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Need help troubleshooting Samsung PN42C450 Plasma

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    Need help troubleshooting Samsung PN42C450 Plasma

    Hey folks, I need some help diagnosing and fixing my tv. It's the above model, assembled Oct 2010.

    The problem started with the typical no picture and clicking noise coming from the set. I changed the y-sus and buffer boards and that didn't fix it so then I replaced the x-main. After that, I had a picture again.

    The instructions with the board said to update the firmware after replacing the x-main board so I did that even though it said I was updating to the same firmware already on the set. It told me the update failed and I thought that made since and didn't think anything of it. I put the back cover back on the set and put it back on the entertainment center after that and after that it wouldn't turn on again.

    So I was left wondering if I bricked something on the logic board with the firmware update? Or did I somehow short something when I was putting the cover back on? Did plugging a HDMI cable in mess up something on the main board? Did the x-main crap out again after one power-cycle and if so, why?

    I've done more testing since then and I think I've only made things worse at this point, but here's what it does now:

    With all the cables plugged in--You hear the relays click a couple of times and the power supply shuts down before the VS and VA can hit their normal levels.
    With x-main unplugged--Relay clicks once and the VS and VA peg their normal levels but then the power supply goes into shutdown mode.
    With y-sus disconnected--same as above

    With the y-sus connected you can see a bit of static appear on the screen for about a second once you hit the power button. The voltages from the output of the y-sus to the x-main match what is printed next to the connector, so do I just assume the x-main board is bad again? Are there any other tests I should do before I replace it again to make sure I don't burn it out if that's what happened?

    I never get the startup chime anymore either, fwiw.

    If you need pictures the 6th post in this thread matches my Tv: https://www.badcaps.net/forum/showthread.php?t=34043

    If you need more, let me know.

    #2
    Re: Need help troubleshooting Samsung PN42C450 Plasma

    Try running the test patterns. Unplug the flat ribbon that goes from the mainboard and the logic control board and short the two pins 3 and 4 If I remember right.

    Comment


      #3
      Re: Need help troubleshooting Samsung PN42C450 Plasma

      I get nothing, it shuts down if I have the x-main connected and when I don't all I get is snow for a second or two. Works the same with the old x-main and the replacement.

      Try replacing that board yet again?

      Comment


        #4
        Re: Need help troubleshooting Samsung PN42C450 Plasma

        Post a pic of the backside ofcthe x main. I bet there are shorted ibgts on it.

        Comment


          #5
          Re: Need help troubleshooting Samsung PN42C450 Plasma

          Not great pictures, hope they're helpful in some way.

          The transistors/diodes mounted to the heatsink are Q4007, Q4002, Q4003, Q4000, D4000, and Q4001 from left to right.

          Positions 1 and 6 are labeled RJH30E2
          Positions 2 and 3 are AUK STK1820 (one has 050819 and the other has 030818, are those date codes?)
          Position 4 says 45G122
          Position 5 AUK 71517 SF10A400H

          I highlighted the pins on one image fwiw.
          Attached Files

          Comment


            #6
            Re: Need help troubleshooting Samsung PN42C450 Plasma

            Check all the transistors. They start with the letter Q. Look for shorted parts. There is a guy on ebay that has one for about $16.

            Comment


              #7
              Re: Need help troubleshooting Samsung PN42C450 Plasma

              Ok, that's where I need some help. Can I test them in circuit?

              Also, is there a simple way to find out which pin is which, or do I need to find data sheets for all of these?

              Comment


                #8
                Re: Need help troubleshooting Samsung PN42C450 Plasma

                Put your meter in diode mode and test the outside legs of the "Q" parts. A beep longer than 3 seconds means it is bad. Remove and test again. You will save time and money by replacing the board, the parts alone will cost $25 or more and you run the risk of receiving fake parts.

                Comment


                  #9
                  Re: Need help troubleshooting Samsung PN42C450 Plasma

                  Ok, ShopJimmy sent me a new board under warranty. Put that in and I still don't get a picture or startup chime, just a hint of snow on the screen for about a second.

                  The power supply does stay on now, however, with proper voltages. VSC on the y-sus board is proper as well. The LED on the logic board blinks once per second. I can turn the tv on with the power button on the front but after that the button becomes unresponsive (can't turn it off that way) and I don't know if the other buttons (source, menu) are working or not.

                  What do I investigate next?
                  Last edited by nrbrandt; 09-26-2017, 07:23 PM.

                  Comment


                    #10
                    Re: Need help troubleshooting Samsung PN42C450 Plasma

                    try doing the test patterns again.
                    WHY CAN'T PHILIPS USE PHILLIPS HEAD SCREWS?

                    Comment


                      #11
                      Re: Need help troubleshooting Samsung PN42C450 Plasma

                      I forgot about those. They do work now, so replace the main/tuner board as well?

                      Comment


                        #12
                        Re: Need help troubleshooting Samsung PN42C450 Plasma

                        Yes.

                        Comment

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