Q My wife’s MacBook Air has developed a problem with its screen brightness controls. When she presses the F5 or F6 keys to change brightness, although the on-screen HUD changes, the actual brightness of the screen is unaffected. However it can still be controlled normally from within the Displays pane in System Preferences. What is wrong?

A There have been sporadic reports of similar problems with other MacBook as well as some Air models, so this may not be specific to hers.

Most laptops, even Apple’s, have keyboards that are not as robust or long-lasting as those of desktop models, so this could be an electro-mechanical problem with the keys – although, as the brightness control is displayed, that appears very unlikely. You can rule that out by testing whether these two function keys operate normally when in regular function key mode, and are neither hard to ‘fire’ nor ‘sticky’ when pressed.

A few third-party extensions can clash with keyboard brightness control, so restarting in Safe mode, with the Shift key held to stop non-Apple software from being loaded during startup, should enable you to determine whether that could be the cause.

Finally this may have resulted from a recent software update, in which case it may be a bug in that release of OS X. If the MacBook Air is not running the latest version of OS X which it is capable of, consider upgrading it to that.

Updated from the original, which was first published in MacUser volume 27 issue 20, 2011.