TV turns on but only the backlight lights up. No sound no picture.

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Panasonic Viera

Repair guides and support for Panasonic's Viera line of televisions.

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J Mac @jvmccallum

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投稿日: 2018年9月26日

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TV turns on but only the backlight lights up. No sound no picture.

Hi,

My Panasonic Viera model th-l42et5a (smart TV) switches on without issue but I get nothing but a black screen, I cannot get any menus to come up, the backlight is on. I have not heard any sounds come from the TV at all.

What I have tried so far:

Reset TV (Vol down + Menu button)= no reaction.

Unplug TV for 1 min then hold P (Menu)+ Vol down and power on= no change.

Unplugged TV for 10 min and hold power button for 1 min, then plug in= no change.

Attempt to put tv into Panel test mode by Holding Vol down+ pressing Option button three times in 2 seconds= This causes LED light to blink red/green but there is no change on display.

If I disconnect the Left ribbon cable from the ) Tcon board(leaving RHS connected) I get a half white screen on the LHS and a black screen on the RHS.

If I disconnect the Right ribbon cable and leave Left connected there is no change on screen (stays black)

Any ideas?

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do this apply for all brand of TV mines LG50LN5400

David Alcazar さんによる2022年2月18日

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oldturkey03 @oldturkey03

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投稿日: 2018年9月26日

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@jvmccallum

start by trying all input sources. If there is no change then you have to check the main board. Both video and audio are processed by this board. From what you are saying, it sounds like that is the board that failed.

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Thanks for your answer, my logic suggested that this is the most likely failure point except for one the fact the TV also stays blank during the panel test.

Apparently the panel test mode runs from an IC in the panel (or tcon board).

From the service manual-

7.3. LCD Panel test mode

Purpose:

To find the possible failure point where in LCD Panel or Printed Circuit Board when the abnormal picture is displayed.

How to Enter:

While pressing [VOLUME ( - )] button of the main unit, press [OPTION] button of the remote control three times within 2

seconds.

How to Exit:

Disconnect AC plug from wall outlet.

How to confirm:

If the abnormal picture is displayed, go into LCD Panel test mode to display the several test patterns.

And then, judge by the following method.

Still abnormal picture is displayed: The cause must be in LCD Panel.

Normal picture is displayed: The cause must be in A board.

(Board A= Mainboard)

So potentially this TV has a bad panel and a mainboard?

J Mac さんによる2018年9月26日

Possibly, but you can replace the main board just not the panel (easily).

oldturkey03 さんによる2018年9月26日

I replace the lights the power board and the main board I can the back lights on no sound no picture, the screen is lit alight blue but that it,

David Alcazar さんによる2022年2月18日

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Thanks for your answer, my logic suggested that this is the most likely failure point except for one the fact the TV also stays blank during the panel test.

Apparently the panel test mode runs from an IC in the panel (or tcon board).

From the service manual-

7.3. LCD Panel test mode

Purpose:

To find the possible failure point where in LCD Panel or Printed Circuit Board when the abnormal picture is displayed.

How to Enter:

While pressing [VOLUME ( - )] button of the main unit, press [OPTION] button of the remote control three times within 2

seconds.

How to Exit:

Disconnect AC plug from wall outlet.

How to confirm:

If the abnormal picture is displayed, go into LCD Panel test mode to display the several test patterns.

And then, judge by the following method.

Still abnormal picture is displayed: The cause must be in LCD Panel.

Normal picture is displayed: The cause must be in A board.

(Board A= Mainboard)

So potentially this TV has a bad panel and a mainboard? — J Mac
Possibly, but you can replace the main board just not the panel (easily). — oldturkey03
I replace the lights the power board and the main board I can the back lights on no sound no picture, the screen is lit alight blue but that it, — David Alcazar

Lemine @lemine 評価: 1 · Answer 1 · 2022-06-28T00:52:28-07:00

Lemine @lemine

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投稿日: 2022年6月28日

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Same issue here in 2022 when 3d TVs are not available anymore... I'm guessing something has overheated over time.. is there anything that can be done?

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Panasonic Viera

TV turns on but only the backlight lights up. No sound no picture.

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