Left joy-con not connecting on bt and handheld.

Hello,

So i bough couple damaged joycons and one of them i have no idea how to repair or where is the fault.

It does not connect both on bluetooth and when in console. In fact it does not light up when im pressing buttons to go into pairing mode. What is strange is that, when i put it in console and get it out and press button, then it starts blinking (console also sees that i attached something but that might just be physical indicator going off )- its in pairing mode, but is still not pairing. It will let me try to pair it 3-4 times and after that will not react to button pressing any more untill i put it in console again. What is even more curious is that it react on every single button but…the pairing button.

Here is the list of what is NOT the fault, i checked all i could.

1) Battery is ok, switched it and its the same.

2) Railing connector is ok - same as above

3) All ribbons are ok - as above

4) Its not bt antene - solution here on ifixit is to put electroconductive foam on antene, but my joycons already have it, my guess is they are later release.

5) There is no water or physic damage. I don’t know the history of the controller but inside it looks perfect and outside just couple scratches.

My guess is, its faulty board but how do i check it and what exacly is responsible for both br and railing connection? There are prob no spare parts but mayby in time i will get another faulty one that i cant repair and will switch chip or what ever it is.