There is a silver retaining ring under the rewind knob that holds down the main switch. While it's possible that it is loose and may only need tightening, in almost every X series Minolta that has come into the shop with this issue, the plastic rewind shaft bearing assembly that the retaining ring attaches to is cracked and needs to be replaced. This means removing the top cover, lifting the rewind side circuit board, and installing a new rewind bushing. There is also a ball bearing and spring that provides a detent for the main switch and these often get lost when the switch comes loose. Without the main switch operating, the shutter will not release.
Bill
