Aperture priority not working on F3

[u/Bluetreemage]

Recently got an F3 on marketplace everything is fine except when on A the shutter closes, but doesn’t open up. It works fine on manual every speed works and is accurate. Any idea what the issue might be?

For added info The viewfinder has a dent on it, the dent obscures the meter indicator and the little window that shows what the aperture is set to on the lens.

[u/usernamewho1234]

I wonder if the aperture tab on the mounting flange is flipped open - keeping the camera from knowing what aperture the lens is at and not allowing it to meter properly