While I have your attention - you don't have any guesses what the story would be with a Samsung HP-S4253 plasma panel? I believe it's a 2007 model. It has a similar port called "SERVICE 2" - is this likely 3.3v ttl?
Nope

. If it's named "Ex-Link" - you should expect regular +-12V RS232 (just a "rule of thumb", I wouldn't be surprised if there are some exceptions).
If it's labeled otherwise ("Service" etc.), all bets are off - could be pretty much anything, TTL level (3.3V or 5V) RS232, regular +/-12V RS232, or something entirely else. Usually, it tends to be 3.3V (or 5V) RS232 in 2008+/A-series models and up.
For HP-S4253, there is service manual available with detailed schematic diagrams (
http://elektrotanya.com/samsung_hps4253 ... nload.html). According to the page #70 ("ANYNET & SERVICE I/F", utilizing MAX3232 voltage level converter) there are two separate, external, 3.5mm (?) regular +-12V serial ports on this set. No indication if any of those 2 ports may support Ex-Link protocol or not (I guess not).
Able to be powered on?
I dunno.. one port (called ANYNET) seems to be some kind of predecessor for HDMI CEC (Anynet+) I/F; perhaps it does support power-on? But not likely; looks like it goes (more or less) directly to the S5H2111 SoC, which is probably not active at all while TV is in standby mode.
I think this TV set can also be powered up by PC/VGA port - but it would not be very convenient solution

. Or, if you are willing to open it up and solder some wires, you can probably hijack KEY1/KEY2 (CN405 connector); shorting KEY1 to GND usually does the trick (at least in some A,B-Series models models I'm familiar with; YMMV).