I'm having a similar problem and also wrote a mail to farnell already...
Here's what I wrote to explain my problem and I just wanted to ask you guys if you have an idea what else I could try...I do not have a multimeter or infrared thermometer...
I finally received my Pi and of course I was very excited working with it.
But here is my problem:
The Pi regularly turns off suddenly, without the system shutting down or any premonition.
The time of the turning off varies, sometimes right after startup (for example when logging in), sometimes after having started the graphics server and installing something in the terminal etc. So it has nothing to do with what I'm doing with the Pi. It's even turning off when I do only have the Display connected (and of course a SD-card mounted) and I'm waiting a little.
I'm pretty shure it isn't the SD-card either, because I tried 2 different cards. The second one is a Mustang 8gb SDHC Class 10, which is in the Wiki-List of working SD-cards:
http://elinux.org/RPi_VerifiedPeriphera ... g_SD_Cards
To ensure it's not the HDMI-output, I also connected via the RCA-Video out.
I also tried different power solutions.
I plugged the Pi in my Motorola Smartphone charger, which should bring 850mA.
I plugged it in a powered USB-Hub, which didn't work either.
I tried the "always-on" Usb-Port of my Lenovo Thinkpad, which should bring 1000mA.
I tried powering it with a Y-Cable, combining all of the above.
I read the forum posts, but couldn't find a solution.
Can you help me? Or is my Pi broken?
I'm using the Debian Image from the Raspberry Pi Homepage. (19-04-2012).