Ok, I am doing this too. I thought it would work right away but I was wrong.
I have a 6 series LNXX650 I think TV. I built the ex-link cable like the one above.
I am complete Newb when it comes to serial and terminal etc. So correct me if you see error. With hyper-terminal connect when I turn the TV on I receive a bunch of hex lines. So I assume my cable is working. Yay.
I tried sending hex for "J" for power or "n" for power off like doc says for the plasmas, and I get no response back and no work.
Then I try sending commands I found for DLP's in samsung manuals. Here is the Links to them:
[Link: akamaipix.crutchfield.com] Page121
and
[Link: akamaipix.crutchfield.com] Page222

Both have same commands for on and off, so I send:
08 22 00 00 00 00 D7
(8)(34)(00)(00)(00)(00)(215)
and also
08 22 00 00 00 00 D6
I manually did the Check-sum and came up with D7, and a program i put the values in gave D6.
I try enter the raw values with alt to convert to hex, like alt 34 then let go of alt and it prints 22 in hyper-term.
None of these got any response back from the TV.
Then I also tried "RS232 Hex Com Tool", basically setup to send hex easily, I try some commands like above, no response.

I go into the TV service menu, Hit Mute, 1, 8, 2, Power
The first Option on the top left "OptionByte" I hit enter to bring up new menu,
Near the bottom left it says "RS232 Jack", my default option when I first went in was "Auto Wall" which I assume is for sending remote commands out for wall control, I want commands to go In.. So I try..
"AV Control", "Auto Wall", "Hotel", & "Clone Box"

I try to send the above commands on each, they all look about the same when I power up as far as hex be sent to me. None of them respond with anything I send.

I did read on another forum someone doing exlink on maybe a plasma or dlp and they could not get any responce until they sent the tv the "right" codes.  So maybe its my codes or I am just not sending them correctly..  Any help?

Edit: Also I am aware that you cannot turn the TV on, I dont care about that. I need my HTPC To turn my TV off when the screensaver goes on, and not turn it back on. So if I were to use a IR blaster I would need to use the discrete off code to keep it from going back on if somebody bumps the mouse and the screensaver sets the code off again. I would much rather not use Blasters On my Nice TV.
The RS232 Settings I did not try was "Debug" and "Dealer Cali"