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Help with Interference on RGB osd mux Lg 20” cp-20b85


m.andrade1

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Hello Guys

With the help of a very good friend Mark from Australia, i was able to mod a Lg 20” cp-20b85 Rgb osd mux the chassi is MC-83a, the process was perfect except with a noise with a "S" dancing pattern that is occuring specialy with solid background, below is the album with the instalation and examples with that interference.

 

Will try to describe the walkthru that Mark and i did on this chassi:

a) This mod was intend to run with a pc with an ATI-5450 (patched with 15khz) and CRt_Emudriver 2.0 beta 10 on windows 7

b) took of the RF modulator to avoid any future interference, and on that spot solder GNG (pin 10) from vga

c) Used the 5v from RF to feed R50 to trigger the FB

d) Sync did the twist on pins 13 and 14 with 1k in each them twisted togheter and run it on AV central pin

e) bring colours from VGA direct in a 75ohms already exist spot in chassi near rgb resistor (220ohs) on chassi.

 

To try to show Mark the interference with a very good way not only as a "ghost" on background i put a pot 10k on 5v source, and when you turn it almost to make trigger disappear or oposite almost to trriger on, the real "S" dancing interference pattern show all in it´s glory.

 

Album with instalation: https://photos.app.goo.gl/Qkxyc2ptez2guZxH7

 

So if anyone have some idea or a clue that we can do to try to minime or solve that interference will be extreme glad!

 

OBS: I even try to put some ceramic caps (pf ones) that was supposed to be in chassi but was not, to try to minimize the interference, but unfortunely did nothing, image stays with same interference.

 

Thanks a lot

Marcos

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> OBS: I even try to put some ceramic caps (pf ones) that was supposed to be in chassi but was not, to try to minimize the interference, but unfortunely did nothing, image stays with same interference.

 

To add some extra context here, the schematic for the TV shows some small filter caps on RGB and blanking lines (maybe sync too? I forget exactly) that the factory chose not to install. Marcos installed these in the hope that they would.

 

Didn't add mux resistors on this TV as it was already using 75R as the ground resistors on the OSD RGB lines.

 

Marcos....Have you tried undoing the blanking and feeding regular AV footage yet?

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Bom dia Romariu

Tudo blz !

Infelizmente ainda nمo consegui essa interferencia, estou tentando com o Mark da Australia, mas até agora nمo consegui retirar a interferencia.

Tentei instalar uns capacitores minusculos (pf) no chassi que era para estar la e nمo esta, mesmo assim nada de melhorar a interferencia.

Caso se consiga por ai também me da um tok!

 

Vlw abs

Marcos

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Bom dia tambem Marcos obrigado por responder ainda estou na luta de tentar tirar essa interferencia e nada mas qualquer coisa te dou um tok.

Inclusive ja tentei em uma outra muito semelhante a essa LG CP-20K40 e aconteceu a mesma coisa.

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On 19/06/2019 at 2:08 PM, m.andrade1 said:

Marcos! Tudo bem?
Não sei se você conseguiu remover a interferência do seu Mod, eu tenho a solução! Tenho o mesmo modelo de TV e comigo também apareceu essa interferência, um pouco menos intensa, mas estava lá!

Depois de vários testes trocando fios, mudando o ponto de GND da Placa da TV, que não surtiram efeito, o que resolveu foi remover os resistores de aterramento do R,G B, (R54, R55 e R62) e substilui-los por trimpots.  Ao soldar os Trimpots no terminais dos resistores, solde o terminais do trimpots  referente ao GND em outro ponto de GND da placa da TV, não solde no mesmo ponto (GND) que estavam os resistores anteriormente.
 

Marcos! How is everything?
I don't know if you managed to remove the interference from your Mod, I have the solution! I have the same TV model and this interference also appeared with me, a little less intense, but it was there!

After several tests changing wires, changing the GND point of the TV Board, which had no effect, what resolved it was to remove the grounding resistors from R,G B, (R54, R55 and R62). and replace them with trimpots. When soldering the Trimpots to the resistor terminals, solder the trimpot terminals referring to the GND to another GND point on the TV board, do not solder to the same point (GND) where the resistors were previously.

 

ATERRAMENTO.png

MOD WEGO MUX.png

Edited by wegosan
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