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This is a tricky one until you know the secret. Look at the label on the printer, there will be a "PW" and series of letter/numbers that is the PRINTERS pass word it wants to know to update firmware This isnt the same as the default WIFI pass word (change that one right away). The attached image is the PW for firmware changes and the like so you don't use the wrong firmware.
Sorry, there was a problem. Please try again later.Here's a link to assist with the password for the HL-L23390DW. https://help.brother-usa.com/app/answers/detail/a_id/152494
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