Yep. I've finished the checking procedure. All the components are staying at the proper position and are connected to each other.
All I get when I measure with the multimeter is the voltage input minus the dropout voltage.
I evenly switched the regulator with another one of the same model.
EDIT: I found what was the ,,problem". As long as the resistors are leveled with few ohms the output voltage will vary very much, but when there are bigger resistors(like 100k, 800k) there is almost no problem.