Hi Eddy, many thanks for your helping documents and comments, and i'm impressed by your sharp eyes and knowledge !!!

-1- Yes i ticked marks to position-back the rotary circuit on top of the motor, but yes i try to test everything on this circuit - including small Hall-effect tripods - is that deadly for them ( my multimeter is a FLUCKE, switched to BuzzerOhm-meter ) ?

-2- I suppose i have to de-solder the GBU12G to test it correct ?

-3- you are right as well for the 3 legs that look re-soldered : do i have to de-solder this component as well and how come is possible to test it ?

-4- i have the "old" contol-board where i plugged by mistake ( at the wrong place ) the rpm information : may be it is easier to check and repair this board ? ( the present board is burning the 2 protective fuses almost instantaneously, the previous one just doesn't work and leaves the fuses OK by the way )

Thanks Eddy for your time and ideas !