Problem with shutter with Mamiya rb lens

helo everyone.
i just got a mamiya rb and there seems to be a problem with shutter on the lens. no matter what speed i choose, when i trigger it the leaves shut close down immediately, even wheni put the speed on 1 or T.
what could be the problem? thanks in advance!

Would be hard to tell until it is apart.

the lens doesnt open the shutter when its off the camera as sell.

Make sure the selector on the side of the shutter is set to "N" (for "normal") instead of "M" (for "mirror up"). If the latter, the shutter will close when the mirror fires (as it would normally) but it won't fire until the release under the selector is fired with a cable release.