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It is probable that your smart remote is either not compatible with the newly installed main board's revision level (since it was not an exact replacement down to the revision level.)
Or else, there is some other problem.
It might, for instance, be a coincidental failure of your smart remote. In which case, checking the remote, its batteries, etc., would be the right thing to do.
With certain types of remote control, it might well be that you will need to re-register the remote to the 'new' TV - 'new', in that its identity, as far as the remote is concerned, probably has changed, with the change of the main board.
Is the remote in question the one that came with the TV? or is it an added-on remote, or a Harmony remote, or similarly not original to the TV?