I was recently forwarded an email from a customer who is having issues with his portable computer waking from sleep, and sometimes even going to sleep. He, like many people with similar issues, wants to know why. Unfortunately, there is no one-size-fits-all solution, and sight-unseen, there’s no real way to diagnose the machine. Since it’s such a common occurrence, though, let’s talk about possible scenarios.
For a machine not waking properly from sleep, there are a few basic troubleshooting steps that one can take before bringing the computer in for service. They can try resetting their PRAM, which clears out the Non-Volatile RAM that may have corrupt settings stored in it. Resetting the System Management Controller or Power Management Unit (depending on the machine) is the next step as that clears out potentially corrupt preferences in how your system is controlling power.
If neither of those works, or if it only works temporarily, the next step is usually to try an Archive and Install of the system software, or if you have a good backup and want to really be thorough in your troubleshooting, you can try an Erase and Install. There are a few folks out there who believe an Archive and Install is the placebo equivalent of a school nurse taking your temperature for a broken leg, I firmly believe that is not the case and have seen many a bizarre software glitch fixed with a simple Archive and Install. Fresh operating system = Good Times.
So let’s say you’ve done all of that, and still your machine doesn’t wake properly from sleep. My next troubleshooting step would be to try known-good RAM. RAM can be a sneaky culprit as the processors are constantly transferring information to and from it for quick access. If the RAM is failing, this can cause software corruption. This is particularly frustrating when one has a system that is constantly becoming corrupt but always resolves temporarily after an Archive and Install. While there are plenty of at-home memory tests out there, they can often produce false-negatives (and even in rare cases false-positives). Want to rule out memory? Try running the machine with a fresh chip, run another Archive and Install and see if the issue reoccurs.
Have you now done everything above and are still having issues? It might be time to bring it in for repair. While at this point some technicians make the mistake of jumping right to the logic board, often times sleep issues are caused by a defective sleep sensor. This is more likely in the case of a machine that puts itself to sleep (as opposed to one that has trouble waking up). In rare cases, a defective temperature sensor or flex cable can cause sleep/wake errors as well.
There are two more machine-specific hot tips to check that could help your technician diagnose the issue. First off, if you have a 15” PowerBook that is putting itself to sleep, check the Console logs and if you see “PMU Overtemp” you most likely need your top case replaced (where the sleep switch on that model is located). Have a MacBook Pro that’s waking up in your bag or when you pick it up closed from the right-hand side? That most likely needs a top case too.