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Samsung PS58C7000YFXXY - Sound but no picture

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    #1

    Samsung PS58C7000YFXXY - Sound but no picture

    Hi Guys. I'm hoping to get some help with my Samsung PS58C7000YFXXY. A few nights ago we lost picture after a small “pop”. It still has sound and like many of these Samsung plasmas had the occasional purple banding on brighter scenes.
    Anyway, I ripped the back off hoping to find burnt remains of something but cannot see or smell anything!
    This TV has the BN44-0034A SMPS and as far as I can tell the TV is going into fault protection as the logic board LED flashing on for 5 seconds.
    Vital Signs.
    The Standby 5v is at 5.23v, and the PS-ON shifts from 3.26v – 0.1v when powered on.
    However Vs-ON shifts from 0v to 3.27v but then back to 0v and stays there. This over the first few seconds the TV is turned on.
    Over the same first few seconds, Vs and Va rise to 209v and 54v respectively, both 1v under the labelled voltage - but then fall back down and settling at 14v for Vs and 1v for Va.
    Fuses on the SMPS, Y-Main, X-Main and one surface mount on the E-Buffer are all ok.
    I believe the SMPS will only fire up briefly if Y-Main and X-Main are disconnected so disconnecting those boards won't help the trouble shooting process. I did confirmed this, the voltage rails have the same behaviour with X and Y Main disconnected.
    Any ideas would be most appreciated and hopefully may help others that find themselves in the Samsung Sound but no Picture Club.
    Tags: None
    #2
    Re: Samsung PS58C7000YFXXY - Sound but no picture

    Did you check y buffer for any sorted ic also check all the mosfet on y sustain

    Comment

      #3
      Re: Samsung PS58C7000YFXXY - Sound but no picture

      Check the Vsc and Ve voltages on both Y- and X-main boards. What does LED on control board do? Flash about once a second, or light up for 2 secs then off for 5 secs?
      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.

      Comment

        #4
        Re: Samsung PS58C7000YFXXY - Sound but no picture

        For reference, on this TV Va=55v, Vsc= -200v, Vs=210v and Ve=90v.

        When the TV is turned on, Vsc (marked Vscan) on the Y-Main holds at -200v for about 10-15 seconds then slowly drops to 0v.
        On the x-Main board, I could only find a test point Vb. That test point reaches 89v for a second then drops to 14.6v.
        The LED on the control board blinks quickly 2-3 times when the TV is turned on but then settles to 5 seconds on, 2 seconds off, 5 seconds on - etc etc.

        I could not identify what lives under the heat sinks on the Y-Main but running the meter over them didn't find any D-G shorts on any would be MOSFET's. A parts list would be handy.
        To make things a bit harder, the Y Buffer board has heat sink pads on the microcontrollers so I cannot see if there is any pinholes/damage. There are no test points for the microcontrollers either or markings on the connectors between the buffers and main boards :-(

        Thanks guys for your input!

        Comment

          #5
          Re: Samsung PS58C7000YFXXY - Sound but no picture

          Are there any cracks on the display panel itself? The smallest crack can trigger this fault.
          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.

          Comment

            #6
            Re: Samsung PS58C7000YFXXY - Sound but no picture

            Ok - I have checked the panel for cracks by using a torch on an angle over the screen but did not see any cracks. Is there a better technique?
            For what it's worth, we had been watch the TV for about 30mins when it stopped. Can the panel crack / fail like this while in use?

            Comment

              #7
              Re: Samsung PS58C7000YFXXY - Sound but no picture

              The panel can crack while running but it's usually obvious.
              Hard to be sure where the fault is, maybe could be bad Y-buffer board. Try checking buffers: https://www.youtube.com/watch?v=51SZsfH60EY
              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.

