This TV turned on with no backlight. I found four intermittent LEDs on one strip and replaced them with 3V Samsung compatible ones. To turn down the backlight, you need to go into the service menu. For this model, with the tv on, push source-2-5-8-0 on the remote and the backlight level is under Panel Settings. I set it to around 55. This value needs to be set on EVERY input and may apply to only the current picture setting (Standard, Energy Saving, Dynamic, User).
Update: I got another of this model in. I was having repeat failures on a bottom strip. Since it was difficult to find even a used strip (part# DLED55LS 5×10 0005 A-1 and A-2), I ended up replacing every LED module on that strip.
With this model there is a setting called DLC (Dynamic Light Control) which is on by default. I would turn this off so the backlights do not go bright in a bright room. You need to to set this on every input. I also found the backlight settings very high so adjusted the backlight level to 10. Again this needs to be done on every input.
Update 2: I replace every LED on the strip and they are still burning out after several hours. This model appears to run the backlights at very high current even with the backlight level turned down. I have ordered some 2W (700mA) replacement LEDs since the strips can’t be found online.