We found that the reference cavity had lost lock.

I relocked it by disconnecting the fast and slow inputs, tweaking a bit the temperature knob and re-connecting the input cables.

The cavity is now likely locked to a different FSR from before. This means that the beat note at the end station might now be falling out of the PD bandwidth.

We have to go to end Y and adjust the ALS laser temperature to get the beat note in the PD range again.