iPhone 6 plus is dead but working under Itunes normaly

Hi friends :-)

I have strange problem and need help before I will start changing U2 or other parts.

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I have one Iphone 6 plus what dont want to start - black screen and no charging. 2 days ago during charging it was a sound at started charging but it was many sounds like connecting and disconecting. Its meen at I connected and this song was coming a few times by self with around 2 second breaks.

The main board was so hot so I diconnected and now is no song and no charging by wal charger - only chargin by Itunes...

That I can understund is dead BUT - working normaly on Itunes !!!!!!

Itunes see the phone and is showing all details/pictures etc ... it was possible also to restore without problems and the most strange is that phone is charging battery when is connected to Itunes.

I have only info that phone is ded after battery changing or screen - no wather problems.

Someone have idea what first I have to check or change ??

I connected other 3 LCDs and stil same $@$* and I connected this LCD what is instaled to other phon and all OK.

Something wrong with phone but what ?? Some indeas what I shoud check ??