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TCL 75R615 has sound, no backlight

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    #21
    Re: TCL 75R615 has sound, no backlight

    Need the part numbers to know the gate, source and drain. Many videos on how to test.
    I assume no responsibility for any stupid suggestions I might post.

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      #22
      Re: TCL 75R615 has sound, no backlight

      Originally posted by thetonywarren View Post
      Ok, does anyone have a good source for how I should be testing these particular mosfets? Ive viewed a few videos on youtube, but just looking for suggestions.....

      Thanks!
      If they don't check shorted, they are very likely ok. For a proper test you need to remove them and that could just cause more problems.

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        #23
        Re: TCL 75R615 has sound, no backlight

        Ok, so I removed the heatsink that attaches to the two mosfets, I understand this is probably overkill but I wanted to be as throrough as possible. Please see the attached picture with both of the mosfets, I believe thy are MDF18N50, also see the attached link with the data sheet for reference....

        https://datasheetspdf.com/pdf/830304...hip/MDF18N50/1

        I will attempt to test both of these components per this video......

        https://youtu.be/gloikp9t2dA
        Attached Files

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          #24
          Re: TCL 75R615 has sound, no backlight

          I am still struggling in testing out these two mosfets, Im unable to re-create the testing results using 3 different multimeters I have with diode mode......Im not sure if Im doing something wrong or if there's something specific about these components that would prevent me from using a standard inexpensive multimeter in diode mode to test......any help is much appreciated......

          Thanks in advance!!!

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            #25
            Re: TCL 75R615 has sound, no backlight

            Originally posted by thetonywarren View Post
            I am still struggling in testing out these two mosfets, Im unable to re-create the testing results using 3 different multimeters I have with diode mode......Im not sure if Im doing something wrong or if there's something specific about these components that would prevent me from using a standard inexpensive multimeter in diode mode to test......any help is much appreciated......

            Thanks in advance!!!
            I have one of these testers as i do find testing certain parts at times hard
            https://www.ebay.co.uk/itm/143173138...YAAOSwPF9ci9rw

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              #26
              Re: TCL 75R615 has sound, no backlight

              I maybe wrong here but I think your problem is that your gate to source is 10v to turn on mosfet. Your meter may not be able to do that.
              Last edited by dskall; 12-08-2021, 10:42 AM.
              I assume no responsibility for any stupid suggestions I might post.

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                #27
                Re: TCL 75R615 has sound, no backlight

                I kind of thought about that, even though I was not sure.....is it because my meter is powered with a 9v battery it doesnt have enough voltage to trigger the mosfet to turn on/off? I know that description is pretty crude/simple, just trying to understand the concepts.....If that's the case Im guessing i'd need a more powerful DMM or a bench type meter that plugs into the wall? Regardless, Im purchasing one of those cheap LCR tester meters on amazon to try and sort things out.....

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                  #28
                  Re: TCL 75R615 has sound, no backlight

                  I replaced the cap as well as resoldering the heatsink and mosfets. I was too impatient to wait for the LCR meter to arrive. TV seems to power up normally!!! Great news. Thanks to all for the help and advice.
                  Attached Files

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                    #29
                    Re: TCL 75R615 has sound, no backlight

                    Thanks for feedback.
                    I assume no responsibility for any stupid suggestions I might post.

                    Comment


                      #30
                      Re: TCL 75R615 has sound, no backlight

                      thetonywarren do you happen to have any high resolution photos of the back of the power supply board? My TV recently stopped working and I was able to find some components that were blown related to the 24V main supply. I was able to replace QW401 and R404, but there is a small resistor on the back side (R402) that is part of the gate drive circuit that has a hole blown right through the part marking. Hoping I can find the resistor size in a high resolution image.

                      Any help you can provide would be appreciated, thanks in advance!

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                        #31
                        Re: TCL 75R615 has sound, no backlight

                        The only pictures I have are the ones from post #3. Other than that, the TV has been working since the repair, use it every day pretty much.

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