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LG42PC3D has sound, very distorted and almost nonexistent picture

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    #1

    LG42PC3D has sound, very distorted and almost nonexistent picture

    This is my first plasma repair attempt. It is (the fairly infamous) LG42PC3D. It does have sound when connected to a source, but has an almost nonexistent picture. What does show up is tinged red, and sometimes seems like red sparklies. Upon turn on, there is a slight bit of white distortion which I couldn't get to show up on video (but is what I think is an LG logo). Upon shut down, the right half (not perfectly half, the division is jagged) of the screen flashes static 3 times and shuts down.

    I have read through the plasma troubleshooting guides posted by Tom and plan to try a few things out when I have some time tomorrow. Until then though, does it sound like the panel is shot?

    Here is a quick video:
    http://s294.photobucket.com/user/wit...tml?sort=3&o=0
    I realize how near worthless that is, and can do better if you need me to. Right now though, I have to run to work.
    Tags: None
    #2
    Re: LG42PC3D has sound, very distorted and almost nonexistent picture

    To me, it looks like a Z-sustain or control board issue. I don't think the panel is shot.
    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.

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      #3
      Re: LG42PC3D has sound, very distorted and almost nonexistent picture

      YSUS and ZSUS each have 2 swap-able fuses and 1 picofuse (that I can find). All test OK. Do ok fuses mean that the boards are ok? After all the reading I've done, especially with this POS model, the fault really seemed to be with the ZSUS.

      I suppose I ought to start taking the back out to get to the control board, huh?
      Last edited by withalligators; 09-12-2013, 08:17 AM.

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        #4
        Re: LG42PC3D has sound, very distorted and almost nonexistent picture

        Ok, I got down to the control board. It's a tiny little thing, isn't it? Is there any testing or anything I can do on it? Do I have to just replace it and see?

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          #5
          Re: LG42PC3D has sound, very distorted and almost nonexistent picture

          Quick bump, and so I can subscribe to replies by email. Is it possible to have a burned out ZSUS board while still having good fuses? If not, should I buy a new control board?
          Thanks!

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            #6
            Re: LG42PC3D has sound, very distorted and almost nonexistent picture

            Usually the Z-sustain fails with blown fuses. Rare for it to fail another way on 42". On 50", the ER-IPM can fail without the SUS-IPM failing, but that does not apply on 42". Capkid may know about these older LGs and test patterns, I don't touch them any more.
            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

              #7
              Re: LG42PC3D has sound, very distorted and almost nonexistent picture

              I agree with much of what Tom has stated: It appears to be either a failing Z-Sus or control board. I don't know of any control board tests for this TV. Here's what I'd do:

              (1) The standard voltage confirmation - there should be test points. If you're unsure about how to check, I can diagram this for you when I get home tonight:
              Power supply: VS and VA
              Y-Sus: -Vy and VSC
              Z-Sus: Vzb (aka Zbias)

              (2) If you have access to an oscilloscope, you can check waveforms.

              (3) If the above tests show no abnormalities, I'd replace the control board. The Vzb voltage check might tell you right away if your Z-Sus is failing.

              Edit: This is a 42V7 test pattern video: http://www.youtube.com/watch?v=soZ9jblKBpE

              I'm not sure how different the 42V7 control board is from yours (I believe yours is 42X3).
              Last edited by capkid; 10-29-2013, 02:54 PM.
              LG Plasma Mal-Discharge Correction Service

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                #8
                Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                Power supply is outputting VS @ 184V and VA @ 60V, which is what's labelled.
                -VY @ 200V-201V or negative 200V-201V depending on the test prong, and VSC @ 120V +/- 1V
                VZB @ 100V.

                So everything is right where it should be, it seems. I guess I should adjust the VY and VSC and order up a control board?

