monitor display shows in half; other side is dark

Hi @danstan

What is the model number of the monitor?

Try shining a flashlight at an angle close to the darkened part of the screen and check if you can detect any images there at all, when the top half of the screen is working.

They will be very faint if they are there so it may be a bit hard to see them

If you can see images then there's a backlight problem with that half of the screen.

Post an image in your question showing what the screen looks like - a picture is worth a 1000 words. Here's how to do this in ifixit Adding images to an existing question