I did the tweak on my 50PK550 (North American model, Mar 2010 build) this morning with stunning results (so far).
Following the tips in this thread, I adjusted only VY and Set_Up. Factory presets were 4 and 1 o'clock respectively; I started by turning these to 2 and 7 o'clock (i.e. Set_Up maxed out). Wow! Massive instant improvement! Turned TV off and allowed to cool 45 mins. TV back on, again v deep black level ... BUT suddenly saw too many misfiring pixels (unacceptably noisy-looking picture).
I decided to proceed as follows: sit at my preferred view distance (lately 63") and then throttle back VY and Set_Up, not necessarily til absolutely no pixels misfired, but only until I judged the results to be tolerable in actual viewing. (I figured I was willing to trade off a certain amount of picture noise for better black level -- exactly how much noise, to be discovered by experiment.)
I did all tests in 72Hz mode since on my set the MLL is visibly better than it is in 60Hz. I know in theory it should be the other way round but I'm not the first to report this on the 50" model of the PK550. To get the colour bar patterns, played on PS3, converted to 1080p24 I used an outboard video processor (DVDO Edge); I also tried some HD cable movies and of course Blu-rays.
Eventually I settled into VY 3 o'clock and Set_Up 5 o'clock. If I look very very hard (from 63" away) at the blue and red on the colour bar pattern I can still sometimes barely see the occasional misfiring pixel. BFD; black levels are now insanely good, and besides, I can't see the misfiring at all during a movie. With my bias light on (GE 20W Daylite flourescent strip 6500K) black appears almost as black as the bezel. I don't have a light meter so I can't say what the MLL is exactly. Suffice it to say it's pretty freakin' black. If I wanted to I could probably watch this set in the dark. (I couldn't before the tweak; MLL was way too high for that.)
I watched half of Sin City Blu-ray and was utterly floooooored by the new improved contrast. Other PQ-demanding films which instantly went from blah to wow: Dracula (Coppola), The Spirit, dark scenes in Pirates/Caribbean #1. Can't wait to try more.
I'd like to say a huge thank you to the contributors to this thread. What an awesome tweak. I will post back if I run into any issues in future.
PS: 50PK550 owners: As you remove the back cover watch out for the mini screws around the component video inputs; they're easy to overlook. Ditto for the lone screw near the HDMI ins and the one by the power socket.
"... we wonÂt be stopping plasma production any time soon. We see it going on for another ten years." -- Kevin Lee, VP, Smart TV Partnerships (Samsung), 1/7/11