50" Samsung Plasma (model number PS50Q91HD) - possible purchase

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  • psmedley
    Senior Member
    • Apr 2012
    • 144
    • Australia

    #1

    50" Samsung Plasma (model number PS50Q91HD) - possible purchase

    Hi All,

    Considering bidding on the subject TV - description of fault is:
    - No Longer Working, (Clicks when turning on and off)

    From what I can find searching - this could either be a bad sustain board, or a problem with the power supply itself, but should definitely be repairable.

    Thoughts?

    Cheers,

    Paul
  • tom66
    EVs Rule
    • Apr 2011
    • 32560
    • UK

    #2
    Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

    Sustain board, probably. I had a PS42C450 which clicked on and off - shorted X-main board - cost £16 for a replacement.

    You've been bitten by the repair bug!
    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

    • tw2005
      Badcaps Legend
      • Oct 2011
      • 6458
      • Australia

      #3
      Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

      Originally posted by psmedley
      Hi All,

      Considering bidding on the subject TV - description of fault is:
      - No Longer Working, (Clicks when turning on and off)

      From what I can find searching - this could either be a bad sustain board, or a problem with the power supply itself, but should definitely be repairable.

      Thoughts?

      Cheers,

      Paul
      I'll go with pwr board. Fixed one of these recently with bad solder joints on a row of transistors attached to long heatsink. Symptoms were randomly shuts off, repeated cycling of the pwr board relays with unit not powering on. seems to be a very common fault with this series from what I'm seen with the broken sets advertised.

      Comment

      • psmedley
        Senior Member
        • Apr 2012
        • 144
        • Australia

        #4
        Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

        Got the TV - probably paid too much ($A101), but Tom66 is right - I've been bitten!!!

        Pictures of board layout attached.

        Will get closeup photos of the boards once I can get some decent lighting.

        Initial observations:
        - when connecting power, clicking noise from the PSU, repeats every 10-15 seconds.
        - disconnect Y-main board from PSU - same
        - disconnect X-main board from PSU - same
        - disconnect board behind main board (Z-main?) from PSU - same
        - disconnect board that runs across bottom of TV - same
        - disconnect all boards except main board - same

        Suggests a PSU issue?

        I do note that there are 2 25v 68uF Samwha's on the Y-main, and 1 x 25v 680uf Samwha on the X-main that are clearly bulged.

        PSU caps are Samyoung

        More to come - but I'll probably test all caps on the PSU with my ESR meter and check for dry joints next. Might not be until the weekend tho.
        Attached Files
        Last edited by psmedley; 06-14-2012, 01:43 AM.

        Comment

        • psmedley
          Senior Member
          • Apr 2012
          • 144
          • Australia

          #5
          Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

          Have found several badcaps on the PSU: - photo attached - will try get a clearer one tomorrow in daylight
          50v 47uf with 0.6 ohms ESR vs reference value of 0.5
          25v 200uf with 0.34 ohms ESR vs reference value of 0.23
          50v 100uf with 0.84 ohms ESR vs reference value of 0.31
          50v 47uf with 0.84 ohms ESR vs reference value of 0.5
          50v 47uf with 1.01 ohms ESR vs reference value of 0.5
          25v 1000uf with 0.21 ohms ESR vs reference value of 0.08
          25v 1000uf with 0.17 ohms ESR vs reference value of 0.08
          50v 47uf with 0.91 ohms ESR vs reference value of 0.5
          25v 220uf with 0.56 ohms ESR vs reference value of 0.23

          Not sure about the following as I don't have reference values:
          100v 820uf with 0.05 ohms ESR vs reference value of ??? - guessing from table between 470 & 1000 uF I'd say reference should be 0.05-0.06 so borderline??
          10v 2200uf with 0.06 ohms ESR vs reference value of ??? - guessing OK? 10v 1000uF has ref of 0.12, 4700uF has reference of 0.23 - this is lower than both
          10v 2200uf with 0.06 ohms ESR vs reference value of ??? - guessing OK?

          big caps:
          250v 820uf with 0.13 ohms ESR vs reference value of ???
          450v 270uf with 0.18 ohms ESR vs reference value of ???
          450v 270uf with 0.17 ohms ESR vs reference value of ???
          Attached Files
          Last edited by psmedley; 06-14-2012, 03:55 AM. Reason: add photo

          Comment

          • tom66
            EVs Rule
            • Apr 2011
            • 32560
            • UK

            #6
            Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

            All caps look okay (typically ESR is higher for small can sizes) but if you want it to last, I'd replace most of the >470uF ones. The 450V, 250V and 100V can stay.

            The problem is probably the cold joints as tw2005 mentions... http://www.youtube.com/watch?v=-Ya8zJMShcs

            Check though if it powers on with either sustain disconnected.
            Last edited by tom66; 06-14-2012, 04:59 AM.
            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

            • tw2005
              Badcaps Legend
              • Oct 2011
              • 6458
              • Australia

              #7
              Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

              I've marked the heatsink that I reflowed on the one I fixed. I could get it to work/fail by applying pressure with a wooden spoon. It could be live! Can't remember now.

              I'd reflow that first. I was at a lady's house picking up another broken set whan she mentioned she also had the same model doing the same thing but she had 5yr wty. The PSU literally went up in smoke whilst she showed me when it cycled a couple of times!
              Attached Files
              Last edited by tw2005; 06-14-2012, 09:55 AM.

