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Old 07-15-2019, 06:10 AM   #1
GraphicMan
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Default CRT TV LG RT-29FB75VE faint noise 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?
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File Type: jpg Lines.jpg (99.4 KB, 15 views)

Last edited by GraphicMan; 07-15-2019 at 07:21 AM..
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Old 07-15-2019, 09:43 AM   #2
Andrew F. Ali
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Default Re: CRT TV LG RT-29FB75VE noise faint on screen

There is a capacitor or GND connection loose.
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Old 07-15-2019, 01:41 PM   #3
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Default Re: CRT TV LG RT-29FB75VE noise faint on screen

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Originally Posted by Andrew F. Ali View Post
There is a capacitor or GND connection loose.
in which area in the board plz?
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Old 07-15-2019, 02:55 PM   #4
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Default 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.
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Old 07-15-2019, 03:41 PM   #5
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Default Re: CRT TV LG RT-29FB75VE noise faint on screen

Quote:
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
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Old 07-15-2019, 04:50 PM   #6
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Default 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
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Old 07-15-2019, 05:54 PM   #7
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Default 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

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Old 07-15-2019, 10:02 PM   #8
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Default Re: CRT TV LG RT-29FB75VE noise faint on screen

Quote:
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!!?!!
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Old 07-16-2019, 08:39 AM   #9
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Default 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.
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Old 07-16-2019, 01:34 PM   #10
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Default Re: CRT TV LG RT-29FB75VE noise faint on screen

Quote:
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
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Old 07-16-2019, 03:25 PM   #11
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Default 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.
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Old 07-17-2019, 12:03 AM   #12
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Default Re: CRT TV LG RT-29FB75VE noise faint on screen

Quote:
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
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