I have been using my M6 for a number of years without problems. I get the whole kit tested by a mamiya technician fairly regularly as a free service from one of the local photography exhibitions in MN. Anyway, the problem started earlier this winter, and I attributed it to potentially cold batteries, and it went away when the batteries were warmed up in my pocket for a while. Unfortunately, yesterday, the problem came back. The batteries aren't brand new, but are not old, or out of juice either.
When pressing the shutter, the shutter opens, and appears to stay open. I quickly put on the lens cap during this time, and stopped the lens down to avoid anymore fogging than the one frame. I powered off the camera, and removed batteries, and put them back in. Switched it back on and the meter appeareed to work, but I could not wind it on as the shutter was still open!!
Eventually, the shutter closed, and I was able to wind it on and close the film blind. I swapped lenses and then the camera worked as normal afterwards. I swapped back to my original lens, and again things were back to normal Could this be a battery problem, or is there something else going on that I need to be aware of? Could there be a bad contact somewhere? I can remember in the cold MN winters when temps got down to -15 both my 75mm, and 50mm lenses shutters did this.