I asked EE to make/fix the whitening cables and/or install temporary new cables that are shorter than nominal, whichever is quicker. The shorter ones are to be replaced in the future.

Two cables were fixed, and the two new short ones were put in place. After this, I still saw that one of the two fixed cables (H1:ISC-Y-65, this is the first cable for WFSB) still had a short circuit for one pin. Since they didn't have enough short new ones, and since the broken bit was only for one of the whitening stages which I can leave off, I decided to keep the defective cable for now and live with it.

I also asked them to swap both of the whitening chassis, as the whitening gain was all over the place even though the BIO readback looked good, which didn't make sense, and we were getting suspicious about the whitening. The new ones were put in place.

I measured the dark noise, and both of WFSs had some problem.

For WFSA, one of the 8 channels (WFSA-Q4) would suddenly rail when the whitening gain is 24dB or larger. Up to 21dB it looks completely normal, DC output increases as I increase the gain, but when the gain reaches 24dB it suddenly jumps from a few hundred counts to 32k. Disconnected the analog, repeated it, the same result. Swapped the BIO cable, the same result. Since this seemed like a problem of the whitening chassis itself, I put one of the old whitening chassis (S1101600, which is one of the two units pulled out this morning) back and it behaved good. The problematic one is S1101636.

For WFSB, one of the channels (WFSB-I2) had much larger low frequency noise (f<1Hz) than everything else. You can kind of see that in the plot I posted yesterday, but today the noise looked larger. Disconnecting the demod didn't do anything as far as the low frequency noise is concerned, disconnecting the analog out DB9 on the whitening chassis didn't do anything, but when I went to the remote rack I immediately noiticed that the DB9 cable connector on the AA chassis was loose. I disconnected it and the noise was gone. I reseated everything, and things look good.

To summarize,

1. Whitening chain is in a workable state after fixing some nonsense problems.
2. Two short cables should be replaced, one bad cable (H1:LSC-Y-65) should be fixed/replaced, after this commissioning window.
3. Whitening chassis S1101636 seems to have a problem for Q4 channel (that's the last channel of 8-ch chassis).
4. It's not clear if S1101601 (which was pulled out this morning) has a problem or not, but we have some suspicion.
5. S1101600 for WFSA and S1101602 for WFSB are in use now.