Following on after-HAM3-closeout tfs results of lowest stages of PR2 -which were showing high q resonant pole at 45 Hz in the M3 L-LR transfer function-, and in order to determine if the problem is in chamber or in the electronics chain, I swapped middle stage and bottom stage cables at the in-air vacuum flange of HAM3 (respectively H1:SUS_HAM3-25 and H1:SUS_HAM3-26), and took those measurements again.
As showed on the attached screenshot, the pole moves to the M2 LR-LR tf after swapping the cables, and disappear on the M3 LR-LR tf, which eliminates issues in the electronic chains, and indicates that the problem is in-chamber.
Obviously, the cables were swapped back to their nominal position
In order to find where the cable at the vacuum feedthrough is, I used the wiring diagram D1000599 indicating Middle and Bottom stage of PR2 are plugged to feedthrough D6. The flange layout D1002874 indicates D6 is on the South-West side of HAM3 but the cables were found to be plugged in the North-East side of HAM3.
It should be noted that the 45.3 Hz feature is also clearly visible in the power spectra for the M3 LR channel (see attached), which may also help with quick diagnostics/debugging in future.
