On Tue, Sep 13, 2011 at 8:16 PM, Brent Brown wro= te: > What I strongly suspect is happening is that plugging into header pins th= e GND pins > are not contacting first (there is nothing to guarantee the order of conn= ections) and > when +12V pin contacts is couples power through discharged elelctrloytic = caps on > daughter board to GND rail, then "backfeeds" to +3.3V rail through intern= al body > diodes of chips on that rail, pushing up the +3.3V rail and popping the p= rocessor on > the main board. Similar could be happening on RXD, TXD and +5V rail... bu= t nature > of 2 failures so far suggest +3.3V rail more likely. Ok, I'm definitely not an expert in this area, but would a diode on the 3.3V line in between the connector and the rest of the circuit on the daughterboard help? Josh --=20 A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. =A0 =A0 =A0 =A0 -Douglas Adams --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .