First make sure that the toner cartridge is fine and enough toner (which I think is ok, but still no harm in checking)
LSU is inside the printer and to locate that you need to remove the outer covers of the printer.
Exploded View of PartsFrom the above link you can check Item Main Assembly (Page-2) and Part labled 4 is the LSU.
You may need repair manual to disassemble the printer. However, it can be done intuitively, if you are comfortable with working inside such devices. IF NOT, I recommended that you may contact authorized service professional.
Hope it helps! Good Luck!
CreativeTECH