We previously reported that the wiring to ground on the OMCA DCPD dsub9 cables seemed odd, see 89562. There appears to be two conflicting diagrams of the pin wiring, D2200276 and D2300119. Neither of these diagrams follow the correct pin naming practice either.
Today, Oli and I checked the ground connectivity for the OMCB DCPD dsub9. The case ground is wired to what is labeled pins 6 and 9, according to both of the diagrams above and also proper convention. However, this is different from OMCA, where the case ground is wired to pins 2 and 5 (following the incorrect naming of the diagrams above), or pins 1 and 4 (following correct naming conventions).
So either way, we have two different wiring set ups for OMCA and OMCB. We have only checked the ground pins so far, and it seems like we should confirm the cathode and anode wiring as well.
To summarize:
- we have two different diagrams for pin wiring
- OMCA and OMCB are wired differently from each other
- the diagrams are not following proper pin naming convention which is making this more confusing
Two problems with the drawings.
1. Case grounding.
As for cable and connection drawings, D2200276-v4 wiring diagram specifies that pin1-2 and pin4-5 twisted pairs carry the photocurrent, pin1 and pin4 being cathode, and case grounds are routed to pin6 and pin9, between DCPDs and the in-vac DCPD frontend. See the 1st attachment.
D2300118 DCPD to DB9M cable doesn't agree with the wiring diagram, it routs the case grounds to pin 2 and pin 5. See the 2nd attachment.
D1300369 DB9F-DB9F cable drawing agrees with the wiring diagram in that pin1-2 and pin4-5 are twisted pairs.
D2000592-v3 in-vac DCPD frontend seems to be compatible with the wiring diagram in that it routs the pin6 and 9 to the ground.
So, D2300118 DCPD to DB9M cable drawing is singularly incompatible with others.
Below is a summary table of the above together with reality check of the DCPD-DB9m cable. It seems that there's no way OMCA cable works. Anode/Cathode check wasn't performed (yet).
(outside of the enclosure feedthrough)
Internally routed to
PD1 pin1
Internally routed to
PD1 pin2
Internally routed to
GND
Internally routed to
PD2 pin1
Internally routed to
PD2 pin2
Internally routed to
GND
2. Polarity of the diode seems to be wrong.
Assuming that the wiring diagram and the in-vac DCPD frontend circuit diagram are both correct, cathode1 and anode1 are routed to "PD1 pin1" and "PD1 pin2" while cathode2 and anode2 are routed to "PD2 pin1" and "PD2 pin2". So, pin1 and pin2 inside the frontend chassis are cathode and anode. Again look at the first attachment.
However, whey you look at the circuit diagram of the frontend (3rd attachment), pin2 is connected to the positive bias and pin1 is grounded (via the huge inductor). This means that the PD is forward-biased and will be unusable. Is this only in the drawings?
What to do.
First thing is to check the diode polarity in reality, i.e. if cathode is routed to pin 1 and 4 (which I expect) or to pin 2 and 5 (which I don't expect). In parallel, check with Ali/Dean that my assessment of the polarity makes sense or not.
Depending on the results of the polarity investigation, we'll determine which cable needs to be reterminated how. If we're lucky we'll just reterminate only one cable, but if the PD polarity is indeed wrong we'll have to reterminate all cables.
Here is a further update. This is based on conversations with Keita and Betsy, and emails to and from CIT and LLO.
At first, it appears one issue here is that I have made a mistake OMC placement, as D2200276 indicates that OMCB should have the DCPD cable labeled D2300119 (and PZT cable D2300121), and OMCA should have D2300118 (and PZT cable D2300120), and I installed them opposite according to the DCPD cables. This doesn't account for the wiring issue; it would only make a cable length difference.
Oli and I went into the lab to swap around OMCA and OMCB, and realized that one OMC has the DCPD cable for A (D2300118) and PZT cable for B (D2300121) and vice versa. So it's not clear which is which.
Keita has further pointed out that this wiring issue with the grounding pins could indicate cathode and anode are swapped, which means that the diode will be forward biased, which is a much bigger issue.
Therefore, we're pausing on all BHSS work for now until we can figure out how to resolve these problems.
LLO has not checked their wiring, but Oli and I did note that they paid attention to the OMC labeling since they knew the cable lengths would be different.
When our OMCs were shipped to us, the ameristat wrapping had OMC A and OMC B labels, but once we took the wrapping off, there was no indication of A and B on the boxes.
Keita, Elenna, and I just went in and tested the direction the current is flowing for the DCPD cables (D2300118 and D2300119).
D2300118 (SN S2500546)
Current direction:
- Pin 2 -> 1
- Pin 5 -> 4
D2300119 (SN S2500548)
Current direction:
- Pin 6 -> 1
- Pin 9 -> 4
We verified that there was no current flow when probes were swapped