Randy moved the 3IFO ISS PD array (S1202968) crate from MY storage to the OSB yesterday (WP). I opened the crate, moved the transport/storage container to the vacuum lab and optics lab to inspect. It was in a good shape except that some upgrade parts weren't there. Since I'm already forgetting what happened to other units, here's the summary.

First about parts.

• 3 of 4 units require replacement of the new PD array plate (D1300322), but we (are supposed to) have parts. I'm not sure which units were meant to be ready for installation, but if we replace the PD array plate, realignment must be done.
• None had the QPD tilt but we have enough parts for this.
• 1 of 4 units had the low QPD, i.e. QPD plane is much closer to the PSL than array PDs. No parts were located for this, and mostly for this reason we'll have to live with just two spares for 3 instruments instead of 1 spare per each instrument.
• Blue glass beam dump plates were only found for two units. The remaining two don't have these. This might be OK, the optics are easy to transplant when we pull the in-chamber unit.

Next, the summary per unit.

• Good spare S1202965 already has all upgrades. It's the only one with an updated PD array plate already installed upon initial inspection. Also see alog 83077.
• Second apare S1202966 will be OK (PD array plate will be replaced, QPD will be tilted, will use parts from the damaged unit of parts from the damaged unit S1202967 for some other things) except that blue glass beam dump optics aren't found. Also see alog 85019.
• 3IFO S1202968 will be OK (PD array plate will be replaced, QPD will be tilted).
• Damaged spare S1202967 cannot be restored in short order as that would mean locating or making/procuring new parts to make QPD higher (because the dirty parts from this unit will be reused for the second spare), C&B all new and existing metal parts, cleaning and reinstalling all optics, inspecting the surface of all 8 PDs to find particulates AND realigning the entire unit, which will be extremely time and labor intensive. Because of this, we'll only have 2 spares for three IFOs (H1, L1 and 3IFO) at least for now. Also see 82731.

Here's the thing about the PD array plate D1300322 (see attached). The updated version has a wider 100deg conical bore for larger beam clearance because it was found at some point (ECR E1400231) that the clearance was too small for the original bore and the reflection of some PDs will hit the bore wall at an glazing angle instead of hitting the beam dump. It's also easy to imagine that if you fiddle with the alignment for the production unit in chamber, INPUT light on some PDs will hit the bore wall first before hitting the PD surface.