Well MC3 doesn't look healthy.

Above is my summary of Rahul's MC3 plots. P, R and V data is a pretty conclusive evidence that T3 actuation is 50% weaker than it should be. I'd like Fil to isolate the problem to DAC side or the driver side by following https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=57151, and if the problem is in the driver then swap the driver right away.

(Not sure how to make sense out of LF and RT coils, L TF is on top of the reference seems to mean that they're fine, but Y trace is about 2 dB lower than the reference. But LF and RT are on the same driver chassis as T3 coil. We'll revisit all coils on this chassis after we swap the driver IF we swap it.)

If it's on the DAC side we need to talk again.

MC1, PRM and PR3 look OK to me, all traces are within 1dB of the references.

But anyway, to REALLY make sure that all of these are working fine, probably it makes sense to measure M1 COUIOUTF_IN2 to FASTIMON transfer function for all of these suspensions including MC3 again after we fix MC3 T3 problem.

Corresponding FRS ticket 16116 for "MC3 top T3 coil output is about 6dB weaker than others".

Finally exporting and processing this data for H1 SUS MC1, and along the way improving the templates, as I continuing the campaign to keep up librarianship with the history of all SUS (and today motivated by understanding the diversity in pitch mode frequencies among the builds).

See attached first .pdf for "individual" comparison against the model, which includes cross-coupling and OSEM basis response.
The second two attached .pdfs show comparison against all the recent history of this SUS, and a few other examples of the same type.

I agree with the assessment that the SUS looked healthy at this time.

J. Kissel 
This is a repeat of the information in LHO aLOG 60763 excepted for the "individually" processed set of TFs in the first attachment. These show the cross coupling and OSEM basis transfer functions which could be helpful in diagnosing problems like this in the future 

Finally exporting and processing this data for H1 SUS MC3, and along the way improving the templates, as I continuing the campaign to keep up librarianship with the history of all SUS (and today motivated by understanding the diversity in pitch mode frequencies among the builds).

See attached first .pdf for "individual" comparison against the model, which includes cross-coupling and OSEM basis response.
The second two attached .pdfs show comparison against all the recent history of this SUS, and a few other examples of the same type.

The comparison between the 2018-01-03_2135 data (cyan), this 2020-04-15 data (green), and the much later and latest 2020-10-29_1530 (red) show that MC3 was *not* healthy during this time.
Later investigations revealed that one leg of the differential analog output for the corresponding AI chassis that drove MC3's T3 coil had somehow gone bad between the O2 to O3 2018 and 2020 upgrades -- see documentation of the problem only after the 2020-10-29 data set in FRS Ticket 16116, and the most helpful / descriptive aLOG about it, LHO aLOG 57172.

The last comment in the FRS Ticket and that LHO aLOG 57172 suggests that the problem was fixed. However, we did not take a confirmation set of transfer functions after the fix.

We should get a new set of TFs at our earliest convenience.

This failure mode will be a nice one for the https://awiki.ligo-wa.caltech.edu/wiki/TransferFunctionColoringBook.