When you receive boards are sure to double and triple check the contacts and pads for bridging before you solder your pins on and after. The picture is of two pololu's that i bought for making a reprap three worked fine and the fourth shorted out and caught fire. They were all run through the same test on the same board receiving signal from my cupcake CNC and they were all plugged in to the driver carrier correctly. Check all of your boards before you turn them on no matter who you get them from. If you do not have a smoke detector in your workshop get one!