(Corey, Gerardo, Patrick)
Two days ago (about 4am Thurs morning) the ISS diffracted power started to drift down from about 6.7% down to 2.0%. Once at 2%, it started to go into oscillations (roughly around 3am this morning); see attached 2-day trend.
Without instructions on how to address this (and no recent alogs noting this behavior), we scratched our heads a bit, moved some gains and hit buttons to no effect. We returned back to the original state. Then Patrick suggested we try switching from PD A to PD B, and this appeared to stop the oscillations. It took us to a value of about 5%. Unfortunately, it looks like the power is still sloping down however. (Curious to see if the ISS goes back into oscillations at 9pm tonight).
Actually switching PDs was not the way to go here; we generally want to stay with PD-A.
So here, you want to adjust the REFSIGNAL (H1:PSL-ISS_REFSIGNAL) channel in 0.01 amounts. With Rick on the phone, I went from -1.63 to -1.55. This stablized the Diffracted Power and took it from ~2% up to ~10%.