Screen is Black, I can see image with flashlight

I would do a careful inspection of both sides of the logic board looking for corrosion damage. Don't forget the display cable and connectors. Review this guide MacBook Air 13インチ Early 2017 上部ケースの交換 you shouldn’t need to go past Step 30. Clean off any corrosion damage you see, if needed touch up the solder joints make sure you use flux and don’t create any bridging.

If that fails to fix things then you'll need trace the logic from the start on the logic board using a DVM and a set of schematics and boardview drawings to isolate out where the backlight power is lost as well as ID the damaged part.

This might be beyond your skill set

@martinrobertson start off with the easy things. Let us know what exact model your logic board is. It should be a 830-00165 but we just want to make sure. Of course, you do need to perform a visual check of the board first. Check for corrosion, as well as missing or burned looking components. The first thing you need to determine is, if you have power to your backlight. For that, check the voltages on your display connector. With your multimeter set to 50VDC (or close to it depending on your meter), Black to ground, Red to pins 3 or 4 and meter in volt mode, you should get around 30V or higher on a good working system. If you do not have any voltage, check the fuse, as well as the power transistors etc. If the voltage is low but there is power, you need to check your boost circuit. Post some images of your board with your Question. That way we can see what you see iFixitでの質問に画像を追加する方法

Save the images for now since you never know what can happen to this answer, so they may disappear :-) Once we know what your tests tell you, we can probably guide you a bit more in regards to the components etc. Nothing is easy but anything is possible. After all, you are coming to iFixit for some help on this and let;'s see if we can at least narrow it down for you.