In preparation for disconnecting cables in HAM1, I turned off the following DC interface chassis:
LSC RF PD DC interface chassis in ISC R4 (REFL-A, POP-A among others), LSC RF PD DC interface chassis in ISC R1 (REFL-B among others), and ASC WFS DC interface chassis in ISC R4 (REFL_A, REFL_B among others).
Daniel will perform TDR to measure RF in-vac cable length from outside.
Turning off the DC interface for LSC REFL_B somehow interfere with FSS locking. Turns out that the DC interface provides power (and maybe fast readback of the DC output) of FSS RFPD.
Since the point of powering down was to safely disconnect the DC in-vac cable from LSC REFL_B, and since the cable was safely disconnected, I restored the power and the FSS relocked right away.