Yuhang, Eleonora

During the "ADC trouble" we found out that PR oplev PSD was not working fine: 

- SUM channel was giving a negative output

- Y channel doesn't respond to vertical movement of the beam position on the sensor

We replaced the PSD with a spare one.

[Note that this spare was previously used for BS oplev (see elog #1947) and we changed it as we suspestected it was noisy but after the replacement we kept oberving occasional noise floor excess in BS so we confirmed that it was not PSD fault.]

After the replacement I mesaured the TF of PR (pic1) and found that it perfeclty overlaps to the previouse one, so I didn't need to modify the gain of the damping loops.

We suspect that PSD falilure can be connected to the AA burnt card. Investingations are on-going.