Apple has released a fix for a flaw that saw certain MacBook and MacBook Pro owners struggling to charge their devices after buying a replacement power adapter.
According to Apple, the problem occurs when new 60W or 85W MagSafe power adapters are connected to the MagSafe port on certain older MacBook and MacBook Pro models. A change in the connector, from a straight configuration to an L-shape which helps to prevent fraying of the cable and overheating, seems to confuse the laptops - and in some circumstances results in a failure to charge.
The models affected are 13-inch MacBooks from late 2007 and the entirety of 2008, and 15-inch and 17-inch MacBook Pros from early 2008 - but only when the original MagSafe power adapter is replaced with a new, L-shaped model.
For those affected, the news is good: Apple has determined that it's not a physical problem, but a software related one - and has issued a downloadable firmware update for the affected machines that resolves the issue and allows the new power adapters to charge the older machines without a problem.
In order to install the upgrade, the machines must be running an up-to-date version of Mac OS X - either 10.5.8 or 10.6.4, depending on model and age. A slightly bigger issue is that the update can't be installed unless the machine is connected to the mains or has at least 25 per cent battery left - and if you're trying to upgrade the firmware because your device isn't charging, that result in a slight bootstrapping issue.
If your device won't charge at all, and you're unable to install the update as a result, Apple has released a guide to resetting the SMC (System Management Controller) to allow temporary relief in order to install the update.