files

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      #22
      Re: Insignia NS-39L700A12 backlight transformer high pitched wine

      If the 18v is stable then it should be ok, if it is slow to build up to 18v then there is a problem. To be sure of the voltage I would need the part numbers on N504 & N501

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        #23
        Re: Insignia NS-39L700A12 backlight transformer high pitched wine

        Originally posted by R_J View Post
        If the 18v is stable then it should be ok, if it is slow to build up to 18v then there is a problem. To be sure of the voltage I would need the part numbers on N504 & N501
        Here are pictures of N504 and N501. I forgot to mention the Emitter voltage at standby is 21.5v
        Attached Files
        Last edited by MikeRWK; 01-25-2021, 12:11 AM.

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          #24
          Re: Insignia NS-39L700A12 backlight transformer high pitched wine

          Should the voltage on the emitter fluctuate like this with the tv off? https://streamable.com/x4o0z1

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            #25
            Re: Insignia NS-39L700A12 backlight transformer high pitched wine

            18 volts is fine for the main & pfc ic's The emitter voltage will be higher in standby because the transistor is turned off. So is the vcc voltage in standby 21.5v or is iI changing? In standby, N503 is in burst mode so the vcc voltage could be changing, or the capacitor for that voltage is bad. The standby ic also uses this voltage but only requires it to be around 15 volts (stop voltage is 8.1v) in standby
            Last edited by R_J; 01-25-2021, 12:55 PM.

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              #26
              Re: Insignia NS-39L700A12 backlight transformer high pitched wine

              I replaced all the electrolytic caps with known good ones and it's still got the high pitched noise coming from the transformer. What causes transformer whine?

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                #27
                Re: Insignia NS-39L700A12 backlight transformer high pitched wine

                L601 is NOT a transformer, it is just a coil (inductor) In this case it is used to boost the led voltage, Is the base supply voltage ok and clean? If the supply is not filtered properly, there can be a beat frequency between the main supply transformer frequency and the led driver frequency.
                Or it could just be due to loose windings or cracked core in the coil. Are the backlights ok and does the whine change with if you change the backlight level?
                Last edited by R_J; 01-25-2021, 04:14 PM.

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                  #28
                  Re: Insignia NS-39L700A12 backlight transformer high pitched wine

                  Originally posted by R_J View Post
                  L601 is NOT a transformer, it is just a coil (inductor) In this case it is used to boost the led voltage, Is the base supply voltage ok and clean? If the supply is not filtered properly, there can be a beat frequency between the main supply transformer frequency and the led driver frequency.
                  Or it could just be due to loose windings or cracked core in the coil. Are the backlights ok and does the whine change with if you change the backlight level?
                  The backlights flicker, the inductor noise changes when I push on it

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                    #29
                    Re: Insignia NS-39L700A12 backlight transformer high pitched wine

                    I've decided to scrap the tv it was free anyways.

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                      #30
                      Re: Insignia NS-39L700A12 backlight transformer high pitched wine

                      Originally posted by MikeRWK View Post
                      The backlights flicker, the inductor noise changes when I push on it
                      There could be a fault with the led's causing the problem, carefully remove the lcd panel & diffusers and see if there are some bad led's.

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