Some users power up their Macs to find they are re-living the year of the first moon landing, with the date and time setting reverting to Dec. 31st, 1969. The problem can be temporarily resolved by simply using the Date and Time System Preference pane to correct this setting, but the erroneous date/time may return the next time the system is restarted, causing significant issues with file creation dates, some date-reliant applications and more.
This problem generally has three causes, which can manifest singly or in tandem:
- A faulty PowerBook/iBook primary battery that must be replaced
- Corrupt or otherwise problematic PRAM or NVRAM
- A malfunctioning PMU (power management unit)
In the first case, a faulty or expiring primary portable battery, you may experience a number of other issues in addition to the date reversion, including the system suddenly falling asleep while a charge is still shown, the system being unable to stay powered up without the power cord attached, and more.
Your first step in this scenario should be to re-calibrate the battery, per Apple's instructions in Knowledge Base article #86284. Calibration can be accomplished by first fully charging your portable's battery (look for the "Charged" message in the menubar battery display), then disconnecting your portable from external power and allowing it to run until it falls asleep automatically when the charge is spent. Upon re-connecting power and again fully charging your portable, the battery will be calibrated.
If you continue to experience the date reversion issue after re-calibration, you may need to replace the battery. If your PowerBook/iBook is still covered under an Apple warranty or AppleCare, you may be able to obtain a free replacement. Otherwise, the online Apple Store lists replacement batteries for all portables.
In the second case, corrupt or otherwise problematic PRAM or NVRAM, you may need to reset these two small memory banks via the following process:
- Turn off your Mac
- Press the power button, then immediately begin to hold the Command, Option, P and R keys.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
In the third case, a malfunctioning PMU (power management unit), you may need to reset the PMU -- a small integrated circuit that is responsible for various power-related properties, including scheduling of sleep, charging, and date/time storage.
Instructions for resetting the PMU for various Mac models are contained in the following Knowledge Base articles:
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