Can't set shutter speed past 250

I recently got a Revue labelled Fed 4 that seems to be working smoothly aside from one strange problem. When I change the shutter speed from 250 and then take a shot I can't return to 500, the shutter speed dial will only let me select from 250 down to 1. If I take a shot on 1 the shutter fires quickly and then I can rotate the dial all the way around and back to 500. Has anyone seen this kind of behavior before?

Hello
Is shutter remains open when you are using B setting?

Hi, its possible the shutter speed knob has been replaced incorrectly. Wind the shutter and make sure that the index mark on the speed knob rotates clockwise as far as 1/30th. If it won't, then try to rotate it anti-clockwise past 1 second. Do not force it. Should this be the case then you need to loosen the grub screw and reset the position of the index marker against 1 second, then check it will now move back to indicate 1/30th.
However if there is no issue with the shutter speed knob then it sounds like something is wrong under the top cover with the speed selection mechanism