Wow, talk about a fix that should be public.
Cut a jumper they missed at the factory. JP852 on the power supply board.
The fix (for backlight strobing):
Remove phillips screws that hold the back black metal cover onto the tv, there's one screw at the inputs area, the rest are all around the outside of the frame. All are in plain sight and no stickers or other items have to be removed to get the cover off.
After you have the cover off, cut a jumper on the power supply board that was missed at the factory.
Jumper location: JP852, it's a small connecting wire between the input and cold area of the power supply board.
There's a Samsung bulletin for this issue, it didn't show up on the repair guys computer. He called them as he thought it could be the panel itself (which requires authorization as it's over some set value), the guy on the line said it's a known issue and there was a bulletin by Samsung.
While I didn't get the bulletin number, the fix is to cut a jumper on the power supply board, something they missed in the factory.
He cut that jumper, put the back panel back on and remounted the tv (it's wall mounted), problem fixed.
The repair guy said every Samsung TV in this class has the same issue, something that was missed at the factory. In my opinion this should be public knowledge and Samsung should be fixing these for free, even for those out of warranty.
A quick google search on the jumper lead me to another thread, with another model that was affected by this issue LN46C630
I also asked about a "buddy's older Samsung TV", thinking of the guy in this thread that said his TV takes forever to turn on, he said that's another known issue with bad cap's on the power supply, easily seen by bulging of the cap's. To fix those the caps have to be replaced, he said that's so common that he keeps a whole bunch of caps for the Samsung power supply's in his repair truck.