Often you walk into a casino and these particular games have the darkest screens...yep, the inverters are going on them.
Video slots are like light bulbs....they don't last forever.
Sometimes you can make an rough guess given themake and model of your LCD screen, that'll help a guess how old they are.
You can also roughly guess how long they should of lasted pretty much from the tags on the side of the machine too.
Sometimes there's ancient labels on the back of the monitor showing the date of manufacture as well.
Lifetimes of LCDs vary from model to model....much depends too on how they were stored after they were removed from the gaming floors....I've seen de-commissioned machines stored in leaky wooden unheated sheds at 30 below zero up here in the northeast.