Mitsubishi HS-U747 Owner's Manual page 34

Timer Recording
Memory backup
If the VCR is without power for 3 minutes or less, it will retain the
clock and the programmed settings. The VCR must have been
plugged in for at least an hour beforehand to charge this backup.
If the power is lost for more than 3 minutes, the time and the
programmed settings will be lost.
If you have set the Auto Clock set setting of the Set the clock
menu to ON, the auto clock function will automatically set the clock
again when power is restored.
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