Snowy screen/ hdmi non-signal

I got an brand new 4K/Dolby atmos 64gb unit a couple of years ago, i started having problems straight away sometimes when pressing play the episode will come on soundwise but have a snowy screen!, and often even during the episode it will lose signal altogether and the tv is looking for a connection, so i got in touch with apple and they took mine in for repairs but I’m certain they gave me a new unit! Either way when the new one had arrived i stored it away because i had already brought my 32gb down from upstairs and that was giving me uninterrupted snow screen free tv, working perfectly in fact, until i decided to sell that one and replace it with the brand new Apple TV 64gb or repaired version i had got from them a year before and again right away snowy screen and cutting signal out from day one, bearing in mind i used the exact same high quality hdmi lead for both of the tv versions and it only does this on the 64gb, but because i had waited so long to plug it in apple won’t do anything about it now. Ive tried a heat sink fan but to no avail, any ideas anyone?