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    Samsung plasma PN51D550 "red mist" pixels

    Alright. I've been trying to chase one thing after the other, combing the forums for some clues, but I'm over my head (which isn't difficult to achieve, sorry to say).

    I acquired a Samsung PN51D550 that did the usual 6 blinks, no turn on. I didn't hear startup audio, as once I fixed it, found the previous owner had disabled the internal speakers. I would get Vs and Va ramp up and drop on turn on, with the slow LED blink.

    I disconnected the Y-sus from SMPS (and associated cables to the X-main as well), and was able to get stable voltages on the SMPS, and a "normal" pulse from the Logic LED. A quick check of the X-main IC's found the usual compliment of shorts (on ALL the transistors), so I found a replacement and ordered it. While waiting, I checked the Y-sus for shorts and didn't see anything too far out of the ordinary, so I kept it. I don't want to throw lots of $$ at the tv, as I'm repairing this for a young friend w/out lots of $$.

    So, new X-main is in, the tv powers on and shows a picture. I was able to set the following:

    Vs- 203 Vdc (spec)
    Va- 58 Vdc (spec, but found later could only maintain after running for a bit)
    Vsc - -193 Vdc (spec)
    Ve - 84.3Vdc (lowest I could get it, spec is 83)

    I noticed Ve was too high, and since the Ve voltage is supplied by the Y-sus, someone asked me to measure that. Y-sus is supplying 105.3Vdc over to the X-main. On top of this, I'm getting red pixilation on mainly white/light screens, and am not sure if it is associated with the increased Ve voltage.

    Other forums said to work with contrast/brightness and other color adjustments, but it didn't seem to make much difference unless I brought the values so low as to make watching difficult. I tried to increase the Vs a bit (to 205Vdc) just to see if it would clear up the spots, but it didn't do much, and I've read enough to know that it's not good for the set to leave it like that for too long. I also read a post mentioning to raise the Vsc to see if it would help, and it didn't.

    My questions are whether anyone knows what would make the Ve run on the high side (and is it a problem)? Would it be a possible cause of the "Red mist" (as I'm calling it) on white screens? And if not, where should I start looking to fix the patches of red pixels?

    I've attached pictures of the back of the set, along with what will hopefully show the red patches I'm trying to describe! Even if someone could point me to a previous post I may have overlooked, I'd be appreciative!
    Attached Files
    Last edited by ranergeo; 03-02-2018, 02:01 PM.

    #2
    Re: Samsung plasma PN51D550 "red mist" pixels

    This looks like the problem Samsung had w the 7000 and 8000 C series. Which was corrected by raising VS up about 5 to 8v.
    Last edited by freakaftr8; 03-02-2018, 02:22 PM.
    Did I leave the soldering iron on?

    Comment


      #3
      Re: Samsung plasma PN51D550 "red mist" pixels

      The logic board does not have a good algorithm to base against aging of the panel.

      Do you notice this on darker scenes or only white? And the X main should have a VE trim pot.
      Last edited by freakaftr8; 03-02-2018, 02:23 PM.
      Did I leave the soldering iron on?

      Comment


        #4
        Re: Samsung plasma PN51D550 "red mist" pixels

        I did try raising the Vs about 5v (along with the Vsc) without much success, and I only notice this with white screens/scenes mainly. I watched a movie online earlier, and didn't notice much during the med/dark scenes, or scenes where there was a lot going on.

        There is a Ve trim pot, but the lowest I can get it to go before it stops is 84.3v... I can get plenty more above that (but don't think it will help, as if I remember reading somewhere, its responsible for turning things off??)!

        I also updated the firmware to the latest and greatest, as other posters mentioned it was ABSOLUTELY(!) necessary with this series of Samsung if I didn't want to lose my X-main again (which is why the high Ve concerns me).
        Last edited by ranergeo; 03-02-2018, 03:32 PM.

