I HAVE A RCA 42" LED TV. I RECEIVE MY SIGNAL FROM AN ANTENNA. I CAN ROTATE MY ANTENNA, SCAN THE TV FOR CHANNELS, AND THIS WORKS FINE. THE PROBLEM IS IF I HAVE TO ROTATE THE ANTENNA FOR OTHER CHANNELS, AND THEN RE-SCAN, THE TV LOSES THE ORIGINAL CHANNELS STORED IN MEMORY. IS THERE ANY WAY TO MANUALLY ADD CHANNELS TO THE TV, SO THAT ALL YOU HAVE TO DO IS ROTATE THE ANTENNA TO THE DESIRED CHANNEL, WITHOUT HAVING TO RE-SCAN THE TV AGAIN. ALSO, MY TV DISPLAYS THE TIME IN MILITARY TIME IN THE TV GUIDE DISPLAY. IS THERE ANY WAY TO MAKE IT DISPLAY IN AM / PM TIME INSTEAD.

SOURCE: have a 42 in rca lcd tv ,hsound but no picture

IF the set is under warranty, you should return it.

Do this to see if your set is "sending" the image to the LCD panel.
1) What the set on take a bright flashlight and press it against the screen.
2) Look for the "image" moving around the edge of the flashlight.
3) If you see the "image" then the problem is in the inverter/CCLT or the power to it.
4) If you do not see the "image", you should look at the LCD controller(TCON) for the problem.

SOURCE: no signal display on rca 42" lcd

If you have tried other input jacks and cables with the same result, then yes, the input/output board is defective or buggy.  Sometimes a power drain can clear this up as well so it's worth a try:
1. Unplug the product's power cable so the device is not grounded to the house. 2. Press and HOLD the product's own power button for 1 minute to drain the capacitors. 3. Plug the product back into a wall outlet and try to turn it on.
Note: This procedure works with battery operated devices as well so remove the batteries and hold down it's power button.  Electricity can remain in capacitors and on circuit boards enough to prevent normal functionality. By clearing the residue electricity, your product will have a fresh start and many times this will resolve a buggy or non-responsive device that appears to be dead.
If this doesn't resolve it, service would be necessary.

SOURCE: I just purchased the RCA model L32HD31R.

I had the same problem and finally sloved it. You have to leave the input channels ( Vid1, Vid2, SVid, Cmpt, HDMI, etc ) in the In Channel List. So push the INPUT button, go to VID1, press Menu, go down to List & Labels then check In Channel list. Do this for all the inputs and then run your Channel search again. I hope this works for you. It did for me.

SOURCE: 42 RCA TV flashing unusable signal

Ur backlight video board it dead,must replaced.

SOURCE: RCA LCD TV L42wd22YX5 - Gets unusual signal to all inputs

Tries Ebay.com,Shopjimmy.com for used signal tuner main board.