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Vizio P42HDTV10A Flickering Screen

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    #1

    Vizio P42HDTV10A Flickering Screen

    Hello, like many I see on here I have an LG Plasma with screen issues but no issues with sound. I have a decent background in electronics but zero experience in tv repair. So I've spent several hours reading posts, getting familiar with the components, and testing. I'm still poking around but I'd like some direction from the experts.


    Here are the part numbers for this set.
    Vizio model: P42HDTV10A
    LG Model: PDP42X32000
    6871QZH056B
    6871QYH048B
    6871QDH117A
    6871QCH077C
    6871QRH068A
    6871QLH059A

    Symptoms:
    Screen is mostly white noise with the entire screen flicking off and on at a high rate. You can see the on-screen display but it's very faint and distorted. Connecting a single results in some picture but it's highly distorted and very faint. Mostly black with image outlines in bits of color.


    I've done the basics:
    -Tested all removable and surface mount fuses. no issues.
    -Tested the output voltages on the power supply. no issues.
    -Removed all the boards, inspected the traces and caps.
    No obvious cap issues. I did notice odd something on the zsus board. There is a sticky substance like grease covering about a quarter of bottom. No obvious source.
    -Some post mentioned running the set for 10 minutes and finding "cool" boards. Well I tried that and everything was cool I used a thermal gun while running and touched everything once off. I wasn't running a single so maybe that was the issue.
    -The ysus board 'ticks' at a high rate when the set it on. I wasn't sure if that was normal. It's possible it's ticking in time with the screen flicker but my eyes and ears can't agree today.

    One of the other posts mentioned "Troubleshooting Manual 2007 VG training plasma". This was really useful but I could not do some of the tests because the p50 it's based on is too different. I couldn't find the test points it mentioned to scope. Is the a training manual for this model? I wanted to test the bias of the hybrid circuit but need to procedure. Based on what I've read I think it's the zsus that's the problem but I'm guessing.

    Can someone suggest some next steps?

    Thanks,

    -Bill
    Last edited by bill_; 02-25-2012, 05:49 PM.
    Tags: None
    #2
    Re: Vizio P42HDTV10A Flickering Screen

    I had the 50" version of this tv. The picture on mine was flashing very similar to yours, with a coresponding "ticking" noise coming from the Ysus board.

    I sent my board to Coppel's tv repair in the DFW area to have the IPM/Hybrid replaced. That fixed the tv.

    Comment

      #3
      Re: Vizio P42HDTV10A Flickering Screen

      Thanks, that was my thought when I heard the ysus ticking but I wanted to be sure. I did some more digging and found some testing procedures for the IPM here:

      and here:
      http://monitor.net.ru/forum/files/ip...boards_456.pdf

      and here:
      http://blog.coppelltvrepair.com/2011...s-ipm-for.html

      The forward on (GND)-(SUS-OUT) and (SUS-OUT)-(VS) is 0.378. The reverse on (SUS-OUT)-(VS) is 0L which I believe is infinity on my meter. This is for both the ZSUS and YSUS.

      I also tried the short tests on Coppell's site and they check out too. All my tests were in circuit which is not supposed to matter. I realize these tests are not 100% but I feel like I'm missing something.

      Somewhere I saw a manual that covered a bunch of scope measurements but I lost the link. It wasn't for the same set but from what I've read all of these plasmas work the same so I thought I'd give it a shot.

      Comment

        #4
        Re: Vizio P42HDTV10A Flickering Screen

        You want the LG Plasma Quick Reference Alignment Handbook. It's available at Elektrotanya.

        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

          #5
          Re: Vizio P42HDTV10A Flickering Screen

          Thanks PlainBill this was exactly what I was looking for and I believe you posted the LG TV Plasma Training Manual in another thread which was very helpful for understanding the big picture.

          I took some measurements and now I'm thinking I have a power issue on the ysus and not a ipm issue.

          Here is what I found
          Code:
          panel (measured)
Va  60  (60.0)
Vs  184  (184.7)
Vsc 120  (120)
Vy  -200 (242-260 unstable)
Vzb 100  (100)
5v     (5.09)
          It appears the Vy is the problem and the block diagram in the training manual shows this voltage is independent from the ipm. I've done some short circuit and cap testing in-circuit and didn't find anything. This was all on the main ysus board and not the VSC Adj and -VY Adj risers.

