Curtain shutter repair on a 13x18 Mentor Panorama

I have bought a 13x18 Mentor Panorama that apparently has an issue with the shutter.
The shutter cocks correctly but once the cable is released instead of opening and closing the curtain it remains wide open and of course it burns the film.
I could not determin (I am not a great tinkerer...) whether the shutter is not completely cocked, or there is any setting which I fail to activate or the shutter is simply broken.
the manual is german/russian in pdf format, I kind of translate it but found no clear indication of the potential issue.
I wonder if anyone has had the same issue with this camera or similar cable release curtain shutter camera and/or is there a reparigin manual or video I can use at least to determine the issue
Thank you in advance for any suggestion