J. Kissel, S. Dwyer, E. Capote

We recently re-discovered that H1SUSPRM M3 DRIVEALIGN matrix has an L2P filter ON with gain of -1.36 that was designed in 2014 (see LHO:9589). Unsure of its function/performance with the modern IFO, we wanted to test turning it OFF. We turned it OFF (by ramping the gain in that bank to 0.0 with a 10 sec ramp time) at the end of the most recent lock stretch, with the IFO in nominal low noise (just after Elenna's calibration push; LHO:87520). Namely the IFO was suffering from a failed H1 SUS ITMY PUM sat amp, and we knew we needed to replace it, so we were looking for "useful" ways to break the lock.

Turning off the H1 SUS PRM M3 DRIVEALIGN L2P filter, at first superficial glance, has no impact on the IFO excpet for reducing the M3 pitch drive from +/- 300 to +/- 2 (Euler Basis) DAC Counts.

For more in-depth analysis, 
    - 2025-10-16 18:45 UTC the problems with the ITMY satamp started
    - 2025-10-16 19:54 UTC we turned off the PRM M3 L2P filter, and
    - 2025-10-16 20:02 UTC I caused the IFO lock loss by inverting the polarity on IN2 of the IMC common mode board.

So, we should have a good 5 minutes of time right before vs. right after to compare ISC ASDs.

We also tried this next lock acquisition with the filter OFF, to see if it's still needed for lock acquisition.
PRMI isn't locking after 10 minutes of trying (*after* going through MICH fringes), though we did NOT run an initial alignment prior to this lock attempt and the AS port does look a little splotchy.
Turned it back on 2025-10-16 20:39:44 UTC, but pretty quickly decided to run initial alignment instead (by 2025-10-16 20:42:57 UTC).
We'll leave it ON and test more / again some other day; we'd rather get back to observing.