Wade noticed that aux2/3 pedestals were small and negative. I checked with a voltmeter and found no power at the preamp input. Moved that power cable to another channel on the preamp power distribution box, those pedestals now are ~100 mV as usual.
I think this is the third blown fuse in the preamp power distribution panel. All have involved the aux2/3 preamp, but the previous two involved a tee'd power cable. I may even have swapped that "suspect" preamp out. Will watch and see.