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LG 50PJ350 plasma blowing Y-Sustain board

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    #41
    Re: LG 50PJ350 plasma blowing Y-Sustain board

    I actually have 2 Y Sustain boards, the original and one that someone gave me that was also in need of repair. I have the exact same symptoms with both boards and also with a 2nd set of buffer boards. So unless both have the same problem, I'm thinking bad panel or Z Sustain. But what I'd like to know is if it's normal for the Sus_Dn section heat sink to run so hot.

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      #42
      Re: LG 50PJ350 plasma blowing Y-Sustain board

      I thought it was only one of the Y boards that was working properly.
      Since it is both of them, discard my previous reply.

      Never saw a bad panel do this, this is some board's doing.

      The Z-sus job is to light up the panel's brightness, it could be messing up the image.
      On repair kits online they include a transformer, the big one on Y board, but if this transformer open any windings the Y-SUS does not work at all.

      Just to be sure, I'll send 2 images with the resistors circled. Also the fuses have to be good too, the big ones for VS, as well as those green and orange ones.
      Attached Files

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        #43
        Re: LG 50PJ350 plasma blowing Y-Sustain board

        Thanks much for the reply and pictures. I have gone through and measured all of those low value resistors and checked them a couple times. I don't remember if I previously mentioned this, but the 1st time through, I found open resistors in that group of 3 in the upper left corner of that 1st picture. One was at 22 ohms and the other 2 were wide open. I'm guessing something blew them out but that's the only obvious problem I could find. The diode in parallel with them measures good and so does the fuse. And BTW that Sus_Dn section of the Y_Sustain board gets warm in a short time even with the Z Sustain board unplugged from it. With the Z board unplugged I get really dim ghost like unintelligible images so it's at least somewhat working. And the Z bias test points read a perfect 95V, didn't even have to adjust it. The reason I'm suspecting the Z board is because I was reading online that a bad one can cause image to be slow to update. If I go into the menu and then back to the TV station, I can still see the menu on the screen for over a minute before it completely fades out. Also if I change channels, the writing and header from the previous channel will be visible for awhile. I don't have much experience with plasma TV's so I'm basing my assumptions on what I read online so please let me know if I'm wrong. I can get a used tested Z board on Ebay for only $27 and free shipping. For that cheap I'm thinking of giving it a try. What do you think? Thanks again.

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          #44
          Re: LG 50PJ350 plasma blowing Y-Sustain board

          First, try running the set without the Z-SUS plugged in, if the TV allows that (some LGs refuse to power on without it) you should see the image with a purple tint and very dim brightness, they screen may show black spots but with a fullscreen static input it will slowly fill out.
          The image I uploaded shows a Z-SUS board not working entirely, like powering up the TV only with Y-SUS and buffers.

          The SUS_DN part is linked to SET_DN trimpot, it generates a important part of the signal, as with SUS_UP/SET_UP, if it is abnormally hot in a short amount of time even on a black screen something is wrong, if SET_UP and SET_DN are incorrectly set, it causes image retention and some pixelation, but seeing your uploaded images there is also green and red pixels blobs on the screen.

          Also you said that in one board you replaced 30F124 IGBTs, are they original parts? Was that board the original Y-SUS that failed first?

          Those 2R2 resistors don't fail without also something else failing, they act as fuses, if you replaced nothing else on the Z-SUS some IGBT must be bad, following their traces on Z-SUS it leads to 2 IGBTs, and I've circled the others in the same heatsink just in case.
          Attached Files
          Last edited by Biruslapio; 08-24-2020, 08:56 AM.

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            #45
            Re: LG 50PJ350 plasma blowing Y-Sustain board

            OK to answer your question, yes the initial failure was on the Y-Sustain board. It had just about every IGBT shorted and I replaced them all with the same part numbers as the originals. After replacing them with original same parts, should there still be a need to adjust the Set_Up and Set_Down, or should they be fairly close? My scope went through a house fire in 06 and got damp and I haven't attempted to power it up since so I don't even know if it works. Also I don't know how to get an all white screen like they say to have in the training manual. Is that necessary or can I adjust those with a regular picture on screen?

            Besides the IGBT's, there were some open smd gate resistors on the bottom side of them. My original board also had a shorted gate driver IC, IC 70 smd on the bottom side too. The Vcc and ground were shorted together on the IC itself and when I missed it the 1st time, all my new parts went off like firecrackers. The spare board which I got free from a friend in the business also had 7 IGBT's shorted, some gate driver resistors open, and a couple of 1W 2.2 ohm resistors open. So both had similar failures and the original was a little worse.

