I and Dan replaced the bad UL BOSEM unit (SN of bobbin part of that assy is SN250, D0601106-C) with a good one (SN282) pulled out of spare "half-assembled" tip-tilt assy (base plate SN 034).
We also replaced UR one (SN258) with a spare (SN134) that was pulled out of the same half-assembled TT assy simply because we were not sure if the open voltage of SN258 (about 20000 counts) was too small. Later it turns out that 20k counts open voltage is not abnormal.
The newly installed units were of course assembled in the past but without fit check, and it turns out that the gap around the connector was non-existent and I had to loosen some screws and shift things around to make a good gap. I also used aluminum foil shim trick.
After this, we centered BOSEMs for all Tip-tilts to half the open voltage.
| UL | LL | UR | LR | |
| OM1 | -16k | -12k | -16k | -13k |
| OM2 | -11k | -11.5k | -15.5k | -16k |
| OM3 | -16k | -14k | -16k | -11.5k |
WFS DC, AS_C QPD, OMCR QPDs, OMC QPDs and OMC DCPDs all responded to flash light.
Beam diverters moved back and forth.
Picomotors moved. On cable #234, the first, the second and the third channels correspond to WFSA, WFSB and AS_C picomotors. On cable #235, the first channel is the downstream 2" mirror for the QPD sled, the second the upstream 1" steering.
Checked ground loops from outside the chamber, and all cables including SUS were good except beam diverters (we know that they ground inside the chamber) and OMC QPDs (shield grounted to the DCPD signal ground) and OMC PZTs (same as OMC QPDs).
OMC PZT cable shielding also is grounded to DCPD signal ground.
Same as OMC QPDs. It's not clear from D1300376 (OMC PZT cable document) but there seems to be continuity from the shield to the mighty mouse connector shell, which is mounted on the aluminum bracket on the OMC.
LLO alog explaining these: https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=10121
As of now, ISI is locked. OMC is free.
Beam diverter cable sheild needs to be cut at the rack or at the chamber.
With the cables disconnected from the remote rack Beckhoff motor driver module, there's continuity between the cable shell and the rack. Relevant cables are cable #316 and #317.
PZT capacitance:
From the outside of the chamber, used a short DB25 and a break out board to check that PZT pins are not short circuited to stupid things. Since I was able to, I also measured the capacitance.
Pin1-14: 474nF.
Pin2-15: 428nF.
These of course include the in-vac cables and short DB25 cable I used outside.
Sounds the correct range for the PZTs. (spec: 470nF)
Correction: Corey found that the S/N of the pulled and newly put in BOSEMs are swapped in the above entry.
Bad BOSEM that has one PD pin grounded to the coil bobbin part is SN282.