          Is it time to start pulling off components? Or is there something I should look at first? I was thinking about puling off the -VY Adj board but I wasn't sure how common it was for that to break.

          Thanks,

          -Bill

          Comment

            #6
            Re: Vizio P42HDTV10A Flickering Screen

            just fixed a vizio p42hd10a that was flickering, quick inspection found the usual power board cap problem. well that blew a couple of hrs later. retraced steps and looked for other faults,when i found the problem it was the inverter board caps swollen. i removed the cover to check the esr and saw them swelled, just for fun thought i would check the esr anyway, .03 put a few volts thru them and they went off scale.possibly they go high esr before swelling. mine now has 1000uf@50volts versus 470uf@35,now to see how long they hold up

            Comment

              #7
              Re: Vizio P42HDTV10A Flickering Screen

              @awyatt2
              I scoped my power supply and the Va and Vs looked clean so I doubt that is the problem.

              I didn't have much time this past weekend but I did manage to trace out the supply to the -VY Adj. Both the -VY Adjust and VSC Adjust are feed by Vs. I attempted to remove the board but apparently my desoldering skills suck. The best I could do was turn the solder to a soft putty which was not good enough to suck it off. Even with my iron at its hottest, 900F, I was only burning the PCB. I've heard some people mention using chipquik to lower the melting point. Maybe I'll try that.

              Another option is to remove the ysus and power it on the bench so I can trace the contacts on the bottom. I'm pretty sure the power is clean feeding the VY Adj but I can't measure it because it's on the underside. Since the Vsc is clean and both boards have the same source I don't think that's the issue. I'm thinking either the Adj board is bad or something the board is feeding is shorting out which is causing the erratic swings in the output.

              Well, I have the rest of the week to think about it.
              Last edited by bill_; 03-07-2012, 09:40 PM.

              Comment

                #8
                Re: Vizio P42HDTV10A Flickering Screen

                I finally was able to remove the VY Adjust and VSC Adjust boards. I went ahead and removed both so I could compare them. I found the key to desoldering the boards was a larger tip, 800F and flux. The two pins that go through the large copper plane are still problematic.

                I couldn't find an cap issues. I even removed c20,c25 just incase something was throwing off the in-circuit reading. I was getting an off reading from the FET (Q20). It wasn't shorted but differed from the VSC board. I removed it so I could better test it but fired it in the process. The FET is a Fairchild FQPF8N60C. Can someone recommend a supplier? Digi-key does't stock it. Mouser does but shipping is $12 for a $1.50 part seriously?

                As always, hindsight is 20/20. I really should have removed the VY resistor first so I could measure the VY without anything interfering later in the circuit.

                I read this thread
                https://www.badcaps.net/forum/showthread.php?t=16274
                but the board design differs. Mine has these markings:
                PDP DOC 128B
                REV 1.1

                Transformer is:
                0047X-F
                DK 60212C

                The only active components are:
                FQPF8N60C
                200D6 PAIC I see this is a PWM but I'm not sure if I have the correct data sheet.

                Any suggestions before I order parts? Anything else I could test? I thought about powering the board but my supply is only 5v. I could also do some testing with the ysus back in the set without these boards. I could run 185v from the set into the board but I'm reluctant. It's so small I'd need something non-conductive and stable to hold it. Also the smd on it are so tight I'm worried about shorting something.

                -Bill

                Comment

                  #9
                  Re: Vizio P42HDTV10A Flickering Screen

                  It's been a while and I'm finally getting back to this project.

                  The adjust boards tested fine out of circuit so I replaced them. Next I removed the Top Y-Driver board and the VY issue disappeared. A nice stable 200v. The driver board is mostly ICs and the few caps it has look normal.

                  Should I replace this board? or is there some more digging I can do?

                  Thanks,

                  -Bill

                  Comment

                    #10
                    Re: Vizio P42HDTV10A Flickering Screen

                    I just got my ysus back from coppel tv. Looks like they replaced two of the large transistors where the buffer connects. I now have picture but there is a faint rgb noise covering the entire picture.

                    Any ideas?

                    -Bill

                    Comment

                      #11
                      Re: Vizio P42HDTV10A Flickering Screen

                      I have similar problem, I replaced the big moduler in the Y board. After replaced it seems fixed my previous problem-" no video, has sound". The image is shiown afterward. But the screen image become dimmer and "snow" dot. Is any test point that I can test out the Y board is in good voltage level, all I want is make the image back to normal.

                      Comment

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