For some weeks I use my Raspberry Pi as kind of a surveilance system. It worked quite well but after some days it stopped working. At first sight the source of trouble seemed to be the wireless lan interface connected to the USB port. So I searched in the internet for a while and came across the
smsc95xx.turbo mode=n setting in the
/boot/cmdline.txt file. Much better then but still not perfect. After two weeks it stopped again and this time it didn't want to come alive. Well, it came alive but only for a short time until I tried to download a file via wireless interface. The terminal only showed many warnings like
journal commit I/O error and that's all from that moment on.
After some internet seach I found this page where they explained how to check the voltage.
5.07 V showed mine. Looked perfect. Then I booted to device while I was measuring and then the voltage dropped to 4.6V a few times. Multimeters are kind of slow so it must have been a huge drop. Needless to say that I used a quality power supply from Apple. Seems to be the root cause for my problems.
I'm going to order a new power supply right now...