LG Plasma 50PG100R Problem

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  • VHSFI
    Member
    • Mar 2011
    • 47
    • Portugal

    #1

    LG Plasma 50PG100R Problem

    Hi,

    I have an LG plasma that has sound but no picture, opened it up and checked voltages and they all seem ok, fuses an all boards are good, i then
    noticed that the Y-sus board wans't getting warm like the other boards on the system.
    Checking voltages across VSC and VS resistors on Y board i got only a few mV.
    I then tried disconnecting the Y-Buffer boards and the results where as follow:

    Without any Y-Buffers boards: VSC & VS on Y-Board Voltages OK
    With only the Top Y-Buffer : VSC & VS on Y-Board mV
    With only the Bottom Y-Buffer: VSC & VS on Y-Board Voltages OK - White Image with noise on about 1/4 screen bottom part

    Now this led me to belive that the y-buffers where bad but i already replaced them and the problem remains.
    Is it the Y-Sus board that is bad?
    Any other diagnostic that i can do?

    Thx in advance for any help

    Vitor Ferreira
  • tom66
    EVs Rule
    • Apr 2011
    • 32560
    • UK

    #2
    Re: LG Plasma 50PG100R Problem

    Can you check the Vs voltage and Va voltage outputs from the PSU? Do the measurements with and without the Y-sustain connected. Don't connect the Y-sustain while the TV is running, you will pop the fuse on the Y-sustain (doesn't usually damage anything but the fuse -- it's just annoying) - unplug the TV and wait 30 seconds before connecting it, then powering it up.

    For an LG "PG" plasma you are looking for (I think) around 180-190V for Vs, and 50-70V for Va, though the newer ones may be different, I have only worked on PC and PX series.
    Last edited by tom66; 10-26-2012, 05:40 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

    • VHSFI
      Member
      • Mar 2011
      • 47
      • Portugal

      #3
      Re: LG Plasma 50PG100R Problem

      Checked the voltages on the PSU

      With Y-Sus connected:
      Vs: 194.5
      Va: 59.6

      Without Y-sus connected:
      Vs: 194.4
      Va: 59.9

      There is a sticker on the back of the panel with the reference voltages:
      Vs - 194v / Va - 60v

      Comment

      • tom66
        EVs Rule
        • Apr 2011
        • 32560
        • UK

        #4
        Re: LG Plasma 50PG100R Problem

        OK, your supply voltages are good, and well matched with the sticker.

        Can you post a picture of your Y-sustain - some other checks can be done.
        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

        • VHSFI
          Member
          • Mar 2011
          • 47
          • Portugal

          #5
          Re: LG Plasma 50PG100R Problem

          Sure thing, sry about the quality
          Attached Files

          Comment

          • tom66
            EVs Rule
            • Apr 2011
            • 32560
            • UK

            #6
            Re: LG Plasma 50PG100R Problem

            Tiny gold plated fuse by the ribbon cable - is this OK?

            Check for Vs on both ends of fuse - should be the same.
            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

            • VHSFI
              Member
              • Mar 2011
              • 47
              • Portugal

              #7
              Re: LG Plasma 50PG100R Problem

              Fuses are ok,

              The mini fuse to the right of ribbon cable reads 59.7V, the one to the left 4.95V
              the normal fuse near the cable that comes from the PSU reads 194.5V, all read the
              same on both ends.

              Comment

              • tom66
                EVs Rule
                • Apr 2011
                • 32560
                • UK

                #8
                Re: LG Plasma 50PG100R Problem

                The Vs drops to zero when your original top buffer is installed?

                But you got some light from the plasma panel when you installed only the Y bottom buffer, so your Y-sustain is probably OK. (It is only responsible for making the screen light up; with only one buffer installed sometimes you'll get half a picture, other times you'll get noise.)

                I am suspicious your replacement top buffer may be faulty.
                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

                • VHSFI
                  Member
                  • Mar 2011
                  • 47
                  • Portugal

                  #9
                  Re: LG Plasma 50PG100R Problem

                  I remade the measurement's across the resistors in the Y-sus board

                  No Y-Buffers attached
                  VY - 195.6V / VSC - 135V

                  Both Y-Buffers attached
                  VY- 116mV / VSC - 6mV

                  Bottom Buffer Only
                  VY- 195.6V / VSC - 134.9V and bottom light of the screen light up

                  These results are the same with both the original and the replacement Y-Buffers.

                  The VY / VSC voltages of 195 / 135 match exactly the ones on the sticker in the panel.
                  My problem is what's odds of getting exactly the replacement top Y-Buffer damaged.
                  Any way to do some poke around in the Y-Buff to check for something bad.
                  Sourcing these parts was already a pain, i'm kind of afraid of getting another pair and
                  having the same result.

