[Kiwamu with a help from Christina@AEI remotely]

 Today I made some efforts to bring the ISS back on by following an instruction by Christina and made it sort of running --- the loop can be closed by the autolocker but the diffraction power seems bit too high and also the gain seems too low. Certainly the ISS needs further investigations.

• Reference signal
  • Initially I tried to set it to be 1/5 of the DC signal of PDA which was 8.5 V.
  • -1.7 V at the reference signal didn't work -- it unlocked the ISS loop because of a too big signal at OSCILLATION_MON_LP.
  • I empirically ended up with a reference of -1.62 V which seems giving us a stable lock.
  • However this gave me a big diffracted power of about 16 % and I guess this needs to be about 10 % according to the strip chart in the ISS medm screen.
• GAIN
  • Initially this was set at 7 dB.
  • I increased the gain by 6 dB but it seems that a higher gain induces an unknown oscillation at about 100 kHz. This was clearly visible at the outer loop PD output in an oscilloscope.
  • Toggling the noise eater didn't change the situation.
  • So the gain was set back to 7 dB.