Brother HL-2700CN Service Manual page 376

(7) Turn the printer on. The printer automatically moves to the rewriting mode and
starts rewriting.
While rewriting the firmware, LCD blacks out and "DATA LED" blinks. Be sure
NOT to take out the CompactFlash card, or turn the printer off until it reaches to
the condition of step (9). Rewriting may be impossible once the writing procedure
fails.
(8) When rewriting finishes, [....Complete....] appears on LCD. Turn OFF the printer,
then take out the CompactFlash from the printer.
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