                  Comment

                  • tom66
                    EVs Rule
                    • Apr 2011
                    • 32560
                    • UK

                    #10
                    Re: LG Plasma 50PG100R Problem

                    Here is how to test the buffers:

                    http://blog.coppelltvrepair.com/2010...-lines-in.html

                    (regarding older plasma but the testing advice for the buffers is the same.)
                    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

                    • VHSFI
                      Member
                      • Mar 2011
                      • 47
                      • Portugal

                      #11
                      Re: LG Plasma 50PG100R Problem

                      Just a bit of help as my Y-buffers are a bit different from those in the site, are these the correct spots to test with the DMM?
                      Attached Files

                      Comment

                      • tom66
                        EVs Rule
                        • Apr 2011
                        • 32560
                        • UK

                        #12
                        Re: LG Plasma 50PG100R Problem

                        Those look like the right places.
                        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

                        • VHSFI
                          Member
                          • Mar 2011
                          • 47
                          • Portugal

                          #13
                          Re: LG Plasma 50PG100R Problem

                          Doing the diode test shows 0.068V on both positions, the bottom ones show 0.531V on one position and OL in the other, so i guess the top ones are busted.
                          Do you know any reliable place that ships to europe?

                          Comment

                          • tom66
                            EVs Rule
                            • Apr 2011
                            • 32560
                            • UK

                            #14
                            Re: LG Plasma 50PG100R Problem

                            I have used flattvparts.co.uk before. Their prices are generally low, but they are often out of stock, possibly because their prices are low...!

                            Both the buffer outputs are shared on most plasmas. So if one is killed by the Y-sustain, the other should be too. It is possible (though very rare) that the plasma panel has an internal short circuit between some lines on the screen which has damaged the buffer.

                            If you are brave you can attempt to find which buffer chip is failed but you will need a high current DC power supply. If you apply DC to the test points in the direction reading OL on the good buffer (tested on the bad one of course) you will find the failed chip will get hot and maybe even smoke a little. Don't do it for too long of course. If it is failed in the same place for both of them, I would suspect the panel.
                            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

                            • VHSFI
                              Member
                              • Mar 2011
                              • 47
                              • Portugal

                              #15
                              Re: LG Plasma 50PG100R Problem

                              So what you are trying to say is that as the bottom Y-Buff seem to be ok, the cause of the problem maybe from the Panel itself, and not from the Y-sus as if that where the case it would most likely blow both of the Y-buffs.

                              Comment

                              • tom66
                                EVs Rule
                                • Apr 2011
                                • 32560
                                • UK

                                #16
                                Re: LG Plasma 50PG100R Problem

                                That is what I am worried about, because if it is the panel itself, it is pretty much unrepairable. This happens rarely on Panasonic sets, but I have never heard of it on an LG, so I am hoping it was just a defective buffer that you were unlucky enough to get.
                                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

                                • VHSFI
                                  Member
                                  • Mar 2011
                                  • 47
                                  • Portugal

                                  #17
                                  Re: LG Plasma 50PG100R Problem

                                  Panel would be very bad, about that test you mentioned, how much current you think would be needed?

                                  Comment

                                  • tom66
                                    EVs Rule
                                    • Apr 2011
                                    • 32560
                                    • UK

                                    #18
                                    Re: LG Plasma 50PG100R Problem

                                    Heh, what do you have? The buffer is bad, anything more than a few amps will make the chip which is bad go pop. I wouldn't advise a (virtually) unlimited source like a car battery, but it might work if you were vigilent and can unplug it quickly.

                                    If you are good at SMD soldering, you can try transplanting the failed chip for one of the good ones on the bad buffer (only one of the chips under the heatsinks fails usually.)

                                    If the TV was working normally, it is quite rare for the panel to fail randomly. Usually it has to be contamination, which could occur from an impact or drop which didn't break the screen but still did internal damage.
                                    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

                                    • VHSFI
                                      Member
                                      • Mar 2011
                                      • 47
                                      • Portugal

                                      #19
                                      Re: LG Plasma 50PG100R Problem

                                      Well i have a 30v - 5A power supply, also what you say explain perfectly why the replacement is bad as apperently was removed from a tv with a broken panel. Think i might try to see if i can identify the faulty ic.

                                      Comment

                                      • tom66
                                        EVs Rule
                                        • Apr 2011
                                        • 32560
                                        • UK

                                        #20
                                        Re: LG Plasma 50PG100R Problem

                                        I have always suspected that no-one tests these TVs with broken panels. If the panel in the scrapped TV is broken and lines short together... boom, there goes the buffer when plugged in, but you don't see anything on the screen, so you can't be 100% that the buffer is good or not.

                                        30V 5A should do it, just be careful to get polarity right (in direction when you read "OL") or you will blow all 6 or so chips at once .
                                        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

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