Announcement

Collapse
No announcement yet.

CRT TV LG RT-29FB75VE noise faint on screen

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    CRT TV LG RT-29FB75VE noise faint on screen

    Hello guys
    Tv picture is in almost perfect condition
    but out of nowhere i noticed a really very faint wavy noise overlay on the screen like the attached graphic picture I attached
    I am sure I never saw this before
    it appear on any video connection, so it has nothing to do with the jacks I believe
    it is almost invisible on whites and blacks
    , it is really faint, the screen has to be static to start noticing it, it also kinda moving from down to up

    what could that be?
    Attached Files
    Last edited by GraphicMan; 07-15-2019, 07:21 AM.

    #2
    Re: CRT TV LG RT-29FB75VE noise faint on screen

    There is a capacitor or GND connection loose.

    Comment


      #3
      Re: CRT TV LG RT-29FB75VE noise faint on screen

      Originally posted by Andrew F. Ali View Post
      There is a capacitor or GND connection loose.
      in which area in the board plz?

      Comment


        #4
        Re: CRT TV LG RT-29FB75VE noise faint on screen

        This looks like a bad cap on one of the low voltage supplies, either in the main power supply or the voltages supplied by the flyback.
        C419,C415,C413 or C822 or others
        This is high frequency noise (rilpple) getting into the video signal somwhere, easy to find with a scope.

        Comment


          #5
          Re: CRT TV LG RT-29FB75VE noise faint on screen

          Originally posted by R_J View Post
          This looks like a bad cap on one of the low voltage supplies, either in the main power supply or the voltages supplied by the flyback.
          C419,C415,C413 or C822 or others
          This is high frequency noise (rilpple) getting into the video signal somwhere, easy to find with a scope.
          very informative, thanks a lot
          you know i have already replaced the original str but with a lower watt version!
          but the tv is working fine for many months so far, also i am placing a 10cm fan infront of the fbt and the heatsink with have the str, it helped to drop the temp of the heatsink from 71 to 41 max! )already placed a sensor on the heatsink

          so could that be from the str? it is not original and not the same model also W6756 instead of the original X6756

          fbt also replaced with a chinese one not the same model

          Comment


            #6
            Re: CRT TV LG RT-29FB75VE noise faint on screen

            I can't see the str causing that type of problem, (or the flyback for that matter) the main power supply runs at a high frequency similar to the horizontal circuit, so if the secondary supplies are not filtered properly that ripple can enter other circuits and when it does it can look like your picture.
            Poor filtering on any of those 78xx or S1117 regulators can also cause this problem. when the regulators are not filtered properly they can oscillate on there own causing this type of interference

            Comment


              #7
              Re: CRT TV LG RT-29FB75VE noise faint on screen

              the screen is telling you something . its acting like a scope .. i remember that pattern but no idea what causes it . might be huntron tracker i remembered . sorry bit gone on tonight .
              octopus
              Last edited by petehall347; 07-15-2019, 05:57 PM.

              Comment


                #8
                Re: CRT TV LG RT-29FB75VE noise faint on screen

                Originally posted by R_J View Post
                I can't see the str causing that type of problem, (or the flyback for that matter) the main power supply runs at a high frequency similar to the horizontal circuit, so if the secondary supplies are not filtered properly that ripple can enter other circuits and when it does it can look like your picture.
                Poor filtering on any of those 78xx or S1117 regulators can also cause this problem. when the regulators are not filtered properly they can oscillate on there own causing this type of interference
                that is very valuble information for me
                but you have said earlier that it could be from the low voltage power supply, and the str is the low voltage ps, right?!
                if u look in its manual, the str provide many low voltage outputs for this model, i am just wondering if it is failing
                btw i have another interesting question
                I am sure i have adjusted the tilting of the screen from the main menu
                but then when i moved the tv from place to another in same room (very carefully) I noticed that the screen is noticeably tilted!! and when i went to adjust it i found that it is on the same setting unchanged and when i tried to readjust it i found that i am out of adjusting range, the screen is barely leveled at the very far end of the range possible to adjust, how is that possible!!?!!

                Comment


                  #9
                  Re: CRT TV LG RT-29FB75VE noise faint on screen

                  When I said low voltage supplies I ment the 5 volt or the +/- 14v.
                  The tilt of the screen can be effected by a weak magnetic field. even the earth's magnetic field can effect it. A metal pipe in the wall or metal beam would have this effect on the monitor.
                  If you have a small magnet (or if your screwdriver tip is magnetic), move it around the back of the tv near the neck of the crt and you will see its effect.

                  Comment


                    #10
                    Re: CRT TV LG RT-29FB75VE noise faint on screen

                    Originally posted by R_J View Post
                    When I said low voltage supplies I ment the 5 volt or the +/- 14v.
                    The tilt of the screen can be effected by a weak magnetic field. even the earth's magnetic field can effect it. A metal pipe in the wall or metal beam would have this effect on the monitor.
                    If you have a small magnet (or if your screwdriver tip is magnetic), move it around the back of the tv near the neck of the crt and you will see its effect.
                    got you
                    what about vertical lines not being straight similar to the attached pic
                    and what to do about it?
                    thanks
                    Attached Files

                    Comment


                      #11
                      Re: CRT TV LG RT-29FB75VE noise faint on screen

                      I buy a new monitor.
                      The sides (vertical) should be straight, The vertical scan is a saw tooth wave and will be linear . something is modulating the vertical scan and causing the bumps you see. Again it could be poor filtering somwhere.

                      Comment


                        #12
                        Re: CRT TV LG RT-29FB75VE noise faint on screen

                        Originally posted by R_J View Post
                        I buy a new monitor.
                        The sides (vertical) should be straight, The vertical scan is a saw tooth wave and will be linear . something is modulating the vertical scan and causing the bumps you see. Again it could be poor filtering somwhere.
                        yes exactly like u said bumps, it is much less sever than the attached picture, but I want you to get the idea, I think I should replace all caps, I am also sure I was not seeing this defect before
                        thank RJ

                        Comment

                        Working...
                        X