Following up on the possible damage to the common path daughter board, it appears that there is an issue. This board, DCC-D040424, buffers and then provides some amplification if one chooses to solder some resisters and capacitors in. Right now it should be simply buffering but it is railing to a fixed offset in the mixer circuit.  

The north (RCAV) field box was switched out for the south path (ACAV) box (that I know is working correctly) and I found it worked as expected.  I then switch the south box's daughter board into the North (RCAV) field box and it operated as normal. The issue is therefore in the daughter board only.

The mixer op amp circuit uses U1 and U3, neither of these chips have visible damage. U4 was the one with obvious heat damage from the previous short. As it had the most obvious damage, I desoldered U4 and changed it out for another LT1125CSW. This isn't easy as its surface mounted and looks like some kind of machine done job.  I think I did a little damage to the pads, but there is enough left to give a good enough electrical connection.  I need to check with Koji, or someone else with wisdom, what the best soldering iron temperature is for doing this kind of stuff. 

Plugging the daughter board back into the north field box, it appears that the channels associated with U4 are working fine, I will need to maybe replace the other LT1125 and OP27s tomorrow. We kind of need the monitor channels to diagnose issues and also for the PID laser slow controls so this needs to be fixed.

Do we have spares of these boards are they hard to reorder in lots of one?