                Thanks!
                Alex

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                  #9
                  Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                  There are no guarantees replacing the control board will correct your issue. Using an oscilloscope to check waveforms would probably give you a more definitive answer. However, if you don't have access to an oscilloscope, I'd just replace the control board and see what happens.
                  Last edited by capkid; 10-30-2013, 11:44 AM.
                  LG Plasma Mal-Discharge Correction Service

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                    #10
                    Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                    I don't have one nor know how to use one. I see there is an app to simulate one though, which would be interesting. Everything I've read makes this look like a ZSUS failure, but the fuse isn't blown and the voltage seems ok.

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                      #11
                      Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                      ok. I'd try replacing the control board first, since it's usually the cheaper of the two.
                      LG Plasma Mal-Discharge Correction Service

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                        #12
                        Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                        Well, as expected, the control board didn't do it. It's only ten bucks down the drain though. I was going to give this to my gf's mom, but she got a little samsung 32" that she's happy with. So now I have to figure out if this thing is worth the cost of a zsus board. It seems they can be had on ebay for 40 to about 100.

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                          #13
                          Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                          Unfortunately, there's nothing conclusive that says a replacement Z-Sus will correct the issue, either.
                          LG Plasma Mal-Discharge Correction Service

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                            #14
                            Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                            I've repaired at least 7 of these LG plasmas from various issues. If you have sound, I agree with Tom66 that the Z-sustain is likely the problem.

                            Common problems I have found on this type of LG are:

                            1) bad 3300uF/10V capacitors on the power supply board secondary...
                            2) bad y-sustain
                            3) bad z-sustain
                            4) bad y-buffer (usually black horizontal lines)

                            1) Bad power supply capacitors result in a TV that would click repeatedly when trying to turn on, or the TV would take forever to turn on. This is the cheapest repair and somewhat easy to diagnose (from bulged caps)

                            2) Bad Z-sustain usually resulted in having audio, but no video. (This is like your problem) I think the screen would appear to have a raster (lit up) in dark room, but no image. Sometimes the red or green sparklies would appear in areas that were prone to burn in. I think most times one white ceramic fuse or the other on this board would be burned.

                            3) Bad y-sustain would usually manifest as one of two problems...

                            A) prevent TV from turning on at all.
                            B) You get audio, but no video (also similar to your problem).

                            I've also read that missing 15V on the Y-sustain could be a problem, but have never had that issue personally.

                            I've never had to replace the logic control board.

                            I had a spare TV with good boards and bad panel (horizontal lines), so I was always able to troubleshoot the boards and do a swap to confirm...

                            My guessis the Z-sustain board, but I would check all voltages on the Y-sustain.

                            Otherwise, with the TV unplugged, disassembled, and discharged, I would take ohm-readings on the bottoms of the Z-sustain and Y-sustain boards from Va-to-gnd, VS-to-gnd, 15V-to-gnd, etc right below the IPM modules... The pins are clearly labelled on the circuit board. low resistance to ground from any of those pins is bad.

                            Additional advice: There is no active cooling in these TVs above the heat sinks on the Z-sustain or Y-sustain. They run very hot. On each unit I repaired, I creatively mounted cooling fans (spliced into 9V wire on power supply) to blow air on the heat sinks. Once they are kept cool, they are just about the most reliable TV I have ever worked on.
                            Last edited by Unspun01; 11-04-2013, 04:18 PM.

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                              #15
                              Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                              Thanks guys, ZSUS did it. I wish the resolution on this was higher, I'd be tempted to keep it myself with the proposed cooling fan mounting. Do you just use old PC cooling fans? I have about 8 quadrillion of those laying around if so. Any chance of a pic to get an idea of what you did?
                              Thanks again,
                              Alex

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                                #16
                                Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                                Cool!
                                LG Plasma Mal-Discharge Correction Service

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                                  #17
                                  Re: LG42PC3D has sound, very distorted and almost nonexistent picture

                                  I'd like to attempt the aforementioned PC fan mounting. I'm fine with simply JB welding the fans onto the heatsink facing towards it. I am unclear about how I would splice the wires into the pre-existing system. Any pointers? I don't see a pin marked 9V on any of the plugs.

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