Hi! I had problems with my Samsung UN55KS800DFXZA VER AA02 tv. I changed the main board, power board, wifi board, and ribbon cables; but I still have no picture, and no sound.

SOURCE: TV does not turn on/red led flashes 7 times in front

this is common issue with this model and through your troubleshooting is tied to y main board. blinking led on logic main in normal operation. when replacing y main always good idea to replace y upper and lowe buffer boards as they complete a circuit and sometimes replacing one without other could cause additional failure on remaining boards

SOURCE: sound no picture, which component is tcon board? where all audio/video/cable/hdmi plug in to?

for bn94-00963b go and change your backlight inverter

SOURCE: Samsung TV won't turn on- trying to fix it. A challenging problem

I had the same problem. I live in NJ and called the local authorized "service provide" listed on the Samsung website. What a joke. Quoted $350 just to show up, never showed up. So I opened my own TV. Took off the plastic back (10 screws) took off the large metal RF shield (12-14 screws) and noticed a blown component. The markings on the component were KL15L and it is apparently an NTC Thermistor. Obviously it got fried and not knowing if there was other damage I decided to set out to replace the entire Power PCB Board Assembly and not the component. There were two part numbers on the assembled board (BN97-00457E & BN94-00622E). After searching online I also found a suitable replacement number for these (BN96-04896A). I found two places who claimed to have the part or have it on order (shopjimmy.com and vancebaldwin.com). After placing orders with both and having neither come through, I broadened my search and found out that the LNR409D was basically the same model as my LNR408D so I looked for its Power PCB Board Assembly part number which turned out to be BN41-00521B. Google search for that part number showed the item available on ebay. I bought it a week ago (ebay 260311519904) for $144 plus $12 shipping. I removed the bad board an hour ago (6 screws about 7 connectors) installed the new one, plugged in the connectors, replaced the covers, plugged in the TV... AND IT WORKS!
Suggestion: If your TV is out of warranty then open it up (what have you got to lose) and see if the problem is obvious and maybe something you can fix (replace) yourself. The parts, spare boards, etc. are out there if you look.

SOURCE: sound no picture, which component is tcon board? where all audio/video/cable/hdmi plug in to?

I have LNS4692D. Returned from vacation, turned tv on - no picture. Tried turning tv off for 4 hours- nothing. Symptoms are: tv is on - no picture , just sound; menu doesn't show, volume bar doesn't show;E.Saving is working - the backlight is changing from lighter to darker.
Found this website and ordered T-con, otherwise known as the LCD panel driver board, p/n# Bn8101286a ( thanks premtech) from partstore.com for $124. Part number BN81-01286A A/S T-CON Board.
Installation:
1.Remove plastic cover. There is an arrow for each screw that needs to be removed. Make sure to unscrew pins next to VGA port. I've spent some time trying to figure out what else is holding the plastic panel until I found this pins.
2. Remove big metal shield in the middle of tv that is covering main components. This shield is being held by small black screws all around it.
At this point you will see cover of T-CON. Here is the picture
http://www.avsforum.com/avs-vb/attachment.php?attachmentid=118863&d=1220531321 (thanks ldac9). Do not attempt to remove that cover yet. Proceed with a next step

3.Remove metal panel that holds main components. Locate big chrome screws that have arrows pointing to them and unscrew them. Remove 2 more screws on the bottom of the panel that holds it together with a box for cables. At this point the main panel will be lose
4. Carefully start lifting the panel. You will see that there are connectors going from components on the panel to components on the lower panel and T-CON. Carefully unplug these components and raise the main panel.
5. Remove 4 screws that holds T-CON cover. Pull the cover so that T-CON is completely exposed. The cover is connected by thin alluminum , don't hesitate to pull it , but don't rip it out.
6. Once T-CON is exposed you will see 2 red ribbons. I've spent some time to figure out how unplug those from old T-CON board. Here is the suggestion. Don't try to pull it out. All you need to do is to lift small plastic lever that is part of a connector. Then ribbon can be slided out. If not sure what to do, see how this is done on the new T-CON. It has a principle of buckle on airplain safety belts.
7. Remove old T-CON and install new you.
8. Follow reverse order.

I've never fixed TV before , but this was totally successful project.

SOURCE: how hard it is to replace by yourself main board Samsung LN-T4065

You need to do some more diagnosing of the problem. If you get sound and change channels take a bright flashlight and place it again the screen. Look for an image around the edge of the flashlight.
If you see an image that means the LCD controller board (TCON) is probably good.

The problem is probably one of three causes;
1) Inverter board is bad
2) CCFT (cold cathode fluorescent light) are bad.
3) Power to the inverter board is bad. You can also check the connectors.