SamyGO

Hi there Samsung H6400 owners.
My story:

I have 6xSamsung TV different models since 2009 till 2018.
This week the model 48H6400 bought in 2014-2015 stopped recognizing any of the 4xHDMI's.
I have tried everything that can be done to fix it: software wise, different hdmi cables, different sources, factory reset, Service menu nothing can be done to FIX the HDMI no signal problem.
So I googled about a week on what can be done to my tv and I found that the only thing to do is to change the motherboard (not the tcon, but the motherboard).
I want to specify that EVERYTHING else works on the TV except HDMI. 3D OK, TV channels OK, usb OK, etc.
Also the Wi-Fi does not work for 2 years (I believe after a firmware update but not sure) or so but I do not need the wifi and it's not important for me, I only need the HDMI since I am using the TV to a PC source for games and movies/tv-shows nonstop, and occasionally Tv channels.
So my question is this:

Will a motherboard from a different SIZE TV and model work? not different SERIES but model?!
For example: from a SAMSUNG 40H6500 TV to my SAMSUNG 48H6400?
I have a friend who is willing to give me his motherboard and he will have mine since he does not care about HDMI at all, only TV channels.
Also my second question: are the motherboard from different size but SAME MODEL SERIES compatible?? ex:
32H6400, 40H6400, 48H6400, 55H6400 are these motherboards working for any of this models? like putting an 32H6400 motherboard to an 48H6400 model?

I am asking this question here for an expert or advance user or someone that really knows this or tried this because I can search on google all day and see that the motherboard fits and compare the specs and say yes I BELIEVE it will work.
I need a correct answer to know what to do because I do not have the possibility to buy the EXACT motherboard for my TV.
Would really appreciate an response from someone how has this type of knowledge.
Thank you!

LE:
The Samsung H6500 improvement in incorporating the dual tuner, there aren't more differences with the H6400 model.

So with this difference wound the motherboard swap be compatible? would the tcon board give errors? does this board have to be swap also? or it will work by just swapping the motherboard and be compatible from the 6500 to 6400 model?

you can try but you will need to take a pictures from service menu to change the values later. Specially front color and panel type and maybe some more. After you back up everything you can swap the main boards.
you write that the Wi-Fi doesn't work for you did you try to unplug it and check if hdmi start work. Also if you have solder skills you can try repast IC (silicon images) which control HDMI it's close to them.

I think less headaches is swap entire TVs and you can pay or get paid in beers/wines/services for each inches you changed

@notengo13 thank you for your reply!
I haven't touched anything on the back of TV, just disassemble the back panel support, will make a photo tomorrow.
Wifi does not work since 2018 if I remember correctly BUT I haven't tried your suggestion but for sure this will be the first thing that I will try tomorrow because I just asassemble the TV back to watch some movies from USB.
For the IC component I watch this video but there is an plastic glued to the IC and I don't want to make it worse:
https://www.youtube.com/watch?v=SGf8FEjGlVA
Off course it's an old TV and I thought about buying a new one just want to try to fix the HDMI with a motherboard, I have to try,if I fail and don't succeed then I will buy a new TV, but I have to try.
Thank you again for your reply!

I have disconnected the wifi module and bluetooth module sadly the result is the same NO SIGNAL on HDMI.
Here is the picture from my TV:

Also yesterday when using USB stick I have a "corrupted" background in menu like this:

Still this does not affect the picture or playback of any video format, works ok.

My only concern is this:
Do I need the change the motherboard to fix the HDMI no signal?
Or do I need to change the tcon board to fix the HDMI no signal?

Would the HDMI work again with a new motherboard? or a new tcon board?
Witch component is responsible for the HDMI signal?

I would appreciate an answer! Thanks!