Just installed a backlight from kitsch on one of my gameboys, it used to have no vertical lines and the ribbon cable was in perfect condition. After installation, the backlight turns on as expected, yet nothing is displayed on the screen. Fiddling with the contrast dial does nothing. I opened it again to look at the ribbon cables for breaks, and everything seems to be about as good as before. I'll be taking some pictures on sunday or as soon as I can get my hands on a camera that's not total shit, but I was just posting early to see if someone had any suggestions. Thanks!
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The darker side has to be towards the screen, what it sounds like is no polarization film, but these backlights come with the film. Try flipping your backlight around.
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Puerto Rico
Turns out I had removed the polarization film in the step where it said to remove the protective plastic film.
The contrast now works, But I still can't see anything onscreen. 
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Ciudad de méxico, MX
You have killed the ribbon cable, or the things that are beneath the screen, my best guess
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KC
I've done the same thing, yes probably ribbon cable. sucks big time after you go through all that trouble
1st try heating the front accesible ribbon cable and seeing if that helps, then applying pressure on the back ribbon cable that is on the backside of the lcd.
try using the leftover foam pieces
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Puerto Rico
I did put the foam pieces back in.
When you say heat, do you mean full soldering iron heat or...?
I really don't know where the break could be, I was so careful and the ribbon cables look unadamaged...
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KC
soldering iron heat on the front ribbon cable connection
and when I say replace the foam pieces, I mean, use those foam pieces to apply pressure to the the contact points of the ribbon cables and lcd.