Plot shows OSEM IN goes to zero, pitch goes to zero, but the COILOUT drive and voltmon remain essentially unchanged from before and after the event at 11:15UTC.
I cannot change OSEM values with alignment slider or by removing all drive from the coils.
Plot 2 shows all of the IMs and MC1 and MC3.
IM4 Trans oscillates after the event, then is quiet.
I have already mentioned the possibility of a broken wire, to explain this event.
Cheryl's last sentence is pretty scary, so I would like to emphasize that this is not a suspension wire breakage event.
Note that IM4_Trans, other than a quick glitch, remains totally constant in spot position before and after this "event". The IM2 glitch happens at the left side of these plots (IM2 readbacks are the top left plots in Cheryl's attachment 2). The IMC does not lose lock until much later, and we see the IM4 Trans pitch and yaw in the bottom corner of Cheryl's attachment 2 is nice and happy until the IMC loses lock.
Work is still in progress to diagnose exactly what happened, but I suspect that somehow the OSEM readback channels went dead, which (since we use them for local damping) caused a transient signal to go to the coils, which caused a brief alignment glitch. Now the damping is obviously bad since we don't have valid signal going in, but the overall alignment of the optic seems not to have moved.
So before we vent I went and looked at the signal chain. I replaced the Sat Amp S1100173with a new one S110091. This has signals returning to the system. Normal may be up to someone else.
Opened and Closed FRS Ticket 6098.
IM2 is damped and realigned to restore pointing on IM4 Trans.
Change in satelite box means the IM2 pointing was not restored with the old OSEM values.
I realigned IM2 to restore the IM4 Trans values, which puts the IM2 OSEM pitch and yaw readings at p = +611, and y = -195 (old values p = 603, y = -204).
IM4 Trans values were p = -0.525, y = 0.095, now restored (IM1, IM3, and IM4 were restored earlier today).