J. Kissel, K. Kawabe, R. McCarthy, A. Pele

At ~11:30a PDT (~18:30 UTC) I began trying to drive the H1 SUS ETMX ESD in Pitch, to replicate a driven, optical lever ASD (e.g. LLO aLOG 12512). To my dismay, I found no coherence. We performed several other excitation tests, including repeating Keita's measurement from yesterday (LHO aLOG 11872), also to no avail. Finally, after obtaining Richard who was valiantly battling the ESD at EY, he told us to check out the monitor read-backs, 
H1:IOP-SUS_EX_MADC1_EPICS_CH0 - 5
which can be found from the A1 (the second ADC ) screen off of the H1SUSEX IOP GDS_TP screen. These channels showed values frozen at ~2050 [ct], which (though spurious) would correspond to a voltage of 
2050 [ct_ADC] * 40/2^16 [V_MON/ct_ADC] * 40 [V_ESD/V_MON] =  50 [V_ESD]
Richard immediately recognized these values as indicative of a failure of the driver.

I started my drive at 18:32 UTC (11:32 PDT), and the bias channel falls from ~30000 [ct] (ADC), to 2050 [ct] at 18:20 UTC (11:20 PDT).

There was activity in the XVEA (between 9:30a PDT - 11:30a PDT), around the racks that the ESD driver is installed, but it was with seemingly unrelated network cabling. So it appears as though the failure was a result of some closeout activity.

However, when Richard and I drove down to investigate,we found that even the driver's +/-18V LEDs were off. After a quick investigation, including a full high-voltage power cycle, with limited tools, Richard concluded that the ESD Driver needs to be swapped with its spare, and is doing so now with Fil. 

Welp -- we got *one* promising night of ALS DIFF locking under 1 [nm] rms...