Ryan had a hard time locking the OMC, and there was no DCPD_SUM spikes as Ryan moved the PZT offset manually. We saw nothing in the OMC trans camera either.

I found that the OMC PZT2 monitor dropped to zero-ish at 14:23 PDT (21:23 UTC). That coincides with vacuum-related activity for HAM1, not sure if they are related.

In the mezzanine I found that the output of the HV driver was zero.

Pressing VSET and ISET, I saw that the driver was set up to 110V 80mA. Pressing RECALL -> ENTER didn't do anything. I also noticed at this point that the unit was somehow in CC (constant current ) mode, which is usually automatically determined by the power supply. It should be in CV mode.

I turned the output off, asked Ryan to turn the PZT offset to zero (which means the middle of 0-100V range, i.e. 50V, so I should have asked -50V offset), power cycled the unit just because, pressed VSET again (it was still 110V), pressed ENTER, turned the output ON, and it started working again.

Ryan moved the PZT offset and the HV monitor responded. Shortly after this the IFO lost lock but I don't think that was related to the HV.