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    #1

    LG 50PG20/UA Shuts off

    Hello everyone,

    I'm in need of help trouble shooting this television set. It turns on for a moment but then shuts back down leaving on the stand by light. No sound or anything, the set just goes off. Naturally I suspect the power board. However this is the first plasma set that I mess with, having only done LCDs and other types of electronics before. That being said I have little knowledge on the different modules and their purposes in the set/involvement in known problems.

    So before buying or trying to repair the power board I wanted to check around here if these symptoms sound like they could possibly come from either the y sustain or z sustain boards, or any other part of the set.

    So far I checked out all the fuses I could find and they all check okay. Next I went to checking the capacitors on the power board and found 4 3300uf capacitors checking high at about 4200uf. Somehow it seems unlikely to me that these are at fault for the sets malfunctions but I guess they could be.

    Thanks for any help you can offer!
    -Carlos
    Tags: None
    #2
    Re: LG 50PG20/UA Shuts off

    Originally posted by FelixTheHouseFreak View Post
    I'm in need of help trouble shooting this television set. It turns on for a moment but then shuts back down leaving on the stand by light....
    First port of call is to check the PSU. Look at the top of the caps and if there's any bulging ones. Although remember that a faulty cap might not necessarily show any signs of degradation.

    If the caps are fine then it's likely that the PSU is shutting down to protect itself and further damage to the TV. I'd start by removing the power to either the Y or Z sustain board then powering up the TV. The idea is to check which sustain board is shorted and shutting down the PSU. These are the easy checks.

    Before you do anything though, take a few 'focused' pictures and upload them here.
    Last edited by Remeniz; 02-02-2011, 02:41 PM.
    Soundcraft CPS-450 and CPS-550 (Rebuilds - Completed!)
    Samsung PS42V6S - in repair (New Y-SUS Board Completed)
    Philips 32PFL7782D/05 - in repair (PSU or Main Board - Selling)

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      #3
      Re: LG 50PG20/UA Shuts off

      Good idea on the disconnecting the other modules.

      There aren't any buldged caps on the Power Supply, I tested them on the meter and as I said I found 4 high 3300uf ones that read somewhere around 4200uf. Haven't finished checking all of them yet.

      Will do on the pics.

      Comment

        #4
        Re: LG 50PG20/UA Shuts off

        Okay, I went ahead and tried the set by disconnecting the Y and Z boards. First tried it with the Z board disconnected, then with the Y board disconnected, then both. In all the tests the set did the same. Comes into standby, push on, turns blue, few seconds, goes back to standby.

        I suppose this means that our problem here is indeed in the power supply somewhere.

        As for the pictures, unfortunately my SD card reader decided to kill itself and I can't post any. I figure it's at least something to post some from around the net. Really it's the same thing since there aren't any tell tale damage signs on any of the boards anyway, and I figure it helps to at least know what they look like.

        Power Supply


        z sustain


        Y sustain



        Here is the info on these modules:

        LG EBR50038903 Y Sustain
        BOARD: 50G1A_YSUS
        PART No:EX50049001

        LG EBR50044803 Z Sustain
        BOARD: 50G1A_Z
        PART No: EAX50053601

        LG LPX55 Power Supply
        LGE P/N EAY41360901

        So far I've only come across those 4 high valued caps that are supposed to be 3300uf but are somewhere around 4200uf as possible suspects. I replaced two of them before performing my tests and it didn't make a difference, only did two because I'm out of that value for the time being. So if anyone can offer any tips on what may be wrong or what to check out next on this PS please let me know!

        So far I just need a couple more thumbs up from people here before I go ahead and purchase the power supply, which I'm trying to avoid but oh well if I have to I'll do it.
        Last edited by FelixTheHouseFreak; 02-03-2011, 04:09 PM.

        Comment

          #5
          Re: LG 50PG20/UA Shuts off

          If the p/s shuts off after a couple seconds you can hook up your meter to va then vs and watch for v when powering up the supply.
          That 16 pin ic should control the converter That is what is shutting down the p/s. Check the small capaciters around this ic They help the control ic work properly and could be the problem.
          When the primary is shorted mostly will see a blown fuse. Easy to check rectifier bridge on incoming ac and the mosfets.
          Most likely your problem is in the secondary. Those caps you replaced what was the v? You should replace all 4 just replaceing two will not help. I have seen these fail on other p/s.
          Check the transisters next to that secondary transformer they look a bit close and take on a lot of heat.

          If all of your output volts are correct when turning on the p/s (before going into protect mode) then check out the control ic and surrounding curcuits (caps)

          I hope this helps a bit. I am still learning about these power supplies.

          Comment

            #6
            Re: LG 50PG20/UA Shuts off

            Cadiman thank you for your tips, I'll see what I can do, if not I guess I'll just buy the entire board.

            Comment

              #7
              Re: LG 50PG20/UA Shuts off

              I have another question.

              As mentioned before I did the test where I disconnected both the Y and Z boards to cancel them out as the fault. First I did the test by disconnecting one then the other. In both power ups the set shut off like always. Then I did another test with both disconnected and it acted the same.

              Now this seems reason enough to rule out the Y and Z boards as the problem. However let's say they both WHERE defective, with one or both unplugged would the power supply power up normally?

