OMG!!! Before I explain what happened at the end, I would like to thank to everyone who contributed to the thread, while looking for a solution to this problem!
Now, it is actually so stupid, simple, and at the front of my nose from the very beginning, but...
I trusted the seller in Germany, who gave this turntable to his friend ('electrician'?) prior shipping to me, and that guy has changed the
broken original input connector with this crap...
I had no idea there is the source of all this trouble. Nothing has showed a sign, current flow was correct, so were values checked by V-meter, no heating downstream to the turntable's board, nothing.
So today I found at home one of those China made simple plug-in connector,
and voilà, here's the solution to the problem it shouldn't be blown out of proportion at the first place, if I just knew. WOW what a lesson! That fuse holder won't be needed, here is just for a case if something goes wrong.
Here is the image that shows how current is 15 V on the entrance. Motor runs smoothly and the most important -
transformer stays cool, barely warm after one hour!!!
Now just have to drill through the existing hole on the metal chassis to make it wider, as the new female connector does not fit, and I will certainly not going to buy the original, and spend additional 12€ !
Once again, thank you all who were jumping in with the ideas willing to help! Respect
Sometimes solutions are so simple that is so hard to find them