Following up on Keita and Koji's converation, Sheila and I took a closer look at the OMCR DCPD in HAM6 to see if there are any cracks. We could not positively identify anything resembling a crack on the DCPD (images attached). We could also not see where the DCPD was hole punched. What is the typical size and placement for these holes? More images here. The DCPD is definitely quite dirty. We compared against some DCPDs of a similar design in HAM7 and can confirm that the OMCR DCPD is visibly much dirtier than those.
We also inspected the OMCR shroud input aperture for signs of pitting and other damage. There is no damage to report. We spent some time looking at the output aperture because we saw some potential damage along the aperture edge. After taking photos at various different angles to rule out reflections, we determined that apertures are fine, save for the occasional speckle on the shroud and the rouge edges likely left behind by the machining process. Images attached. More images here.
Today I took pictures and it really seems that the glass was cracked.
1st attachment is a cellphone picture, you can see something at the right edge. That thing never goes away regardless of your eye position and lighting.
2nd is a close up view from the side using a dedicated camera.
It seems to me that the front and the back surface of the glass each developed a scallop-shaped crack. I couldn't picture the hole in the can, not sure if this was actually punched or not, but I think the cracks are real.
You cannot see anything like this on the left edge of the PD (3rd attachment).
Sheila noticed that the two dots inside the PD can where the PD cables attach on this PD are vertically aligned. In the HAM7 SQZ PDs the dots are horizontal, e.g G:PD1, H:PD1, F:PD1. Is this fine?
Hi Camilla,
Not 100% certain that I know what you mean by "dots." I am assuming you are referring to the leads that penetrate the diode can. Either way, these are not quadrant photodiodes, so the rotational alignment of the photodetector element should not matter. It could be that you are comparing this device to other devices that use different models of photodiode, but again, the rotation of a single element diode will not matter.
Spare PD looks similar.
During installation I thought that we didn't have a spare OMCR DCPD, I somehow mis-remembered that everything we didn't use was sent to LLO but that wasn't true. So I took pictures of the spare too, and things look about the same.
1st picture was shot with a cellphone and an LED flashlight. It's not particularly difficult to take this kind of picture but note that the flashlight should be much brighter than the ambient light, and you should place flashlight as well as the camera such that reflection from the glass/metal/pd won't come into camera's view. You also avoid reflection of bright/white background coming into camera's view. You need to experiment.
2nd and 3rd picture shot with a stand-alone camera and a macro lens show some particulates are closer to the sensor plane (2nd picture) but more are on the glass plate (3rd picture). Cleaning the outer surface didn't change things so I assume these are mostly on the inside surface.
4th and 5th picture show the structure that looks similar to what we observed for the one in HAM6. Again this might be crack, but an alternative explanation that came to my mind is that a hole was successfully punched, which made protrusion of jagged metal edge of the hole into the can, and we're seeing that through a non-flat glass (it's apparent that the glass is not particularly flat around the edge, look at the last picture).
For inventory purpose:
| PD-cable-enclosure assy |
Component: PD-cable |
Component: enclosure | Status |
| D2100381-V2-S2200257 | D1600079-V3-SN1 | Spare | |
| D2100381-V2-S2200258 | D1600079-V3-SN2 | WHAM6 |
(I'm 100% sure which component is in WHAM6. I couldn't find any record of which PD-cable-enclosure assy comprises which component, I just assume that younger components belong to younger assy.)
