This morning we had a hard time relocking FSS.

I bypassed auto-locker's  gain ramping (auto-locker automatically ramps the input to H1:PSL-FSS_COMMON_GAIN_CALI filter from zero to H1:PSL-FSS_COMMON_GAIN after it thinks that the FSS is locked to the right mode for more than H1:PSL-FSS_AUTOLOCK_DELAY1) by disabling the input to H1:PSL-FSS_COMMON_GAIN_CALI, set the resonant threshold low so that the auto locker wouldn't restart scanning, and observed what's going on.

It seems like there was some oscillation going on, shown in green and blue in the attached left (these are the IOP channel for FSS_MIXER_IN1). I cannot tell if this was really as low as 3kHz or if this was just aliasing.

Oscillation didn't change much as I changed various things e.g. re-enabling the gain ramping with smaller common gain, larger and smaller fast gain and  different PMC locking gain.

After 10 minutes or so while left in oscillation while I was trying things, the error signal started decreasing, the peak went higher in frequency (blue trace in DTT is 2 minutes younger than gree), and after 19 minutes suddenly the oscillation is gone (red trace in dtt).

It's locked now, but it's probably worth going to the PSL room and see signals on the oscilloscope as well as the network analyzer when this is going on.