My 42 inch smart tv has sound but no images, what could be the problem?

Here is a link to the manual and other information, look it up. Product Support

I would say first replace the TV and stop wasting money, next it is likely the LED driver that is causing the problem.

You have to check the audio settings of your tv. There would be n option which allow you to choose the option between internal speakers or external speaker. You have to choose it as external speakers of amplifier.
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LG 42LS5700 - LG.com

www.lg.com > Home > Support > Product Support

LG ElectronicsTV/Audio/Video; TVs; 42LS5700 ... TV Support Landing Page - HDTV/Netcast/webOS 1.0/webOS 2.0 ... Adjusting Picture Settings - webOS 2.0 Video ... quality and convenience of complimentary shipping when buying directly from LG.com. ... Curved TVs · 22 Inch to 29 Inch Class TVs · 32 Inch to 39 Inch Class TVs · 40 Inch ...

Amazon.com: Customer Reviews: LG 42LS5700 42-Inch ...

www.amazon.com/LG-42LS5700-42-Inch.../B006ZH...

Amazon.com, Inc.LG 42LS5700 42-Inch 1080p 120Hz LED-LCD HDTV with Smart TV (2012 Model). byLG. Size: 42-Inch ..... images are nice and crisp when viewing HD content.

Widescreen TV Black Screen - Repair LCD LED PLASMA ...

? 3:41
https://www.youtube.com/watch?v=RbZncfiOXQA
Jul 13, 2011 - Uploaded by FixItUrselfDummy
Fix your tv with black screen blinking light, popping sound noise. ... Watch QueueQueue ... TV Black Screen - Repair LCD LED PLASMA - Problems SONY LG .... I have a 60 inch samsung DPL tv how can I stop the humming or ... What do I do if my tvturns on but its just a black screen so sound no picture?.

Here is what to check when your TV is turned on, power light is ON, but no picture is seen or sound is heard:

1 - Be sure the component you are using (Xbox, Cable, SAT, ROKU) is turned ON.
2 - Check to be sure all cable and cords are securely connected to the TV inputs and component outputs.
3 - Make sure you are on the correct input as some TV's will show a black screen if there is nothing connected to that input.
4 - Unplug the input you are trying to use from the TV (such as an HDMI Cable) and plug it back in.
5 - Check for signs of damage on all cords and cables from the TV to all components.
6 - Make sure the TV is not in ENERGY SAVE MODE, press the button on the remote control to go back to normal mode.
7 - Unplug the TV for 10 minutes to see if there was a temporary one time issue with the TV.
8 - Disconnect the TV from power for 2 minutes, then when plugging it back in PRESS AND HOLD THE POWER BUTTON ON THE TV FOR 10 to 20 SECONDS to try and force the TV to reset.
9 - If after checking all these different issues, you may have a Faulty Power Supply Board, A Bad Capacitor on the Power Supply Board, Loose Wire Harness, or Loose Ribbon Connector in the TV itself.
10 - Most likely when a TV has the power light ON but NO PICTURE and NO SOUND, it is the Power Supply Board that has failed.

BTW, here are solutions for you to play iTunes movies on Samsung smart TV

It sounds that the T'Con board has failed. If you are not familiar with electronics, do not attempt to repair. Whether you suffer fatal electric shock. Instead, contact any experienced service technician, or the nearest service center.

Hi - I'm Tina from Suddenlink. Please check our help site with information and codes for programming Suddenlink remotes: http://help.suddenlink.com/Television/Pages/RemoteControls.aspx

Most likely your Y Sustain panel has gone bad. I would have a qualified service center evaluate it to be sure.

Check this link to find the LJ41-02759A board for your TV. These boards fails quite often and the TV will power ON but with the same symptoms as yours.