[Kawamura, Aso, Kokeyama]

This morning IMC suddenly stopped working (around 9.30 AM). Looking at digital monitors (I use /users/dc/IMC-COMM-MOD-SERVO-MON.xml), all the monitoring signals for error and control signals were zero, as if analog error signal was lost.

So we entered the mine and found that analog error signals were not coming out from the PD. Power from Dsub cable seemed fine, and test input-out put worked fine, though. Only the error output was broken, it seemed. We swapped MC REFL RF PD to a spare one and IMC is back working OK. We do not know what part in the RF PD circuit broke.

With the new PD, fine gain adjustment was not done yet. We increased the fast path gain from -3dB to 0dB (K1:IMC-REFL_SERVO_IN2GAIN).