Quoted from C0untDeM0net:I've seen individual led's go bad on the boards both on the playfield and in the back box. It's pretty uncommon though. You can always try getting it warranty replaced. I've been surprised how responsive stern support has been in the past. It is on the main board i believe which may be a while before stern has replacement parts. This is always an option too
https://cointaker.com/products/stern-led-backbox-kit
It's the backlight of the lcd screen... Have to dismantle it to access and repair it.
Surprisingly, it's not your 'run of the mill' lcd screen, it's actually an industrial grade screen. Cheapest I found online is 148 dollars (not as an official stern replacement, but the exact reference used from Innolux)