MacBook Pros suddenly shutting down when disconnected from power adapter; not running from battery -- more fixes

We previously reported on an issue where various Apple portables suddenly and unexpectedly power off under differing circumstances, including but not limited to: disconnecting the unit from external power while a battery charge remains; putting the system to sleep either while a power adapter is connected or there is a battery charge remaining.

In particular, this issue has plagued some MacBook Pros, which suddenly shut off whenever disconnected from external power and refuse to operate from the battery. When systems affected by this issue are powered on while disconnected from an external power source, they briefly begin to startup then power down immediately.

In most cases, the battery status indicator reports a full or partial charge, and the Apple System Profiler reports a normal battery connection and capacity.

We previously noted a bevy of fixes for this issue, including resetting the PMU, disconnecting external devices, resetting PRAM and more.

An in-house MacBook Pro recently began exhibiting this issue, and the fix that eventually worked was resetting the PRAM with a twist. Apple indicates that resetting the MacBook Pro's PRAM requires holding down the Command, Option, P and R keys at startup until two restarts occur. However, we found that waiting for three or more startup chimes while resetting PRAM resolved this issue where waiting for only two chimes did not.

Note that we also continue to receive reports indicating that resetting the MacBook Pro's PMU resolves this issue. Resetting the PMU requires the following steps:

• If the computer is on, turn it off.
• Disconnect the AC Adapter and remove the computer's battery.
• Press and hold down the power button for 5 seconds and then release the button.
• Reconnect the battery and AC Adapter.
• Press the Power button to restart the computer.

Feedback? Late-breakers@macfixit.com.

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