Sanguinololu Mosfet burn out

[tigerx]

So i just bought a Geeetech i3 Pro B and finally finished building it, only to do a test run on the heaters to check if they were working, the extruder worked a charm however the heat bead( MK2a) i was heating to 50 degrees, at about 45 the mosfet started smoking... so disconnected, and now the mosfet just constantly supplies current, and everytime i connect the heat bed same thing. I've done some reasearch and its because my heat bed has only .8ohms resistance and not 1.3-2ohms causing nearly 15.5 amps to run through the mosfet hence burning out. Now i bought it on ebay, and have requested to have the Sanguinololu board and the heat bed replaced ( the seller just imports them... so hopefully he says yes, others wise i have to pull it all apart and send it back). Now question is, when/ if i get an new board and heat bed, how do i stop this from happening, in case the heat bed still has low resistance around the 1 ohm mark?

I'm only new to 3d printers, and really want to get this working, i have had a few other issues related to firmware, and getting it to work on mac and also arduino but i'm slowly getting there...
if someone could please help!

[Mark]

http://www.geeetech.com/forum/viewtopic ... 13&t=17039
you can refer to the post here, check if pin2 and pin3 of your hotbed are connected or not.
And the way to install the firmware is here:
http://www.geeetech.com/forum/viewtopic ... 20&t=16433