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Vizio VS420LF1A - Attack of The Black Screen

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    #1

    Vizio VS420LF1A - Attack of The Black Screen

    Hello,

    I have searched everywhere throughout these forums and on the web, and I've read just about every possible scenario of problems with LCD TV's except mine. The closest post that I found was posted by RRR13 about one year ago. Who had a similar issue - read here. So I thought I would get my story out there in hopes that I may be able to help another fellow poor sap with the same exact problem as me.

    Here's my initial observations: Black/grey screen when powered on for all inputs and menu screens, but I DO hear audio for all inputs. Vizio logo is orange when off, white when on. Backlight does work like champ.

    Observations when I opened it up: I saw no bad capacitors or any visual signs of blown fuses. (FYI-I do not own voltage/wattage testing equipment). I proceeded to plug in power. The T-conn board had a blue LED light that came on along with the backlight when I first turned the TV on. Several seconds after the white backlight came on, the blue LED light faded out to black. I became aware of a very faint hum after about a 30sec. - I believe it's coming from the power board, didn't wanna get my ear too close while the power was on.

    My uneducated guess is that the T-Conn board needs to be swapped. I'm trying to think of any other observations. What do you guys think? What else would you like to know?

    One other weird thing is that when this all began there were times when the screen did come back to original working perfection when I had the TV unplugged for a while, and then powered it up. The problem is that those moments got fewer and further between as time progressed. I remember the first time I noticed, it was about a week ago. The screen went black and I thought it was the hdmi input. The remote was actually able to change the input and I could then hear the sound from the tv input but the screen was still dark grey. The TV then came back to life and worked without a hitch until about two days ago.

    The blackness came again and it was harder to shake that time. I turned the power off, unplugged tv, and held power button down (don't believe this model has a reset but tried anyway) the tv came back on and worked perfect for about 3 hours and repeated the dreadful process. It is now to the point to where the blackness rules, and my movies drool.

    Any help is much appreicated! Thanks.

    Travis
    Tags: None
    #2
    Re: Vizio VS420LF1A - Attack of The Black Screen

    Here are some pictures. Let me know if you need a close up or a different angle. Also update: Just started noticing a different sound (like a stuck pig - well, the sound a stuck pig would make if it was the size of an ant) coming from the control board.
    Attached Files

    Comment

      #3
      Re: Vizio VS420LF1A - Attack of The Black Screen

      Originally posted by travisristick View Post
      Here are some pictures. Let me know if you need a close up or a different angle. Also update: Just started noticing a different sound (like a stuck pig - well, the sound a stuck pig would make if it was the size of an ant) coming from the control board.
      One point - terminology is important if we are to communicate. 'Control board' is ambiguous. There is the Tcon (Timing control board), the board with the buttons (control panel), and the main board which controls everything. There is some justification for calling any of these the 'control board'. Henceforth we shall speak of the power supply, the main board, the tcon, and the control panel.

      Intermittent failures like this are often caused by a bad solder joint. This could be on either the main board or the tcon. And as you might suspect, they are a bear to locate. One method is to use something like a 'stick' pen to tap and prod various points in hopes that something will stop or start working.

      If you want something easier to start, I identify 7 voltage regulators on the main board. They are U2, U4, U5, U8, U9, U11, and one below U11 whose identifier is washed out by glare. The best way to do this is to record the identifier (U2), the part number (may be something like NCP1117ST33T), and the voltage on each of the three pins (numbering for U2 is left to right, the tab and the center pin are connected together). Use the mounting screw in the middle of the board as the ground point.

      Of course, if you can get readings both working and not working, it would be a big help.

      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

        #4
        Re: Vizio VS420LF1A - Attack of The Black Screen

        PlainBill,
        Thanks for your response. Yes, my terminology is very inconsistent - I hope you were able to decipher what I was saying for the most part - From what you have written it sounds like you have. I'll attempt to test tonight. Please stay tuned. Thanks again.

        Travis
        Last edited by travisristick; 06-30-2011, 06:13 PM. Reason: gathered new information regarding my availability

        Comment

          #5
          Re: Vizio VS420LF1A - Attack of The Black Screen

          Here is the types of voltage regulators for now:

          U2, U4, U5, U7, U8 - K481 G1117
          U9 - 1084 0845CL
          U11 - 7805CT RAF842G
          Last edited by travisristick; 06-30-2011, 06:14 PM.

          Comment

            #6
            Re: Vizio VS420LF1A - Attack of The Black Screen

            Generally speaking, a white, gray, or black screen (as in backlights working, but screen shows no picture) would usually indicate a bad T-con. However, since you said the sound is also not present, I am more inclined to think it's PSU or the main board and not the T-con. The PSU seems to use good brand capacitors, though.