            None of the IGBT's on the Z board are shorted but I guess it's possible they may have blown open. Being MosFets instead of standard transistors, I can't really test them with a meter so replacing them might be the only way to troubleshoot.

            And yes the TV does work with the harness to the Z-Sus board unplugged from the Y-Sus board and the image is as described, and that heat sink still gets hot even with the Z board disconnected. What did you want me to check for with it disconnected?

            And finally the resistors I mentioned that were open are actually on the upper right of your picture, upper left as the board sits when mounted in the TV. They're actually 20 ohms, not 2.2 so 3 in parallel is just under 7 ohms. I wonder if a power surge from the Y-Sustain board blowing took them out? I'm thinking I'd spend over $10 on replacement IGBT's for the Z board and have to wait awhile if they're in China plus the time to install them is why I'm considering the used complete board on EBay for $27 and it's only 1 state away from me so I should have it in days. I've been working on this off and on since late March/early April and this thread goes back 3 pages. I think a lot of what I just told you is posted there and maybe some other relevant information. I know it's not worth half the time and effort I have into it but it was a project while my work was closed for covid and I'm considering it an educational experience so I can have better luck next time someone wants me to fix a plasma. At this point, it's become a challenge to get it working even though it won't be profitable. I really appreciate you taking the time to help me.

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              #46
              Re: LG 50PJ350 plasma blowing Y-Sustain board

              It's been a while since I've repaired LGs Y-SUS too, so I forgot some details, yes the resistors are 3x20 OHMs in parallel, correct, the others are 2.2OHMs and the red ones are 1 OHM.
              No need to adjust SET_UP/DN if the IGBTs are the same, but it doesn't hurt to try, if nothing gets better just put them at their original positions.

              At this point, my last suggestion before buying another Z-SUS would be to desolder all the Y-SUS and Z-SUS heatsinks with the diodes,MOSFETs and IGBTs and test them one by one with a multimeter to see if they are partially leaking, sometimes they fail but still have some kOHMs or greater resistance between source-drain or collector-emitter. A 50W soldering iron is recommended for this, since it's hard to melt the solder on those big pads.

              You can do it with a multimeter in the 6/20/60 MEGAOHMs scale, put the positive probe on the emitter, and the negative on the collector, should the IGBT have no gate charge, would read 1 megaOHM or greater, and if you swap positive/negative, it should be open, same goes for MOSFETs, diodes should read kiloOHMs forward(A>K) and open or way higher resistance when reverse(K>A). They have to be out of the board because otherwise you're measuring the gate drivers and other components resistance.

              Hopefully some forum member that is familiar with this fault may step up and show the solution right away.
              Attached Files
              Last edited by Biruslapio; 08-24-2020, 10:39 AM. Reason: oops

              Comment


                #47
                Re: LG 50PJ350 plasma blowing Y-Sustain board

                One afterthought, I wonder if the Z sustain board not working properly is putting more stress on those IGBT's and it will be relieved and run cooler once I fix it or have a working Z board in place?

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                  #48
                  Re: LG 50PJ350 plasma blowing Y-Sustain board

                  I have recieved LOTS of fake igbt's from China, Italy, and the UK. I bought a $15 transistor tester kit from Ebay, assembled it, and started checking things. The fakes only read as resistors. Check my pics.
                  Attached Files

                  Comment


                    #49
                    Re: LG 50PJ350 plasma blowing Y-Sustain board

                    Thanks for the heads up on fake parts, that's good to know. Have there been any know issues from US sellers? Fortunately for the rebuild of the Y-Sustain boards, I was able to find everything on Ebay from US sellers. I needed some FDPF51N25's, a 2SK3667 (that one was expensive, $10 for one), some GT30F124's, and RJP63F3A's. Other than the 2SK3667, the rest were around $10 for a 5 or 6 pack of them. I'm assuming the TV wouldn't come on at all if I had bad ones in the Y-sustain board.
                    With this covid thing going on and import restrictions and delays, I'm guessing it would take forever and a day to get anything from China these days so I'm trying to stick to US sellers even if it means paying a little more.

