My LG 55LE5400 TV will not show a picture. The screen is black. I was watching a movie and it just went off.

Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electro-medical.blogspot.com/

In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.
Before going further; try a hard reset first. If it does not help you, replace the main digital board. There are two methods to reset TVs. The first is simple to do; a Hard Reset. The other is somewhat skilled; is a Factory Reset (System Reset). To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. If you do this by overnight is better. This procedure will make it a hard reset. If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option. If you wish to get some details; visit the site linked here.

No 24 volts mean a bad power board. You can get a new one from here: TV Parts Universal TV Stands DLP Chips ShopJimmy

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My 32' LG LED TV has suddenly lost picture! The sound is all right but the Screen is pitch black. After switching it on the picture flashes for a second and then the screen goes completely black.

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it is possible that either the lvds cables connecting the mainboard to the lcd panel are destroyed somehow or either the
Lcd panel itself has the problem could you provide some extra info a photo maybe so i can be more helpfull

If you have the same problem with another input such as a DVD player, this TV might need attention by a qualified service technician.

When TVs first appeared, they had an picture ratio of 4:3, which matched that of most movie screens at the time. Terrified of losing their business, movie studios struck back with "widescreen" films using 1.85:1 or 2.35:1 ratios. When widescreen TVs started appearing, they emulated those same ratios, but many TV shows (and some movies) were still in 4:3---and we were eventually left with a bit of a mess. Canny manufacturers, including LG, have solved the problem by allowing you to adjust the picture ratio on the TV to fit the program you're watching. If it's not set properly, however, your image will look distorted or cut off. A quick bit of troubleshooting can fix the problem easily.

1. Press the "Menu" button on the remote and scroll down to the "Option" title (it should be second from the bottom ). Then select "Aspect Ratio." You should see a list of ratio options. You simply need to pick the one which fits the show you're watching.
   
2. Choose the 4:3 ratio for older movies and TV programs. You should see a pair of bars on the left and right side of the screen. (That's okay: the bars keep the program in the same proportion in which it was filmed.)
   
3. Select the 16:9 ratio for widescreen movies and for more recent shows to match their longer width. For some movies, you may see black bars and the top and bottom of the screen. Again, that allows the movie to be shown in the manner it was filmed.
   
4. Pick "Set By Program" to automatically switch the LG TV between 4:3 and 16:9 to match whatever show is on at the time.
   
5. Select "Horizon" to horizontally expand the image onscreen. It will fill the whole screen---eliminating the black bars to the left and the right---but it may look distorted.
   
6. Use the "Zoom 1" option to zoom the image forward. That will eliminate the black bars at the top or the bottom of the screen, though you will cut off the edges of the image.
   
7. Pick the "Zoom 2" button to select a midway point between "Horizon" and "Zoom 1." The picture is stretched, but not as much as with "Horizon," and fills the screen, but doesn't cut off as much as "Zoom 1."
   
8. Use the "Cinema Zoom" button to enlarge the picture to fit the screen. This option allows you to adjust the proportion to your liking, rather than use the set proportions of the other aspect options.
   
9. Exit the menu when you are done and watch your programming normally.
   

Hi...there,
Wow! You guys...must had watching a really....HOt sizzling movie to make it overheating. Hehehe...
Your inverter are fried, need to replaced a new one. If you still under warranties asked LG to send you a replacement. Have a nice weekend!

i went to turn on the tv and the power button don't work

Make sure that the color control level is set to the default or 50% to start with. This should be in the Video menu.

The colour for the tuner and for the encoded base-band video uses a circuit area called the colour demodulator. It is possible that this cirucuit area has failed and needs servicing.

Jerry G.