Question about Emerson EWL20S5 20 in. EDTV-Ready LCD Television

1 Answer

TV turn on for few seconds then turn off.

I chek the regulators and the switching transistor and everithing looks ok.
I have the service manual and if i disconect the Inverter CBA board i can turn the tv on and it stay on for 10 minutes but no audio. With all conected it turn on and i see the screen with the menu and then off but no sound. Yesterday i was measure the voltage of the IC 602 and 603 with the inverter board disconected and its start to sound for few seconds then off.

I will keep working on it but if you have a suggestion or an answer let me know please.

Posted by on

  • warrior3 Jan 24, 2008

    Thanks but by 09 DEC 07 I post a solution for this problem in
    www.dtforum.net you can find it there too.
    The post is in spanish but i guess you can translate with a translator program. The problem took me about 3 days to find but it was fun. This is a copy of my post:





    Re: TV LCD EMERSON EWL20S5 , SM OR SCHEMTIC,ENCENDIDO POR SEGUNDOS



    on: December 09, 2007, 13:46:27 PM







    Este
    televisor me dio un poco de problemas devido a su falla y a la pobre
    calidad de sus componentes y del board. En conclucion mi falla se debio
    a el capacitor C305 en el Inverter CBA board. La lampara CN302 no
    encendia ni si quiera por par de segundos. Se puede desconectar las
    lamparas y probar una a la vez para ver si porlomenos enciende,ademas
    el IC1202 tiene dos protecciones que tienen que tener 3.4V . Debido al
    capacitor defectuoso al inicio del encendido Q305 detectaba el sobre
    voltage y variaba el voltaje de la proteccion 1 del IC1202 e
    inmediatamente se apagaba. Una prueba que hice fue que desconecte el
    pin #3 en el conector CN404 y encendi el TV y se mantuvo encendidio
    pero se debe tener precaucion antes de hacer esta prueba. Si los
    voltajes de los reguladores se encuentran bien entonces se debe
    verificar el Inverter CBA y sus lamparas ya que estos circuitos cuentan
    con comparadores de voltajes y si una lampara esta defectuosa puede
    causar la variacion y se apagara el TV por proteccion. Esto es bastante
    comun en los TV LCD por este tipo de tecnologia. Asi que buena suerte
    y cualquier sugerencia es bien recibida oK.
    Thanks and keep the good work.

  • warrior3 Jan 24, 2008

    Thanks but by 09 DEC 07 I post a solution for this problem in
    www.dtforum.net you can find it there too.
    The post is in spanish but i guess you can translate using a translator program. This is a copy of my post:





    Re: TV LCD EMERSON EWL20S5 , SM OR SCHEMTIC,ENCENDIDO POR SEGUNDOS



    on: December 09, 2007, 13:46:27 PM







    Este
    televisor me dio un poco de problemas devido a su falla y a la pobre
    calidad de sus componentes y del board. En conclucion mi falla se debio
    a el capacitor C305 en el Inverter CBA board. La lampara CN302 no
    encendia ni si quiera por par de segundos. Se puede desconectar las
    lamparas y probar una a la vez para ver si porlomenos enciende,ademas
    el IC1202 tiene dos protecciones que tienen que tener 3.4V . Debido al
    capacitor defectuoso al inicio del encendido Q305 detectaba el sobre
    voltage y variaba el voltaje de la proteccion 1 del IC1202 e
    inmediatamente se apagaba. Una prueba que hice fue que desconecte el
    pin #3 en el conector CN404 y encendi el TV y se mantuvo encendidio
    pero se debe tener precaucion antes de hacer esta prueba. Si los
    voltajes de los reguladores se encuentran bien entonces se debe
    verificar el Inverter CBA y sus lamparas ya que estos circuitos cuentan
    con comparadores de voltajes y si una lampara esta defectuosa puede
    causar la variacion y se apagara el TV por proteccion. Esto es bastante
    comun en los TV LCD por este tipo de tecnologia. Asi que buena suerte
    y cualquier sugerencia es bien recibida oK.
    Thanks and keep up the good work.

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1 Answer

This TV has a network of diodes connected to a PROTECT-1 line monitored by the control IC. If any circuit pulls this line low, the control IC turns the system OFF. The diodes act to isolate all the circuits from each other, its called a diode-OR circuit.
You can troubleshoot by opening a diode which disconnects a circuit from pulling the line low. I had a hunch the EL backlight board was bad, so after opening that protect line the power stayed ON.

I found a bad .068uF 250V cap on the transformer primary, it measured .002uF. I've replaced the cap and the other two on the other transformers just for good measure.

It probably took more time than the TV is worth, but my friend's Mom will be happy, and thats worth it.
I hope this helps, look around for the service manual, it can be found online.

Posted on Jan 15, 2008

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