        Comment


          #5
          Re: Samsung plasma PN51D550 "red mist" pixels

          Ve is an unregulated supply, generated off the transformer that makes Vsc. Not much you can do to adjust it. However it will not substantially affect the lifespan of the X-main, because it is only used by the Ve bias part of the circuit, not the main sustain panel current drive (considerably less current than it).

          You can try increasing -Vsc to around -210V to see if that helps resolve the issue.

          If there are Yfr or Yrr pots on the board then you may be able to adjust those as well.
          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 plasma PN51D550 "red mist" pixels

            Thanks for the Ve info!

            I turned up the Vsc as high as it would go and max'd out at 206.6v. I've attached pictures from a SVC menu test pattern scrolling across the screen. I still get the haze, but it moves with the white (or whatever that range is on the screen, so it seems to be a firing issue and not a screen issue?) I also notice some green dots on the black scene, like the good 'ol green/red sparkle days!

            Speaking of which, I do have an adjustment for Yfr, but thought I needed an oscilloscope to adjust this (unless I do the "turn a bit and hope for the best" adjustment, lol!)?

            On a related note, while in the SVC menu, noticed the tv does have 14.5k hours on it, so I'm guessing it's a wee bit tired...

            EDIT: 1st and 3rd pics are the scrolling red mist lines, second pic was me trying to capture the static green dots on the black portion

            EDIT: Could the "new" x-main be the issue (and if it's a possibility, what would I test?)?
            Attached Files
            Last edited by ranergeo; 03-03-2018, 07:14 AM. Reason: More questions popped up

            Comment


              #7
              Re: Samsung plasma PN51D550 "red mist" pixels

              Follow Up: Went through ALL the factory service test patterns, and the "red misting" doesn't show on anything but a white screen that stretched fully horizontal. It didn't how at all with the slow vertical white band sweep from left to right or any of the other colors.

              I also did find the Yrr, so I'm going to find the thread on how to best adjust them without a scope and report back later!

              Comment


                #8
                Re: Samsung plasma PN51D550 "red mist" pixels

                also mark the adjustment pots with a marker pen first so you can return them too the original spots if needed.

                Comment


                  #9
                  Re: Samsung plasma PN51D550 "red mist" pixels

                  why didn't i think of that!

                  Thanks!

                  Comment


                    #10
                    Re: Samsung plasma PN51D550 "red mist" pixels

                    i would just mark the pot and turn it down a bit check picture if worse turn up a fraction and check picture but i guess the risk is if go up too high by mistake and blow parts maybe tom66 will advise what you can do adjustment wise without a scope.

                    Comment


                      #11
                      Re: Samsung plasma PN51D550 "red mist" pixels

                      I may wait to grab a scope from work, although I must admit I've not yet tried adjusting rising/falling ramps on the y-sus with one as of yet... I'd also need to find what the pattern should look like. The last t.v. I needed to do this on was a 2008 Sammy, and I only did small incrementals until I was rid of the sparkles

                      Comment


                        #12
                        Re: Samsung plasma PN51D550 "red mist" pixels

                        Look for a firmware update too address this problem. May be a logic board issue. Like I said, the C series had this problem. An update via Samsung website fixed 95% of the issues. The algorithms were updated to address aging panels.
                        Last edited by freakaftr8; 03-03-2018, 01:57 PM.
                        Did I leave the soldering iron on?

                        Comment


                          #13
                          Re: Samsung plasma PN51D550 "red mist" pixels

                          maybe this firmware it says makes improvement on sd picture
                          https://www.samsung.com/us/support/o...ma-tv-5-series

                          Comment


                            #14
                            Re: Samsung plasma PN51D550 "red mist" pixels

                            Thanks Freak and Vince! One of the first things I did after replacing the x-main was to locate an update. At first, the file from Samsung wouldn't load, later to find that someone had already put the 1019 update in, however, I was able to find a 1019.5 update from another poster who had received one directly from Samsung. Even after applying that patch, nothing seemed to change :-/

                            I'm thinking the 14,500 hrs on the panel might finally be catching up to it...

