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Samsung LN40B5ooP3FXZA Cycling on/Off

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    Samsung LN40B5ooP3FXZA Cycling on/Off

    Have a Samsung given to me. When power is applied backlights will come on and stay on for approximately 10 seconds then power off and then on once again. When looking at the back lights from the rear they appear to be flickering. Tried disconnecting the cable from the power supply to the main board when it powers up and there appears to be no flicker however display will only remain on for 3 seconds with the cable disconnected.. Tried disconnecting the TCONN board with no change. I suspect the main board BN94-02746Y.
    I am unable to purchase a repair kit for this board and replacement boards are out of the question. Has anyone had experience with this type of failure and is there a common failure point on this board that I could investigate.

    Thank you to everyone for your time to look at this post.

    #2
    Re: Samsung LN40B5ooP3FXZA Cycling on/Off

    Usually if the backlights do not stay on with cable from powerboard to mainboard unhooked, you have a backlight or powerboard issue that must be corrected first.
    Last edited by nomoresonys; 01-15-2021, 02:34 PM.

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      #3
      Re: Samsung LN40B5ooP3FXZA Cycling on/Off

      i've had two LN40B530 that would power on the CCFL, but after 3 seconds they would shut down and blink the red standby LED, disconnecting the main board from the power supoply should light all the lamps and not shut down.

      Solution: replaced some defective CCFL lamps. If it cycles the lamps on and off I don't know what could it be, possibly the PSU, but this series has notorious problems with lamps heating too much and failing.

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        #4
        Re: Samsung LN40B5ooP3FXZA Cycling on/Off

        Might be worth checking the PFC volts on power supply .

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          #5
          Re: Samsung LN40B5ooP3FXZA Cycling on/Off

          Thank you everyone for your input. I was leaning towards a bad main board. Just to be clear if I disconnect the connector to the main board the backlights should remain on? As previously stated I get about 10 seconds when connected but only about three seconds if I disconnect the cable to the main board as soon as the backlights are on. This is why I suspected the main board possibly not sending a return signal to the power board to remain on. Just my thoughts.

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            #6
            Re: Samsung LN40B5ooP3FXZA Cycling on/Off

            NOPE, reread post #2, meaning there's a problem with the backlights or powerboard, you might not even have a problem with the mainboard but there is for sure a problem before it as stated.
            Last edited by nomoresonys; 01-16-2021, 07:23 AM.

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              #7
              Re: Samsung LN40B5ooP3FXZA Cycling on/Off

              I would also check the resistance of the inverter transformers and ensure they match each other.

              Is there any discolouration on the underside of the circuit board below any of the transformers.

              Are all the transformer solder joints sound.
              Willing to help but I'm no expert.

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                #8
                Re: Samsung LN40B5ooP3FXZA Cycling on/Off

                Show us good clear pictures of the whole backside of the TV showing all the boards and then straight shots pictures of each board will help.
                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

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                  #9
                  Re: Samsung LN40B5ooP3FXZA Cycling on/Off

                  Wow thank you so much for all your help. I believe I found the problem. Hopefully optimistic. I found that on assembly of the TV a screw that holds the back cover on the TV in the center went through the cable between the power supply module and the main board. I split the ribbon cable and repaired the wires and the TV has worked for a few hours now. If I get an opportunity I will take the recommended pictures for everyones reference perhaps on another TV or possibly this one if it fails again.
                  Last edited by BruceGilbert; 01-17-2021, 06:03 AM.

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                    #10
                    Re: Samsung LN40B5ooP3FXZA Cycling on/Off

                    Ok, strange tho that the backlight didn't stay on when cable from powerboard to mainboard was unplugged, pretty sure a recent LN40 I dealt with did stay on but maybe it wasn't a LN40B.
                    Last edited by nomoresonys; 01-17-2021, 10:27 AM.

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