                    The Y-sustain board has 4 GT30F124's and the current best price from a US seller is $12.21 (free shipping) and that's almost 1/2 the cost of the replacement board. I am going to take the suggestion above and desolder all 4 from just the Z sustain board and make sure none are open or leaky. Just about everything was replaced in both Y-Sustain boards and I'm having the same symptom with both so I don't suspect any problems there being all new parts. (7 on one board 8 on the other)

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                      #50
                      Re: LG 50PJ350 plasma blowing Y-Sustain board

                      I pulled all 5 30F124's out of the Z-Sustain board. I'm getting about 1.4 meg between the emitter and collector with the positive lead on the collector on all 5 but nothing in the diode scale between any combination of pins in any direction. Is this normal, and is there any way I can tell for sure if they're good or bad? Not sure if I should order replacements or just put them back in?
                      Last edited by Keshenatech1; 08-24-2020, 03:40 PM.

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                        #51
                        Re: LG 50PJ350 plasma blowing Y-Sustain board

                        That looks good, but the resistance you're measuring is positive on the emitter, and negative on collector (middle pin), there's no other way a GCE IGBT can measure like that, compare those 1.4M OHM to the new ones you bought, they can't be far appart. Of course, use the same multimeter on the same scale.
                        Last edited by Biruslapio; 08-24-2020, 04:55 PM.

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                          #52
                          Re: LG 50PJ350 plasma blowing Y-Sustain board

                          Unfortunately all the new ones I bought are currently installed in the Y-Sustain boards. And assuming both boards are working now, I really don't want to dismantle them. I'm also looking at my scope in case it comes down to adjusting those set-up and set-down adjustments. It's an older one, only 60mhz. Will that be sufficient to accurately measure the waveform at the test point above the top IC on the lower buffer board? There's some minor rust and corrosion on the metal parts but the circuitry looks to be in good shape. I took the outer shell off of it to check it out, and blew out all the dust and cobwebs outside with my new leaf blower. And I sprayed some contact cleaner inside all the switches and potentiometers and worked them back and forth. It hasn't been turned on in about 14 years after getting damp in the basement after the fire but I'm about to power it up. It's a BBC model 6003 I picked up used when I was living in my first house from 94 to 2001 so it's been around awhile. I just powered it up. Power light and back light for the screen scale but unfortunately the CRT doesn't seem to be displaying anything. Edit: After messing around with the controls, I do have a line going across and I can adjust the sweep from low to high speed. Brightness control is a little intermittent but it basically seems to be working, and no smoke or pops so far. It's going better than I thought. Hopefully it's fast enough to measure that signal.
                          Last edited by Keshenatech1; 08-24-2020, 05:41 PM.

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                            #53
                            Re: LG 50PJ350 plasma blowing Y-Sustain board

                            That is exactly why it's needed to compare the IGBTs, if the ones you bought are not equivalent to a 30F124, an incorrect signal will be generated by the Y-SUS, weren't all the 30F124s on the SUS_DN heatsink of both boards replaced?

                            You can use the scope on the Z-SUS board to see if it's working properly, there's a metal jumper called ZSUS_OUT, you attach the scope there, on the buffers at every panel output IC some points are provided, they are pads filled with solder that extend out of the traces that go to the panel.

                            I don't think it's needed to use an oscilloscope on this TV, but I'll send this too, it's a really detailed training manual for a LG 50PQ30 plasma, which is different, so don't take it literally, I've only highlighted the waveform measuring part, the rest is not related to this TV, measuring the full Y-buffer signal requires a 800V pk/pk oscilloscope 100V/div, most have only 400V pk/pk 50V/div with 10x probes.
                            Attached Files

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                              #54
                              Re: LG 50PJ350 plasma blowing Y-Sustain board

                              Yes exact 30F124's were used and both were replaced in the Sus_Dn section of both boards. Having the same image problem with both boards and also with a 2nd set of buffer boards, I was almost positive my problem was on the Z_Sustain board by process of elimination. So I ordered that spare Z-Sustain board on Ebay Monday night and got it already today. Unfortunately it didn't fix the problem so I'm starting to wonder if I have a bad panel. Unless I could have the exact same fault on both Y_Sustain boards? I wish I had another working TV to test them in. The Z board was only $27 and worth a chance but a new/used/refurbished Y board is over $100 and that TV's not worth it. I already have over $100 in IGBT's between both boards plus the Z board I just bought. If I knew for sure my boards were good and the panel bad, I could try to sell the 2 complete sets on Ebay to recover my investment and maybe even make a little profit.

