fixable depends on the problem. there are four basic things to kill a backlight
blown microfuse on logic board (usually due to a failed/shorted cable)
bad sleep/backlight cable (very common)
bad inverter
bad backlight in lcd panel
the second is very common. usually the backlight starts cutting out at certain angles of the lid being opened and gets worse over time. hard to verify if it's failed completely. very cheap part but high labor. inverter failure is next most common, cheap part but somewhat high labor.