ZM1 in-chamber cable between the feed through and the cable bracket on HAM6 was swapped, loop gone.
It was swapped and the ground loop of that part was fixed. But the new cable didn't have screws in DB25 to secure the connection, so we're transplanting the screws from the old cable to the new one.
ZM1 DB25-micro DB9 cable (that goes to the BOSEMs), disconnecting/reseating/shimming/tilting done, loop gone.
There was also some problem(s?) with ZM1 DB25 to micro DB9 cable. It's the same failure as the one reported for OM3 yesterday (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=41709). Jim tried to angle the connectors to clear the problem, which helped three of them but LR was persistent. He half-disconnected the micro DB such that no metal part of the back shell could possibly touch the aluminum BOSEM body/plate but there's still electrical connections to the pins, and the problem still persisted, which sounded like a problem of BOSEM itself. However, when we totally pulled the BOSEM from the TT cage and connected it back to the cable, we didn't see ground loop.
I inspected it and saw a tell-tale tiny gap between the back shell and the BOSEM/plate. As a preventative measure we performed foil-shimming-shell-tilting procedure explained in https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=12346. First attachment shows "after" photo (there's no "before"), there are three potential short circuit points, two (circled in yellow) look much better, one (red) is actually better than before but I can only barely slip a sheet of foil through. The second attachment shows the foil used as a shim underneath the micro DB9 on the BOSEM body. It's really important that the cable side connector doesn't sit on this foil. The third one is an in-situ picture. Looks scary close but actually there's a gap. Suboptimal but this is as much as we can do.
OMC QPDs is left as is, nothing to fix.
After going back and forth between Koji and Rich, I'm convinced that this is a known symptom.
Ground loop checks were completed after in chamber cabling work.
SUS checked out good with the exception of OM3 (ISC_238).
ASC WFS cabling (ISC_255 & ISC_266) at rack side (DB15 connector) does not have pin 8 connected to shield. Shield tied to both pins 14 and 15.
Beam diverter cables (ISC_316 & ISC_317) at rack side (DB9) don't have pin 5 installed. Shield is tied to earth ground.
PZT cabling at rack side (ISC_409) does not have shield and pin 13 tied together.
See entry above from Keita regarding OMC QPDs.
OM3 problem comes back, fixed by cable routing and PEEK tubings, (Fil, Ed, Corey, TVo, Keita)
Fil reported that OM3 problem was back. It was really inconsistent, the only thing that was consistent was that when we remove DB25 cable at the OM3 bracket and lift it up from the table the short circuit is gone.
The biggest problem was that the DB25 cable was going from the OM3 bracket to the fast shutter and was pressed against the fast shutter body. The corner of the fast shutter body ate into the mesh of the DB25 cable and contacted the shielding. Each time we touch that part of the cable the resistivity of the short circuit changed from zero to open and anywhere in-between. That this was new to us makes sense because we've moved OM3 and FS after O2.
I installed a new cable clamp to pull the cable away from the fast shutter to reduce the pressure (the FS-OM3 distance is so short I was worried about making a kink at the connector if I try to completely pull the cable away from FS) and put a short PEEK tubing that is a leftover from TMS cable insulation (first attachment).
We also observed that wiggling the micro DB cable sometimes changed open/short, and it wasn't clear if this was due to me accidentally touching/affecting DB25 cable or if there's another short circuit path via cable shield. I installed another PEEK tubing to UR coil micro DB cable where it was bending at the edge of the OM3 cage (second attachment, red arrow points the tubing).
After these OM3 was consistently clear of the ground loop.
As a side note, we removed LR coil because I thought (in error) at some point that LR BOSEM was suspect. We put it back in, and measured open counts (20460 or so) and set the depth such that the input becomes half of the open number. We also adjusted LL depth but didn't touch UR and UL as they looked good.
ISI was unlocked
After removing all tools from the ISI table, ISI was unlocked by Corey.
No need for ground loop test again
We didn't touch any of the cables except OM3, so no need to test ground loop again.
In ICS, I've removed the cable (D1000225/S1106893 & gave it a Defect record), which was suspected for causing part of the ground loop for ZM1, from the HAM6 Top Level Assy load & added the new cable (D1000225/S1100410) to the HAM6 sub-assy-load: D1300122.
Note: In D1300122, a D1700316 cable is called out here instead of D1000225. Are these interchangeable?
[Confirmed w/ Hugh that he installed the regular D1000225s because we had limited supply of the D1700316 & they were used for VOPO. Richard M. told Hugh the standard D1000225s were acceptable for the ZM1 suspension.]