If the Brother printer switches itself off again immediately after it has started up, it may be possible to trick it with the open paper cassette.
Question: My Brother printer shuts down immediately after switching on. Then it only reacts again after I have unplugged it for a long time – in the same way. How can I use it again?
Mac & i replies: The manufacturer support provides two odd-sounding solutions. In any case, you must first leave the Brother printer unplugged for at least half a minute. In workaround 1, press and hold the power button and then plug in the power cord. Do not release the button until the device has fully booted up. If that doesn’t work, repeat the process up to three times, according to the manufacturer.
For solution 2, pull the paper cassette completely out of the unplugged printer. Then plug in the cable and press the power button. Do not push the tray into the device until it has fully booted up.
In a comparable case, we proceeded in a similar way, unplugged a Brother MFC-J4710DW for a few minutes, opened the top flap including the scan unit, plugged in the printer and switched it on. Due to the open flap, the device displayed an error message and did not shut down immediately. Then he could be used normally.
If you want to get to the root of the problem, replacing a capacitor might help. At least that helps according to a handicraft guide on iFixit for the MFC-J4420DW model. Effort assessment: “difficult”. It works similarly for some other Brother printers.