[daltore]

We had the same problem with one of ours. It was a result of Backwards Power Man (a member of our team connected cables to a battery backward and plugged it into our router, which fried a 0 ohm resistor, thus he is now Backwards Power Man). Well, he struck again by plugging the battery into the M terminals of the Spike and it started doing the same thing. However, this was only for a couple of seconds. If you have a relatively large motor or one that is often backdriven connected to your Spike, or you reverse direction a lot, you may be feeding an inverse current into your Spike, thereby killing the relays.

Another possibility is that you may be drawing more than 20 amps with your motor. The one-time fuse in the Spike is slower-acting than the auto-reset fuse on the PD board (which is a good thing), and so if you draw more than 20 amps of current, the auto-reset fuse will trip first, and cut power to your Spike. Remember, the multimeter is your friend.