Yesterday, we discovered a short to ground from the +5V power to the electronics in FPP C2. Today was spent on an exhaustive search of the short.
Part of difficulty with isolating this short is that fact that a single +5V supply powers both U and V planes, which are on opposite sides of the chambers. At Brad's suggestion, we broke the connection between the two planes and found that the short is on the lower plane (V?).
Bad news: this is the side that we can see, and there is no obvious short. The busses are clearly separated, and there is no contact between busses through the lugs. We also tried canned air in the hope of moving any debris that might be causing a short, but a short still exists.
Good news: this is the side that we can access, so it is feasible to disconnect every wire from the bus, check for a ground between busses, and reconnect every wire. This will be done tomorrow. We should be able to have both low and high voltage connected tomorrow evening.