I recently purchased a used Minolta SRT 201 off of eBay, and it has a problem with the mirror locking up. Whenever a use the lever to advance the film, the mirror raises up so that I cannot see anything through the viewfinder. It resets after a press the shutter button but will get stuck again after advancing the film. Has anyone else had this issue and know of a potential fix? I know that I may need to send it off for repair but wanted to see if there was something obvious that I was missing before I do that.