We have been reporting in various alogs about locklosses where the yaw ASC signals have a large motion right before lockloss (85935, 85841, 85948). I have narrowed it down to the TMSX suspension moving largely in yaw. TMSX yaw moves first, and the ASC signals follow. The TMS servo, which adjusts the TMSX TEST offsets to center the beam on the TMS QPDs follows the TMSX yaw motion. We can see that the F2, F3 and F1 oseminf outputs move by about a half a micron just before these locklosses. However, the MASTER OUTs don't see a large drive, so this is something that the sensor is seeing.

There is also no movement in the HEPI IPS, ISI GS13 or ISI CPSs, which leads us to believe this is due to something at the suspension level.