                              One thing I did on both Y_Sustain boards is replaced U704, the 8 pin gate driver for the 30F124's. Vcc to Ground was shorted (on the chip itself) on my original board and it looked discolored on the other board. Even though it didn't measure shorted, I figured it was likely to have been damaged by the 50F124's shorting. The fact that some gate driver resistors were blown open tells me it saw a considerable current surge. From the numbers on the old ones, best I could tell it's a IRS21850 S21850 SOP-8 so that's what I ordered. Hopefully that's the right part for the board. Can anyone confirm? The incorrect spec gate driver could easily cause my image and overheating problem, but it must be at least close for the board to work and not self-destruct immediately. And even if it is the right IC, would it have a different enough tolerance to require major adjustment of the Set_Up and Set_Dn pots? Going to try to look at the wave form tomorrow as it's already past bed time tonight. My scope goes up to 20V/Div and I do have X10 switches on my probes so it should be able to handle it because that would be 200V/div and the recommended setting is 100V/div. And it goes as fast as .05us/div and the waveform adjustment is 180us so there shouldn't be a problem there either. I have the training manual for my model with a good diagram of the wave form and how to set it. I'm hoping I can figure out how to get into the "White Wash" mode. Is that in a special service menu, and do I need one of those special "factory" remotes to get into it? Maybe I'll luck out and just have the problem to be those adjustments. Instead of trying to hold the sharp point of my probe on that delicate test point on the lower buffer board, I'm going to carefully solder a little clip lead on that point to clip onto. Going to attempt all this tomorrow night after work so any input or suggestions would be appreciated. Thanks again.
                              Attached Files

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                                #55
                                Re: LG 50PJ350 plasma blowing Y-Sustain board

                                White wash means a full white input on the screen, no power saving options enabled, and also wait 15 minutes for the TV to heat up.
                                The panel is not the problem, the problem is poor sustaining, I bet on the 30F124 IGBTs that were replaced, you much probably have original 30F124s on the Z-SUS that you bought, try to replace the 30F124s in one of the Y-SUS boards.

                                About the IRS21850, if it's the same model that the one replaced, it will work.

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                                  #56
                                  Re: LG 50PJ350 plasma blowing Y-Sustain board

                                  Thanks for the info about entering White Wash mode. Going to check it out when I get home. As for replacing the 50F124's, can you please explain the logic in replacing them on one of the Y-sustain boards again? Do you suspect I got a bad batch of them the first time? Both of them are brand new on both boards. Thanks again

                                  Comment


                                    #57
                                    Re: LG 50PJ350 plasma blowing Y-Sustain board

                                    tvtimmy warned about fake IGBTs, you said you bought "original parts of the same model", but there's no way to know that without measuring and comparing them, I suspect they are fake, swap them with the ones on your spare Z-SUS board which should be original, unless someone replaced them already.

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                                      #58
                                      Re: LG 50PJ350 plasma blowing Y-Sustain board

                                      Check them in diode mode. Check YouTube for igbt testing.
                                      I bought most of my fakes from US sellers. One clown asked if I knew what I was doing, I asked him if he owned a multimeter and to check them for himself . HE said no refunds, I think I told him to GFYS. Ebay took care of me though.
                                      Last edited by tvtimmy; 08-27-2020, 03:55 PM.

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                                        #59
                                        Re: LG 50PJ350 plasma blowing Y-Sustain board

                                        I replaced 30F124's, A 2SK3667, some PFPF51N25's some RJP63F3A's and that IC. How do I know that one of the others isn't bad and not just the 30F124's? The seller for the 30F124 has a 99.9% positive feedback rating with only one negative in 12 months for an entirely different product out of over 1000 transactions. I should check the other sellers' ratings and see if there are any reports of bad/fake parts. If they all look good, I'm going to start with looking at that waveform on the scope before I go through the work of changing that board again. It has like 18 screws, all needed to make connections, and 2 ribbon cables that have the "force in" type connector with no release. They've been in and out so many times already I'm afraid of tearing a trace if I mess with them too much more. If I had fake/bad ones, would I even get a picture at all?

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                                          #60
                                          Re: LG 50PJ350 plasma blowing Y-Sustain board

                                          Missed the part that you also bought some RJP63F3A, I've bought 15 of those on a local shop here and all of them were fake, looked totally different from the original part, exploded my y-sus board 4 times and never even powered up, got refunded though, they are rare to find genuine. The 51N25 is a regular mosfet, as the K3667, never saw someone try to fake those yet.

                                          Usually fake IGBTs work for some short time then fail, can't handle the pulse current, or the VCE breakdown voltage is not up to spec, or they have straight out crap inside them that can't even handle 30V VCE, immediately blowing up.

                                          https://alpengeist-tvrepair.blogspot...ansistors.html < this blog is really good, but not updated anymore.

                                          Chech the board with the oscilloscope and try to adjust set_up/dn anyway, it should not damage anything.

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