J. Kissel, B. Weaver, S. Dwyer, D. Sellers, G. Traylor, T. Hardwick

I'm writing down some of the ideas we've had on what might have mechanically changed with the QUADs to cause the symptoms that we see.

(1) PUM Flags have gotten bumped.
	- This could explain some of the discrepancy between optical levers and the PUM stage OSEMs. (LHO aLOG 37799)
	- This might also explain why some of the violin mode damping coupling has changed. (LHO aLOG 37507)
	- This could not explain why we need more torque at the top mass to make the test mass realigned. (LHO aLOG 37799)
	- As long as they’re not rubbing, this wouldn't show up in top-to-top transfer functions. (LHO aLOG 37689)
(2) The pitch adjusters on the UIM / TOP mass have moved, creating a new static “DC” pitch alignment.
	- A small move in these pitch adjusters can cause misalignments at this level (~100 urad) of pitch change.
	- This could explain a relative misalignment that is described by what we see in the OSEM vs. Optical Lever story.
	- This could explain why we need more torque at the top mass to move the test mass back to the optical lever positions.
	- This could not explain why some of the violin mode coupling has changed.
	- They have not caused any new rubbing, this would not show up in the top-to-top transfer functions.
	- This may show up in top-to-top mass transfer functions as a shift in frequency of some modes due to the moment of inertia change.
(3) The UIM to PUM suspension wires have slipped slightly in there prisms
	- This would explain a relative misalignment that is described by what we see in the OSEM vs. Optical Lever story.
	- This could explain why some of the violin mode coupling has changed.
	- This could explain a relative misalignment that is described by what we see in the OSEM vs. Optical Lever story.
	- This should show up as a change in resonance frequencies in top-to-top TFs, in especially the rotational DOFS.
(4) Some EQ stops are now rubbing.
	- The top-to-top mass transfer functions essentially rule this out. ETMX and ITMY TF have some niggling features, we'll go back to it for more precise measurements.
(5) Optical levers are untrustworthy because they have moved.
	- We’ve ruled this out because restoring optics to their optical lever values after the EQ have made the interferometer go, and we’ve checked spot positions on optics once the IFO is going and they’re in the same place as before.


More ideas / comments / questions welcome!