My Samsung LED Series 6 TV does not have picture but does have sound. Thanks.

Hi Doug, you already diagnosed your set when you said it flickered like a dying light bulb, your LED backlights have failed and need replacing, you should be able to get parts from shopjimmy, stay away from ebay for parts

Inmost of the case,the problem is the LED strips.

To check it, the best way is use a LED tester, if you do not have one, you have to disassembly the LCD panel, unplug the cable between the power supply & the main board, apply the AC power to the TV, you will see the defective strips do not light up.

Sounds like Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main board.

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

If there is no sound comes with on-air programs, and there is only picture, check the settings. That is, if the transmission system at your country is PAL, and you have set the system at your TV to NTSC or SECAM, there will be no sound. Check it. Refer its user manual for details. It will be best to set this option [color system option] to Auto. If so, the TV will adjust the system by itself.
Gopakumar Gopalan Google

SAMSUNG series 6 6400 User Manual Download the user manual to this TV by this site. It has all details.
Electro help

How to turn on PIP in Samsung TV SAMSUNG STEP 1. OPENING MENU SETTINGS


Click here to know about PIP in Samsung TV.
a). Press MENU key ( ) from TV remote.



b). Select Picture option and press ENTER key ( ) from TV remote.



c). Select PIP option and press ENTER key ( ) from TV remote control.

STEP 2. TURNING ON PIP SETTINGS

d). PIP window will open on TV screen. Select PIP and press ENTER key ( ) from TV remote control.



e). Select On option and press ENTER key ( ) from TV remote control.



f). Enjoy watching PIP screen.

Unplug your tv for a few minutes might help if it doesn't, turn your tv on, go to menu, reset to factory settings.