Since yesterday, we have received an answer from Ali and Keita, that the determination is that the cathode and anode pins are in the correct location. There is a longer explanation about what's going on here and which diagrams are wrong, but I will leave that to them. Therefore, the only cable work that needs to be done is to adjust the pins on our "bad" cable, and then switch the DCPD cables between OMCA and OMCB.
Morning (no cable work):
Oli and I pulled the first contact that we left from yesterday. We just need one 50/50 45 deg AOI mirror for BHSS, and we were able to completely clean two of this type. More of these mirrors will be needed for the greater BHD layout, so Oli and I need to revisit the other three that still are not clean. For now, they are stored on the flow bench in clean single cases.
We went to begin the BHSS alignment, and found that no laser beam was coming out of the fiber. Some time between this alog, when Camilla and Oli aligned the beam into the fiber, and now, the beam was misaligned again. We think one of the mirrors to the fiber coupler was bumped. Correcting this took a little while. Oli had to leave, so Keita and I continued with the alignment. Luckily, our downstream alignment is still good- with the iris alignment template placed on the BHSS, we can see the beam comes down the center of both irises to OMCA.
Most of the beam reflects off the OMC, so Keita and I started turning up the power into the fiber. At some point, we turned up to 20 mW coming out of the fiber. We could see a faint beam transmit from the input coupler and make it to the output coupler. However, we still had a hard time seeing any beam make it to the DCPDs, probably because the power is still very low. We set up a beam block of the OMC REFL path for now, since it just goes right back off the suspension. At this point, we realized it's probably not a good idea to put so much power into the fiber, so we lowered the power again to have about 2 mW coming out of the fiber.
Afternoon (cable work):
Keita and I proceeded to fix the cables. We first checked which cables went to which pins:
Cable D2300119 (for OMCB): longer is on trans PD, goes to pins 4/5, shorter on refl PD, goes to pins 1/2
Cable D2300118 (for OMCA): longer is on trans PD, goes to pins 1/2, shorter is on refl PD, goes to pins 4/5
We confirmed that this is the correct wiring according to D2200276
Keita opened up cable D2300119, as this is the cable with incorrect wiring- case was wired to pin 2 and pin 5 instead of pin 6 and 9
We confirmed that the cathode is correctly wired to pins 1 and 4, so we only needed to swap 2/6 and 5/9.
Keita proceeded to switch the pins (this is a very short sentence to describe a long and painful process of removing various peek parts, poking pins through holes and resetting all the peek parts once finished)
Keita reclamped the lower part of the wires and we decided that we should clamp it very tight, as there were no gaps in the clamp on the other cable.
We then swapped the cables, as 118 was incorrectly placed on OMCB and 119 on OMCA. We decided to unscrew the PCB assembly on the back of each tombstone, and then swapped cables, paying attention to which cable went to trans and refl. Note: plugging the PCB assembly back into the DCPD pins is much much easier than inserting the DCPDs from the front.
We then decided to confirm the wiring was correct so we:
- checked that the case of each PD was wired to pins 6 and 9 (pass)
- checked the diode polarity was correct betweens pins1/2 and 4/5 (pass)
- checked that there were no shorts between any of the pins in the cable (failed for cable 119)
We found a short between pin 3 and 9 on cable 119. We removed the PCB assembly from the back of the DCPD tombstone and checked again, still a short. Keita then removed the lower part of the dsub9 assembly where the wires are clamped, and there was no longer a short between pin 3 and 9. We found one wire that was a bit stripped (see photo), but this was the wire for pin 4, so that didn't explain the problem. We were not able to find anything that could cause short between pin 3 and 9. We decided that maybe the pressure of the clamp caused this problem, so Keita reclamped the wires but less tightly, no more short. We checked one more time for case wiring, polarity, and shorts and all tests passed. Done!
