Nikon SB-5000 Reference Manual page 158

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Cooling system
The SB-5000's cooling system effectively cools down the flash head. It
can extend the time before the thermal cut-out function starts operating.
Choose [ON] or [OFF] in the setup menu.
• When it is set to [ON], an operating noise is produced after flash firing. If
this causes problems, set the function to [OFF].
• When it is set to [ON], the batteries may become unusable before the
estimates given (0H-23).
• While the cooling system is operating, the standby function is canceled.
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