Samsung's system does not allow this so the only way back is to replace the board the firmware is on.
There is some issue with Samsungs over the last month or so that shutdown when they connect to the internet.
Be sure to unplug all HDMI cables, then remove power for 5 minutes. Reapply power then do the usual factory resets. Do not connect it to the internet. Apply one HDMI connection and retest.
Since i have upgraded my firmware to T-MX9FMASC for my Samsung LED UA40EH5000RXXT, my LED is having problem with HDMI connection. It suddenly starts shutting down when a HDMI connection is attached. Previously with the old firmware, all HDMI devices were working fine.

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