Cannot mirror to LG tv using cdmi/thunderbolt iMac conn.

Recently had a lightening strike and circuit board replaced on iMac mid 2011 w.thunderbolt. Previously had mirrored conn. to 37inch LG tv. Now LG replaced with new model LG43LJ5150 and I cannot get the arrangement tab to mirror with the hdmi and adapter conn. to thunderbolt. I have reset NVRAM and done everything suggested on the comments to this problem of now arraignment tab. Is it possible the new LGtv will not mirror? Any other things to check? How could I test the hdmi/adapter cable to know if the lightening strike might have fried it?