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Hello and sorry you're having problems. Offhand, ALL of the HDMI processing in your TV occurs on the Mainboard- there are no other boards/parts that contribute to the HDMI processing of the set. That being said, this would point directly to the A Board that you received not being a fully-working part. Where did you purchase this board from please?
You can also try unplugging the set and removing then re-seating all connectors to the A Board to see if that helps, but if those ports are still not working- make sure you're using a known good HDMI cable and also try other sources (meaning Cable Box/SAT Box, DVD player, etc.). Those are the basics and I'm assuming you've checked that already. In that case this means the HDMI ports are bad on your replacement A Board and you'll need to send that board back and source out another.
Feel free to reply back if you need more help, or want to reply back with more details. It does not cost you anything more to reply back once you've rated. Please do rate me positively (at least 3 STARS) and I will continue with you until this is sorted. The positive rating ensures I am credited for my work.
Not sure where you purchased that board from, but I would recommend the folks below as being a reputable source: