I have a minolta x-300 and the shutter won...

'B' settings and other long exposure settings on electronically controlled shutters are always the death knell for a nearly exhausted battery. The X-300 is totally reliant on batteries to power the shutter and so the shutter lock-up is cured simply by replacing the batteries with fresh ones. For consistently accurate exposures use two silver oxide SR44 cells instead of cheaper lithium alkaline LR44 cells which have an unstable voltage.

Don't leave it too long though as the shutter can stick if left this way for too long.

A pdf manual for your camera is at the following address:-

sawlani.googlepages.com/minolta-x-300.pdf