Bought a package of cameras described as nonfunctioning. Gambling you know. A Hi-Matic E works and I thought at first sight this black ST901 does the same.
On second sight it doesn't.
It works just fine in auto mode, shutter speeds seem accurate.
But when changing to manual the shutter doesn't open. Advance is working, the mirror slaps but the shutter stays closed. It seems the first curtain is coupled with the second and just drags it with it. This doesn't happen in auto mode. I thought at least 1/60s and B are purely mechanical.

Any ideas how to fix this, besides using the camera just in aperture priority AE mode?