My iMac 27" late 2015 i5 thunderbolt2 ports are dead

i got thunder strike directly into my house and it totally killed my second port of tb2 with my external monitor that was connected via hdmi cable and hdmi to minidp gender. it also killed external monitor's port and even hdmi to minidp gender(found out used hdmi cables are functioning by testing it with my other computer).

even first port of my imac's tb2 is half way dead. it does work, but would give a crazy amount of screen noises that moves around. white dots all over the place and seems to thrive even more at a darker sides of screen. so did try giving DP to minidp cable to connect same monitor and it does work, but on screen saver screen the movement of animation is with incredible low frame rate which wasn't the issue before. i tried getting a caldigit ts2 to expand ports from just one thunderbolt thinking it would work since ts2 carries it's own 12vdc power but no. it didn't work at all, from front pannel of ts2 the usb port could give my iphone charged with 5pin cable which is normal because powered ts2 itself could do that but none of back pannel's port would work on ts2 even knowing that it's properly connected to imac by it's blue LED lit up.

then i went checking system information to see whether if it can least indicate that thunderbolt is connected to something. but sadly no again. i tried giving external monitor alone which works but it says no device connected, samething with caldigit ts2 and also tried my zoom tac-2r audio interface which is tb2 bus powered device and result is still no. and also found out that my half way working tb2 is not even able to give enough power to boot up bus powered audio interface which was never the issue before.

so i'm guessing it could be problem caused by dead diodes not giving out proper voltage flowing inside there but then again i'm not an expert on it so who knows..

what can i try out myself to determine further more?

and also, id like to know if late 2015 i5 board is replaceable with 2015's i7 logic board since i'm only getting one i7 board at used market at $250 and replacing board myself wouldn't be a problem since i know thunderbolt ports are attached at logic board so it's not replaceable if that's the issue (which i kinda doubt to be an issue tbh)

either i could take it to a unofficial local tech who can work wonders on mac if diodes or any replaceable components seem to be an issue here but if not, id rather get 2015 i7 logic board and swap it in if it's compatible with 2015 i5 imac.

please help! thx..

okay, heres an update, after having caldigit ts2 connected even first port of tb2 is for some reason not able to give any signal to external monitor which was just fine before having ts2 hooked. at this point i might just get emc2834 i7 if its replaceable with i5 board since i suspect there might be other damaged parts inside. pls let me know if the board is replaceable!!