Thanks for the answers. I've inspected well the board and i've discovered that some capacitors on the logic boards are not in good state. Since this i've replaced all of them.
I'll add some information for the users of the forum, i hope that could be useful for everyone.
For the ones that should do this work, these are the capacitors that you need:
Main PCB C26 1uF 50v C27 10uF 25v C28 10uF 25v C30 10uF 25v C40 47uF 16v Power Board C1 10000uF 16v C2 100uF 16v C3 2200uF 25v
Note that there are different versions of the board, then the code could be different, but the capacitor values are these. Take care about the orientation of the capacitor pins.
I've ordered the C1 capacitors since i haven't it, then i'll recheck all the voltages after replacing the C1.
It's important that the power board provides the correct voltages. This are some tests that are on the service manual. If the voltages are the ones indicated here, then the power board should be ok:
The i'll check again my voltages after my C1 capacitor will arrive.
I've checked the continuity of a lot of lines, and it seems to be good. Since i must wait the Q1 and Q2 transistor too, i've made a picture with all the IC where i've indicated all the pins that could be useful to check the voltages. I've found the ground through a multimeter (as you've adviced, i've checked the continuity between the ground of the board and those pins) and i've also checked all the datasheets of those IC to check their correctness and the voltages of the other pins.
You were right!!! They have a strange pinout and also strange voltages!!!
NOTE: the black pins are the GND, and i've written the value of the Voltage near the red pins!
I'll give you other updates after the order of my components will come! Thanks!