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No power on Samsung LN40B500P3FXZA, but Caps look ok?

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    #1

    No power on Samsung LN40B500P3FXZA, but Caps look ok?

    Hello everyone! I have a Samsung LN40B500P3FXZA that will not power on. No Power LED, and no leaky Caps. I disconnected the Mainboard and the back light did not power on. I suppose the next step would be to check the Mosfets and Bridge Rectifier? I'm just not sure exactly how to go about that?

    There was also a residue on the Mainboard where the cushion was. Not sure if that was normal. Any help you guys can provide is greatly appreciated!











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    #2
    Re: No power on Samsung LN40B500P3FXZA, but Caps look ok?

    Check the fuse next to the two large caps. on the power supply board, also check the two fets on the other side of those two caps. I just had one of those boards and there were bad connections on the fets and also another ic mounted to one of the heatsinks.
    the fets were shorted and blew the fuse.

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      #3
      Re: No power on Samsung LN40B500P3FXZA, but Caps look ok?

      Thanks for the fast reply!!

      How do I check the Fets? Just for a good connection? Or is there something I need to do with a MM?

      Also, how can I tell if the fuse is bad? These are Ceramic correct?

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        #4
        Re: No power on Samsung LN40B500P3FXZA, but Caps look ok?

        Do you have a digital multimeter?
        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

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          #5
          Re: No power on Samsung LN40B500P3FXZA, but Caps look ok?

          Originally posted by tom66 View Post
          Do you have a digital multimeter?

          Sorry, jumped the gun with the questions. I do, and just looked up how to test ceramic fuses. Same go for the Fets? Just test for continuity?

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            #6
            Re: No power on Samsung LN40B500P3FXZA, but Caps look ok?

            I have the same unit Samsung LN40B500P3FXZA no power led, however the back lights do come on. I removed the back and have performed all the test tips so far on this model from this site. Great stuff appreciate it.

            Ok I've tested V at 29/30 connection and randomly across the pwr board, they are a little low, the 13V are 12.59 to 12.94v, and the 5.3v is 4.96 to 5.29v. tested the 2 fuses and the fets by the big caps no continuity. no caps popped.
            Plug in the a/c and the back-lights come on.
            Went to the main board and pulled it, the same flux issue previously noted by thread starter.

            I'm to assume since the pwr-brd does provide the specified output voltages it's the main board?

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              #7
              Re: No power on Samsung LN40B500P3FXZA, but Caps look ok?

              I HAVE A LN40B500P3FXZA,POWER COMES ON WITH BACKLIGHT AND THEN GOES OUT,

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