            U11 is a common 7805 voltage regulator - it should have 5v on it's output pin when a voltage higher than about 7v on its input is present.
            U2, U4, U5, U7, and U8 - I'm not sure if they are BUK481 MOSFETs or 1.7v regulators. Might be the latter, but I'll wait for PlainBill (or someone else) to confirm.
            U9 I'm can't find.

            Comment

              #7
              Re: Vizio VS420LF1A - Attack of The Black Screen

              Originally posted by momaka View Post
              Generally speaking, a white, gray, or black screen (as in backlights working, but screen shows no picture) would usually indicate a bad T-con. However, since you said the sound is also not present, I am more inclined to think it's PSU or the main board and not the T-con. The PSU seems to use good brand capacitors, though.

              U11 is a common 7805 voltage regulator - it should have 5v on it's output pin when a voltage higher than about 7v on its input is present.
              U2, U4, U5, U7, and U8 - I'm not sure if they are BUK481 MOSFETs or 1.7v regulators. Might be the latter, but I'll wait for PlainBill (or someone else) to confirm.
              U9 I'm can't find.
              You are right, U11 is a common 7805.

              Voltage measurements will verify this, but the 1117's are .8A or 1.0A regulators. Google 1117 regulator for more information. If they were mosfets the identifier would start with Q, not U. These appear to be the adjustable version.

              The 1084 is a higher current (5A) version of the 1117. Google 1084 regulator for more information than you ever wanted to know.

              These are pretty standard. Expect to see 3.3, 2.5, 1.8 and sometimes 1.25 volt regulators.

              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

                #8
                Re: Vizio VS420LF1A - Attack of The Black Screen

                After taking false measurements for about 10 minutes (multimeter issues), with the screen on the floor, the screen turned from blackness to blue glow without me knowing. When I finally figured out the top voltage setting (there were two) was the one I needed to be on, I started getting the following measurements.

                Voltage Measurements with TV on (fully working and with me unaware)

                U2 - Input: 4.8 Output: 3.2 Pin3: 2.01
                U4 - Input: 4.5 Output: 3.29 Pin3: 2.05
                U5 - Input: 4.8 Output: 2.62 Pin3: 1.37
                U7 - Input: 4.8 Output:2.03 Pin3: 2.8
                U8 - Input: 2.5 Output: 1.24 Pin3: 0
                U9 - Input: 4.8 Output: 2.5 Pin3: 1.25
                U11 - Input: 2.66 Output: .66 Pin3: 0

                When I first checked U8 I was like aha! I triple checked U8 and U11 at the very end because they were the odd one's out. I finally went to lift up the tv and look at the screen for the heck of it. I went from aha, to what the #*$%.
                It's been on and running ever since. I guess we'll see what happens. So it may just have been a bad solder joint as PlainBill predicted. I'm not quite celebrating, but it's a step in the right direction. I really thought the measurements for U11 and U8 were odd. Odd in the sense that I thought I'd see numbers like that with the TV black, not perfectly functional. What do you guys think?

                Oh, to clarify any misunderstanding from my original post. Sound has worked the whole time, the only thing that was the issue was the infamous 'Black Screen' .

                Comment

                  #9
                  Re: Vizio VS420LF1A - Attack of The Black Screen

                  As Arte Johnson used to say 'Verrry Interesting'.

                  I see an anomaly, and one point I question.

                  The adjustable versions of the 1117 and 1084 families of regulators uses a 1.25 volt reference; the output voltage is always 1.25 volts higher than pin 1 (the Adj pin). U7 represents an anomaly. The output voltage is too low. Also, U11 is not getting the proper input voltage. I have no idea why, other than to assume those regulators are not used for this particular input. And I have no idea why the TV is working.

                  It IS time to probe for bad solder joints.

                  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

                    #10
                    Re: Vizio VS420LF1A - Attack of The Black Screen

                    Originally posted by PlainBill View Post

                    As Arte Johnson used to say 'Verrry Interesting'.

                    PlainBill
                    Who dat be ? ? ?
                    The strong-minded rise to the challenge of their goals,the weak-minded BECOME HATERS

                    Comment

                      #11
                      Re: Vizio VS420LF1A - Attack of The Black Screen

                      Originally posted by Dgtech View Post
                      Who dat be ? ? ?
                      The are kids Bill.

                      Comment

                        #12
                        Re: Vizio VS420LF1A - Attack of The Black Screen

                        Originally posted by Dgtech View Post
                        Who dat be ? ? ?
                        http://webcache.googleusercontent.co...www.google.com
                        Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                        Comment

                          #13
                          Re: Vizio VS420LF1A - Attack of The Black Screen

                          Originally posted by Village Electronics View Post
                          The are kids Bill.
                          Being young is nothing to be ashamed of. An inability to use Google....???

                          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

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