                            Comment


                              #15
                              Re: Samsung plasma PN51D550 "red mist" pixels

                              Originally posted by vinceroger69 View Post
                              i would just mark the pot and turn it down a bit check picture if worse turn up a fraction and check picture but i guess the risk is if go up too high by mistake and blow parts maybe tom66 will advise what you can do adjustment wise without a scope.
                              Won't blow anything.

                              Worst case is you go "too bright" and trigger a shutdown. On some LG plasmas it would cause the panel to draw a lot of current which caused the SMPS to shut down. But no harm to sustain drivers, as only for short period of time.

                              Just adjust carefully, note position using marker pen as mentioned above, and see what happens.

                              Scope would be ideal, but you can still tweak without one.
                              Last edited by tom66; 03-03-2018, 05:49 PM.
                              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 plasma PN51D550 "red mist" pixels

                                Tom, thanks for the clarification! I believe you mentioned starting with the YRR, but I'll look back and check...

                                Quick question tho... if I were to use a scope on the YRR/YFR, what would I be looking for patter-wise? I remember seeing the pattern in an older plasma manual I once had, but the one for this model doesn't have one shown. Also, is it simply a 2 channel trace between the YRR/YFR and ground?

                                I'll see what I can locate in the threads in the meantime, but they're getting pretty expansive!

                                Comment


                                  #17
                                  Re: Samsung plasma PN51D550 "red mist" pixels

                                  I don't know what you mean by two-channel trace.

                                  Yrr and Yfr adjust the ramp timing. Picture (from LG, but Setup and Setdn are similar to Yrr and Yfr):

                                  http://4.bp.blogspot.com/-8RDK8j1TqP...600/fig-11.jpg

                                  This adjusts the way that the panel initialisation ramp is applied, which determines how the gas in the panel will discharge.

                                  If the settings are wrong it can cause panel maldischarge.
                                  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 plasma PN51D550 "red mist" pixels

                                    Thanks! That helps explain it much better! I'll grab a scope from work on Monday, since we use them to test car electronics periodically. Sorry, "trace" is used by one of our manufacturers to refer to the lines the scope can produce over a channel, and I originally thought I would need to trace BOTH yrr and yfr individually. However, the post you sent shows a single form with both patterns. I'll try to clean up my terminology in the future

                                    Thanks again for the help, I'll post back once I give the ramp adjustments a try!

                                    Comment


                                      #19
                                      Re: Samsung plasma PN51D550 "red mist" pixels

                                      Make sure to get minimum 10x probes with the scope. You are probing signals with a voltage amplitude of over 500V peak to peak, +300V to -200V typically.
                                      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 plasma PN51D550 "red mist" pixels

                                        So I decided to simply go ahead and try tweaking the yrr and yfr by getting a factory test pattern up that showed some red misting on the white and green pixelization on the black.

                                        Going by Tom66's recommendation, started with yrr and made small increments either way (after marking the pot first). I noticed no discernible change in picture quality, but found the pot to already be in the full clockwise position. I'm not sure if that's low or high voltage without looking at a scope, but it's something I noticed.

                                        I then tried to adjust the yfr, and again didn't see any great change as I slowly moved the adjustment.

                                        Out of curiostiy, since I ONLY noticed the red mist/green dots on two of the 25 test patterns (only the black to white gradient screens), I decided to again test a normal signal through the tv. First test was a stand up comedian on stage... lots of black in the background. No green dots. Next I ran a show with lots of brightness and whites, and again, no "red mist" is showing on the screen! I'm still running the Vs about 5v higher thn specified, but everything else is on spec (aside from the still-too-high Ve on the x-main)

                                        I'm not sure why I'm now only seeing the issue on a couple of test patterns, but I'm thrilled that its working!

                                        If anyone has any thoughts as to why this might be the case, I'd love to hear them!!

                                        However, I'm thinking this set is done, as I just got my hands on a bigger problem child... a Sammy PN51F8500... with power off/on issues and slow to fill pixels when it is working. I hear the picture is beautiful when it's working ;-)

                                        Thanks again everyone for the help!

                                        Comment

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