Replaced display, now blank when was working

Hi there, the external display works with or without the internal display connected. I don't have another internal display to test with. The only other thing I can think of is if the display cable became loose motherboard side? But I noticed it runs underneath the board so would have to remove the board to check.

@f4ll3n If the external display is functioning normally when connected to the computer, and the only thing that's not functioning is the internal display, then it sounds like there's a problem with the installed internal display. It's unlikely that the display cable became disconnected from the logic board because it's typically screwed into place with a small bracket. Can you reinstall the client's original damaged display to see if you get anything like a backlight? That may help you confirm whether or not the new display you are using has an issue.

HI Zachary, I have just realised I have posted this questions twice! (this one was originally rejected).

So the new internal display has been tested by the supplier and is working correctly. The old internal display did have a backlight, and that was no longer there when I reconnected it. So I am guessing it is either the display cable or the board itself. It has now gone back to Apple to look at.

I forgot about the cable being secured via the bracket, therefore it is possibly the display cable?

@f4ll3n Hmm, if the original display no longer shows a backlight either, then that would seem to imply the problem is not with the new display, but rather an issue with the logic board or connection to the logic board. Since the computer powers on and works with an external monitor, it's probably not the logic board that's failing. I think it's uncommon for the cables on these models to fail, but it might be worth reseating the connection to the logic board. Good luck!

@zpl So I have now found out the display has been replaced by someone else in the past so it is possible that the cable wasn't secured properly logic board side (although odd that when I first connected the new display, it worked - and without actually re-touching the cables it stopped working). As I said though, new display is fine.

I have decided not to touch this one myself anymore and will do a self-funded project to re-attempt this repair on another similar model. I have successfully replaced a Macbook Pro 13" display in the past, 2019 model which was more complicated. Apple have only picked up the fact the screen is a 3rd party but haven't mentioned any other issues so will be interesting to see what they discover on the repair itself.

Will post up here on their findings just so there is some conclusion to the post. Thanks for all your helps thus far.