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m471i-a2 no backlight

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    #1

    m471i-a2 no backlight

    I have no back light and was hoping I cold get some information on the transistors in the picture. As you can see one is for sure shot but i was going to replace them all while I was at it. I am unsure how to identify the components I need however. If I could get pointed in the right direction I would forever grateful.

    Thanks
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    #2
    Re: m471i-a2 no backlight

    there are 3 things you need to check. Does the main board send PSon and BLon signals? Does the PSU provide power to the backlights, or is it a LED that's bad on the backlight strip? So you would have to get a digital multimeter and start measuring things.

    Comment

      #3
      Re: m471i-a2 no backlight

      You have 6 strings of LEDs so that is why there are 6 PWM controlled MOSFET to maintain constant current through each LED string.
      I can see that one of the 6 MOSFET dis not get hot and burnt the board, it may mean that the other 5 LED strings may have some shorted out LED so the Vdrops on those 5 MOSFETS' have gone up so more power dissipation. I would check the total Vf of each LED string to see what you have which mean you will need LED tester that will show the Vf of each LED string.
      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

      Comment

        #4
        Re: m471i-a2 no backlight

        Shopjimmy has your board in stock for $24 if bad LEDs is not the cause.

        Comment

          #5
          Re: m471i-a2 no backlight

          Thanks for the replies,

          I looked at shop jimmy but the board they have in stock is 1A1 and mine is a 1B1. Is that a compatible board? The reason I asked about the components is that when I was checking it out two of them are cracked. If the board is compatible I will be going with that option.

          Thanks

          Comment

            #6
            Re: m471i-a2 no backlight

            So I have replaced the power board and now some of the led's do not work leaving bright and dim spots on the screen. I have tried to find the whole strip but have not had any luck. Can someone point me in the right direction to buy replacement led's for this model?

            Comment

              #7
              Re: m471i-a2 no backlight

              I ended up soldering on new led's for the ones that had gone out. Has been working since.

              Thanks

              Comment

                #8
                Re: m471i-a2 no backlight

                OK, just got this same model of TV for free, no remote yet. Turns on, but counting from the bottom, I saw only the 2nd of 6 LED strings turning on. Opened it up, and on the power board, looking at the 6 MOSFET's in the OP's photos, the 2nd one is the only one not burned. If I understand budm's post correctly, does this mean the LED strings failed and took the MOSFET's out with them, now necessitating simultaneous replacement of the LED strings and the power board? Or should I try replacing only the power board? Thanks in advance.

                Comment

                  #9
                  Re: m471i-a2 no backlight

                  I think Budm said that failing leds on each string caused the mosfet associated with that string to overheat.
                  Willing to help but I'm no expert.

                  Comment

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