              In other words, is there normally any protection circuit that detects when one of the two boards is not present and shuts down the powers supply? If this where the case it would not be possible to figure if one of the two boards was at fault via this method because then every time the power supply would just be shutting off due to the boards being missing and you would not be able to tell whether it was doing that because of a missing board protection or because the power supply is actually bad.

              I hope what I'm trying to communicate makes sense..

              Thanks for any advice. I just want to double check before I order any new parts.

              Comment

                #8
                Re: LG 50PG20/UA Shuts off

                You should check all those caps on the power supply for bulging before you start playing around with the other boards. I have repaired a similar power supply that had bad capxon caps and a bad mosfet.

                -Ben
                Muh-soggy-knee

                Comment

                  #9
                  Re: LG 50PG20/UA Shuts off

                  Ben, as mentioned earlier there were no buldged caps, I've also tested all of the electrolytic caps on the board and found a few high ones. However something tells me that wouldn't be enough to cause this problem.

                  I just finished testing all the semiconductors mounted on the big heat sinks and found no bad ones.

                  Comment

                    #10
                    Re: LG 50PG20/UA Shuts off

                    Dumb thought:

                    Check for a blown/shorted audio output IC.

                    Found one in a hitachi 42EDT20. chased my tail going through everything. IT would NOT let the Vs/Va come up, thinking it was a power supply issue, even with sustain boards unhooked, same deal.

                    swapped power supply, same deal, so i thought, wait a second. removed the cable to the audio output board. bingo. powered up with perfect picture. lol.

                    Removing the heatsink to expose IC404, reveled a huge burned/melted mess. the IC is blown, and some associated transistors were smoked. so yea... just goes to show.

                    Comment

                      #11
                      Re: LG 50PG20/UA Shuts off

                      What are your voltages (Vs, Va, etc.) with all boards connected?

                      Comment

                        #12
                        Re: LG 50PG20/UA Shuts off

                        I have had the panasonic plasmas with mosfet driven driver boards and I could not unplug any boards (the tv would just be dead). I could however unplug a buffer board and then the set fired up. When the large caps on the panasonics fail on the secondary side of the power supply the board just goes into protect mode.

                        I have not worked on any L/Gs with mosfet driven y and z driver boards so I am not sure how to do a quick diag on them like the others. I am hoping to get some soon.

                        You need to find a training manual for this tv.

                        Comment

                          #13
                          Re: LG 50PG20/UA Shuts off

                          Sorry to take so long to get back but I get really busy sometimes.

                          I was wondering if it was possible to measure any voltages with no other board attached to the power board.

                          By the way here is the service manual for reference and/or incase someone just happens to need it.

                          http://www.megaupload.com/?d=9VES158J

                          Comment

                            #14
                            Re: LG 50PG20/UA Shuts off

                            Originally posted by FelixTheHouseFreak View Post
                            Sorry to take so long to get back but I get really busy sometimes.

                            I was wondering if it was possible to measure any voltages with no other board attached to the power board.

                            By the way here is the service manual for reference and/or incase someone just happens to need it.

                            http://www.megaupload.com/?d=9VES158J
                            I'm not sure about this power supply, but on some you can apply 3V to the Power On line and turn the power supply on that way. I'm a lot more comfortable doing this if I put a load on some of the outputs.

                            PlainBill
                            For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                            Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                            Comment

                              #15
                              Re: LG 50PG20/UA Shuts off *FIXED*

                              Sorry I forgot to update this thread.

                              The TV was fixed by replacing the power supply. After just sort of going "screw it" and testing almost every semiconductor and cap on the board I quit and bought the power supply in its entirety.

                              I decided to update this because it's always good to do so as it can help people roaming the internet to gather yet more knowledge and clues as to what their problem is, when they have information on what fixed it for someone else. Wish I could edit the first post so I could update the channel but for some reason it doesn't seem like we're allowed to do that? That's weird.

                              So if you have similar problems as described in this thread do watch out for the power supply.
                              Last edited by FelixTheHouseFreak; 05-25-2011, 03:24 AM.

                              Comment

                                #16
                                Re: LG 50PG20/UA Shuts off

                                Hi, i need help too. having similar problem, turn on tv, & shortly shut off. and the ps board just makes flicking sound. i disconnected the Y & Z board & even both, it shut off shortly & make that sound again. so i believe the ps board is bad. is this correct. thanks for helping
                                Last edited by Seeyah1; 07-06-2011, 05:23 PM.

                                Comment

                                  #17
                                  Re: LG 50PG20/UA Shuts off

                                  Originally posted by Seeyah1 View Post
                                  Hi, i need help too. having similar problem, turn on tv, & shortly shut off. and the ps board just makes flicking sound. i disconnected the Y & Z board & even both, it shut off shortly & make that sound again. so i believe the ps board is bad. is this correct. thanks for helping
                                  That's the usual troubleshooting approach. If the power supply does not provide proper output voltages with both sustains disconnected, it is bad.

                                  PlainBill
                                  For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                                  Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                                  Comment

                                    #18
                                    Re: LG 50PG20/UA Shuts off

                                    Hi, This message is for FelixTheHouseFreak. I know this thread is over a yaer old,but thought I would try to contact Felix.I need the manual that you gave the link to. It appears you can't access this link anymore. If you have a PDF file of this manual,I would appriciate a copy. I have the same issue with my tv and it is the same model 50PG20-UA. I hope you had a Merry Christmas. Thanks, Buzz

                                    Comment

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