              Comment

                #8
                Re: Samsung PS58C7000YFXXY - Sound but no picture

                Thanks for the link tom66! I tested the Y-Buffer as shown but no shorts.
                There are no markings on the connectors (see pic) so had to look for groups of pins tied together. There are no test points for the controllers and with heat sinks on top - no damage can be seen either.
                Is it worthwhile poking around on the X-Main? Thanks.
                Attached Files

                Comment

                  #9
                  Re: Samsung PS58C7000YFXXY - Sound but no picture

                  To check the Y-buffer, you'll have to disconnect those ribbon connectors and test around the exposed pins on the connectors.
                  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.

                  Comment

                    #10
                    Re: Samsung PS58C7000YFXXY - Sound but no picture

                    Sorry - it's a picture I took before disconnecting the ribbon connectors - I should have mentioned that...
                    I tested both sides of the connector on the PCB once the ribbon connectors were removed. Not a peep from the meter.

                    Comment

                      #11
                      Re: Samsung PS58C7000YFXXY - Sound but no picture

                      Do you have any access to an oscilloscope?
                      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.

                      Comment

                        #12
                        Re: Samsung PS58C7000YFXXY - Sound but no picture

                        Yes - I have an oscilloscope.

                        Comment

                          #13
                          Re: Samsung PS58C7000YFXXY - Sound but no picture

                          Great, can you supply a photo of it? Do you have a 10X probe? Using the scope, the sustain outputs can be checked to see if the Y-main is properly functioning.
                          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.

                          Comment

                            #14
                            Re: Samsung PS58C7000YFXXY - Sound but no picture

                            Here it is - it's nothing to get excited about but is does work! I also have a 10x probe. The TV does have an earthed ground chassis so no need for an isolation transformer which is good as I do not have one...
                            How / where should I check the sustain outputs? Thanks.
                            Attached Files

                            Comment

                              #15
                              Re: Samsung PS58C7000YFXXY - Sound but no picture

                              That's absolutely fine for this kind of test.

                              Even if the chassis were not earthed, you could do it by connecting your scope ground to the floating chassis. As long as you're not probing the primary of the PSU. Things like the HDMI ports connected to earthed devices (old PS3/Xbox 360 comes to mind, or a PC) would do the same anyway.

                              Can you get a clear photo of your Y-main board? (connects to the Y-buffers you have photographed above)
                              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.

                              Comment

                                #16
                                Re: Samsung PS58C7000YFXXY - Sound but no picture

                                OK, here is the Y-Main. Hopefully it is clear enough. If not I will upload the board spit over two pictures.
                                Attached Files

                                Comment

                                  #17
                                  Re: Samsung PS58C7000YFXXY - Sound but no picture

                                  That's fine. Your probe point is highlighted in red. The ground point is the nearest point on the chassis - that screw hole near to the probe point will work just fine. Do NOT short the output area plane to GND or you will damage something.

                                  Scope should have trace centred, 50V/div (5V/div 10X probe), 5ms/div, AC LINE trigger (for now)
                                  Triggering it is hard with an analog scope, we just want to see if there's any activity
                                  Attached Files
                                  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.

                                  Comment

                                    #18
                                    Re: Samsung PS58C7000YFXXY - Sound but no picture

                                    I finally got a chance to test. We got very brief activity.
                                    I posted 2 links so you could see the result, one at 5ms/div, one at 50us/div, both at 50v/div as suggested.

                                    http://youtu.be/4sg3ScymxNQ

                                    http://youtu.be/61Ky59A7oRA

                                    Comment

                                      #19
                                      Re: Samsung PS58C7000YFXXY - Sound but no picture

                                      Ok, it looks like the Y-main board is briefly working, but the control board is picking up on some fault. Can you try repeating the test on the X-main? Let me know if you need me to highlight the X-main output.
                                      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.

                                      Comment

                                        #20
                                        Re: Samsung PS58C7000YFXXY - Sound but no picture

                                        I have an idea but if you could point it out then that would be great. Thanks.
                                        Attached Files

                                        Comment

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