Isolated the linear very reg, short was still there. Figured it was the capacitor. Un soldered it. Short was still there. Re melted positive pad - short gone. Re melted the re melt and pulled the solder around ... short came back. So somewhere very close to the positive pad a trace has lost its protective coating. This is what you get with (over) used parts.
Solution: I should replace the pdb ... but I'm not going to. I re soldered the vreg, found another ceramic cap and soldered it back in. Then re attached power and ground from 5v to fc. I checked for shorts along the way and readings look good now. It should be fine - time to get a deans on there and test with a battery (and smoke stopper).
Update: no smoke. Back to the building.