Screen dims then turns off after certain angle

Hi, my 12" Macbook (2015) has developed a problem where the screen turns off after opening beyond a certain angle (at the moment about 60 degrees). It works normally if I only open the screen slightly or with an external display, but when attempting to open the screen beyond a certain point it starts to dim then completely turns off.

When it turns off the laptop still works with an external display and sound still plays - just no image at all on the monitor. Closing the laptop to put it to sleep then reopening gets the screen to turn back on.

Any ideas what might be the problem or if this is fixable?