We naively hoped that just replacing the fuses would fix the problem with the PZT HV drivers. Alas, this was not the case.
All of our investigations (other than visual inspections) today have been of the PZT2 module. We have not applied any electricity to any PZT1 components/modules today.
After blowing a few more fuses (not good, we know, but we really didn't know what was going on at the time and were convinced that our changes between fuse installations should prevent fuse-blowing, including removing all modules except the HV driver), we found that the YAW driver for both PZT1 and PZT2 has severe discoloration on the PCB, and several resistors and other solder joints are damaged near some high voltage regulators. Pitch on PZT1 looks a tiny bit discolored, but doesn't look totally cooked like the 2 YAW modules do. So, at least PZT1's Yaw was cooked before we started replacing fuses, since we haven't plugged it in yet today.
We then began some more methodical checks:
We bypassed the fuses by applying 10 Vpp = ~7.2 Vrms to the input side of the big transformer on the PZT2 HV driver board. (This usually sees the 120 Vrms from the wall AC, so we were looking at things with a factor ~16 attenuation from what they normally see.) We then measured things on the other side of the transformer, and made sure that they made some sense (one path for 5V stuff, one path for 15V stuff, one path for 180V stuff). One of the rectifying diode bridges (the one for HV) didn't seem to be working, and didn't seem to have all of its pins connected, as if perhaps one or more diodes inside was destroyed.
When I went home for dinner, Koji continued looking at the low voltage supply capability of the PZT2 driver. He removed the diode bridge from the HV path, and also removed the FET that lives on the output side of the HV driver board. He was then able to energize the HV driver and the non-burnt pitch module. So the +\-5 V and +\-15 V paths have been confirmed okay for PZT2's driver stuff.
What I will do tomorrow (when there is someone here to rescue me if I crispy-fry myself) is solder a wire to the now open pin of the backplane connector on the HV driver board, so that we can supply an external 180V to the pitch / yaw modules (although, obviously we won't be using the burnt yaw modules as-is). Tomorrow I'll start by applying a nice small voltage, check that things still look okay, no shorts, and then I'll slowly increase the voltage until I get to the nominal 180V.
Since the low voltage stuff on the driver board is working, once we supply an external 180V (if successful), we should be able to re-install the PZT driver and drive PZT2.
Since both Yaw modules that we have are burnt, I am proposing that we use the PZT2 HV board (which has been checked and modified this evening) with the 2 pitch modules. Since we are not actively utilizing the strain gauge sensors, the fact that the calibrations on these modules are not exactly the same (rather, that PZT1's pitch is not the same as PZT2's yaw) should not matter at all. This means that we will not be able to energize PZT1 at all, but that shouldn't be a problem. Even when PZT 2 was working, PZT1 had very, very, very limited motion through the full range of applied voltage, so having no driver connected shouldn't have an impact.