This customer sent in their MacBook Air to our store in New York City for our logic board repair service because it had no backlight.
What was causing the issue?
The first thing we have to check on any MacBook that has no backlight is the Backlight fuse. While the fuse may not be the primary issue, it can give us a general idea of where the issue may be. On this MacBook, the fuse measures Open Line, meaning it has blown. Next, we measure resistance to ground on Backlight Output. Resistance to ground on this line is almost zero ohms. This means that Backlight Output is short to ground, and replacing the fuse will not fix the issue, as it will just blow again because we have a short to ground.
Next, we have to figure out what is causing the short to ground. After visually inspecting the board, we see that the LED driver looks fine and the connector looks fine. However, there are some capacitors that are discolored.
How do we fix the issue?
To fix this machine, we have to clear the short to ground, and then replace the fuse as well. We can conclude that the most likely source of the short to ground is one of the two discolored capacitors that we noticed earlier. After replacing both caps, the short to ground is gone. Next, we replace the backlight fuse. After confirming that the fuse is good, we turn on the machine and see that we now have backlight!