Rob will deal with this directly, but we've had one mk2 with a bad ram chip; the RAM is a different brand to the stuff in the Mk1, but this shouldn't be a problem.

To perform a ram test, wait until the unit falls over (the other unit had a heat-related fault in the chip) then power cycle it and press Ctrl-T at the bootup prompt - it then goes through a basic hardware test. Do this a few times and note any errors.

Hugo