I think the reason I did not have trouble before might have something to do with a misconception I had about the breaker switches.  For some reason, I thought you had to lock them in the up position.  If you click on them and move the mouse, they stay in the up position.

So, I used to have all of the bus tie, generator, and field switches locked up along with the field and generator switches for the APU.  I guess that prevents the APU from actually tripping.  (I wonder what that would do to the electrical system in a real 727.)

Anyway, I can't find any reliable way to keep the CIVA units from dying without doing that.

I tried switching to standby power, then connecting the engine generators, then switching to an engine generator for power.  No go.

I already had the ground electric tweak in effect because the avionics used to die during taxi, so that apparently doesn't help.

Oh well.  I finished a 22-leg, around-the-world tour tonight.  I guess I will just fly old-school from now on since I actually have charts for the US and don't really need the CIVA any more.