MichaelR, RickS, VolkerQ
After realigning the auxiliary beam hitting IO_AB_PD1 on the PSL table we found that there was a strong 800 kHz amplitude modulation on the light transmitted through the PMC. It was a strong modulation with about 20% of the total power oscillating with a nice ~800kHz sinewave. The ISS was not happy and would not stay locked.
Fix: Switch noise-eater off and on. This resolved the AM issue.
But even after that the ISS would not engage. The voltage on ISS PD A and PD B was ~ 6V and we increased it to 10V. This made the autolock
work again, but IO_AB_PD1 again showed a strong AM modulation. This time at ~80 kHz. We reduced the gain of the ISS from 9.2dB to 8dB and now the ISS appears to be happy again. No obvious oscillations on IO_AB_PD1 are observable.