              Comment

              • psmedley
                Senior Member
                • Apr 2012
                • 144
                • Australia

                #8
                Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                Originally posted by tom66
                Check though if it powers on with either sustain disconnected.
                I disconnected all boards other than the input/main board and the behaviour was the same. So either the input/main board is the problem or the PSU (IMHO).

                Will try reflowing the joints tw2005 suggests tonight - off to work now!

                Comment

                • psmedley
                  Senior Member
                  • Apr 2012
                  • 144
                  • Australia

                  #9
                  Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                  OK reflowed joints that tw2005 suggested - also the joints for the parts attached to the LH heatsink - and no change in behaviour....

                  Comment

                  • tw2005
                    Badcaps Legend
                    • Oct 2011
                    • 6458
                    • Australia

                    #10
                    Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                    Originally posted by psmedley
                    OK reflowed joints that tw2005 suggested - also the joints for the parts attached to the LH heatsink - and no change in behaviour....
                    Well that's a bugger. Maybe it's blown then. The only other PSU I've had to fix in a plasma was a Panasonic with a blown MOSFET. It continuously clicked because obviously the PSU was not starting up due to the dead switching transistor.

                    Time to follow the circuit and fault find the components I guess or find a cheap PSU.

                    Not cheap new.

                    http://www.electronicsmarket.com.au/...c1-p-6698.html

                    Comment

                    • tom66
                      EVs Rule
                      • Apr 2011
                      • 32560
                      • UK

                      #11
                      Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                      I would begin by checking all supply voltages across the board, seeing if any are obviously wrong. Replace all startup caps too.
                      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

                      • psmedley
                        Senior Member
                        • Apr 2012
                        • 144
                        • Australia

                        #12
                        Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                        Startup caps would all be on the hot side of the PSU?

                        I also see some repair kits on ebay, that suggest checking QX801 or QX802 S/C. (if these are okay then check QS801 and QS802 for S/C. I will look into this later today.

                        Will also try and check voltages - unfortunately there don't see to be too many voltages labelled in order to verify they are correct

                        Comment

                        • tom66
                          EVs Rule
                          • Apr 2011
                          • 32560
                          • UK

                          #13
                          Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                          Originally posted by psmedley
                          Startup caps would all be on the hot side of the PSU?

                          I also see some repair kits on ebay, that suggest checking QX801 or QX802 S/C. (if these are okay then check QS801 and QS802 for S/C. I will look into this later today.

                          Will also try and check voltages - unfortunately there don't see to be too many voltages labelled in order to verify they are correct
                          Yep startup caps on the primary. The voltages are usually 5.2/5.3V standby, 5.2-5.4V run and 18V audio plus normal plasma voltages of 50-70Va and 170 - 210Vs.
                          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

                          • psmedley
                            Senior Member
                            • Apr 2012
                            • 144
                            • Australia

                            #14
                            Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                            found this too: http://img249.*************/img249/8...10127at184.png
                            which shows voltages.. not where to check them but at least its a start

                            Comment

                            • tom66
                              EVs Rule
                              • Apr 2011
                              • 32560
                              • UK

                              #15
                              Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                              SM:

                              Pin outs for PSU connectors are on page 40.
                              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

                              • psmedley
                                Senior Member
                                • Apr 2012
                                • 144
                                • Australia

                                #16
                                Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                                Thanks Tom - will investigate more and report back later after dog walking, etc

                                Also, given all the repair kits mentioning shorted mosfets, looking for good ways to test them for shorts - preferably in-circuit (if possible).

                                Comment

                                • tom66
                                  EVs Rule
                                  • Apr 2011
                                  • 32560
                                  • UK

                                  #17
                                  Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                                  Just check all pins relative to each other; should measure >200 ohms.
                                  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

                                  • psmedley
                                    Senior Member
                                    • Apr 2012
                                    • 144
                                    • Australia

                                    #18
                                    Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                                    Originally posted by tom66
                                    I would begin by checking all supply voltages across the board, seeing if any are obviously wrong. Replace all startup caps too.
                                    On CN801 - the connector to the input board, I measure the following:
                                    STDBY 5v = 5.09V
                                    5v = 0.69v
                                    12v = 0.83v
                                    18V = 0.83v

                                    This is with CN801 unplugged. In this condition there is no clicking from the PSU

                                    Comment

                                    • psmedley
                                      Senior Member
                                      • Apr 2012
                                      • 144
                                      • Australia

                                      #19
                                      Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                                      I read that if a mosfet is dead, they often short from drain to gate.

                                      This seems to be the case here - I have continuity (< 3 Ohms) between drain and gate on QS801 & QS802, but not with QX801 and QX802
                                      Last edited by psmedley; 06-15-2012, 06:37 PM.

                                      Comment

                                      • psmedley
                                        Senior Member
                                        • Apr 2012
                                        • 144
                                        • Australia

                                        #20
                                        Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

                                        Photos of front/back of PSU board - hopefully there was enough light left that these are sharp enough!

                                        Also just confirmed that fuse F803 is blown, but there is still continuity through the terminals - I guess because QS801/802 are shorted?
                                        Attached Files
                                        Last edited by psmedley; 06-16-2012, 01:23 AM.

                                        Comment

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