At $200 a pop, I second the recommendation to measure the voltages on each of the pins on the connectors before frying another node board. I think there are nine molex connectors on the node boards, with about 58 pins across those connectors (if all are in use). Leave the node board out, and then using the schematic, check each pin for voltage. I suspect you will see one pin amiss and can then track that wire down to see where the voltage is coming from.