I spent some time trying to debug our inability to get MICH onto REFL165Q while the arms are held off with ALS, to no real success.
I set up our usual repeatable situation of PRMI on 33 I&Q, arms held off with ALS. I figured that it may help to first sideband lock on REFL55, since 165 is looking for the f2 sidebands and maybe there is some odd offset between the locking points for f1 and f2 or other weirdness.
REFL 55 settings:
Demod angle 98->126 (was previously set for PRY locking)
PRCL = 0.5 * REFL55 I (UGF of ~200 Hz) (FM gain unchanged from REFL33 situation of -0.02)
MICH = 0.125 * REFL55 Q (UGF of ~60Hz) (same FM gain as 33)
Some REFL55 offset adjusting had to be done in order to not disturb the 33-initiated lock when handing off.
I also adjusted POP110 phase to zero the Q when locked, and switched the triggering over to 110I
The PRMI can acquire lock like this with arms held off with ALS, no problem.
Here, I tried to hop over to 165. PRCL was no problem, needing a +1 on 165I. However, I had no success in handing off MICH. I twiddled many knobs, but none that provably helped.
I saw indications that the sensing angle in 165 is small (~20deg), which is not consistent with current knowledge of the cavity lengths. We last interferometrically measured the PRC length by letting the PRMI swing and looking at sideband splitting in POP110. At LLO, they did a length measurement by looking at demod angle differences in PRMI carrier vs. sideband locking. (alog8562) This might be worth checking out...