Ground loop checks for HAM1 and HAM6 are now complete. Not all issues were addressed either to limited access to chamber feedthroughs and cabling.
HAM1:
RM2 (Cable label ISC-229) Pin 13 shorted to ground
HAM6:
ZM1 (Cable label SUS_SQZ-20) Pin 2 shorted to ground
VOPO (Cable label SUS_SQZ-2) Pin 13 shorted to ground
F. Clara, C. Gray, K. Kawabe, R. McCarthy, M. Pirello, H. Radkins
Below is a list of what was fixed and what was not fixed.
Fixed 1: Good old "DB25 in-vac connector screws too tight or too loose" problem for RM2, LSC-REFL_A DC and ASC-REFL_B DC.
The problem is detailed in alog 12348 but I repeat it here.
When four screws that put the connector shell together are not tight and thus proud of the mating surface, or if the two screws that attaches the connector to the feed through are too tight, one or more of four screws touch the metal surface around the feed through, thus short circuiting the chamber and the cable shielding.
Tell tale sign of this is that the impedance between pin13 (from outside of the chamber) to the chamber is only a few Ohm. If you have a problem at the sensor side, the impedance tends to be larger, e.g. after we fixed this for ASC-REFL_B but ASC-REFL_B still had the dog clamp problem (see below), the impedance was about 30 Ohm.
As you loosen two in-chamber screws that attach the connector to the feed through, the impedance immediately starts to increase. To "fix" this specific problem, you completely remove the in-vac connector from the feed through, tighten four screws that put the connector shell together, reattach the connector to the feed through but don't really tighten them with any serious torque. Even then, when you rock the connector back and forth, the problem might come back.
This seems to be a huge repeating problem so we need a fix for future. How about using a thin PEEK spacer that covers the four screws?
Fixed 2: Dog clamp short-circuits the main body of ASC-REFL_B to the chamber.
Some people don't know that ALL ISC in-vac detectors are insulated from the base plate and thus from the table surface.
Dog clamps could be used to fix the base plate, but if you do that you need to be really careful not to touch the main body of the ISC detectors, or the main body (which is connected to the circuit ground) is short-circuited to the chamber.
Corey and Hugh slid the dog clamps away from ASC-REFL_B and the remaining 30-something Ohm went to completely open.
Though ASC-REFL_A didn't show short circuit, since one of the dogs looked close it was also moved.
Not Fixed: RM2 shield to chamber short circuit problem which is probably on the TT side, not the feed through side.
After fixing feed through screw problem for RM2, the impedance went up from 1.6 to 30-something Ohm, indicating that this is something far away from the feed through. I and Daniel decided NOT to spend hours to identify and fix this as this could be something like a reincarnation of alog 41722 which was a reincarnation of alog 12345.