[br]
On my Mini 9 it appears to me that the iris sometimes gets misaligned when you rotate the exposure wheel (the wheel at the front of the lens with a notch that lines up with icons for indoor, cloudy weather, sunny weather, etc. .) to adjust for the light conditions. The random misalignment of the iris in the lense may explain why you will have properly exposed photos and then the next ones you take are all black. Unfortunately, I dont think there is any real fix to this if you're not handy with disassembly and repair. It is just poor build quality.