= Fix of MC servo board circuit =
[Awai, Nagano, Enomoto]

We fixed the problem on the common mode servo circuit.
Summay:
We replaced op-amps named U3 and U5 (see D1503567 and S1503859) with new ones, and the circuit worked properly.

What we did:
Since we knew input amplifiers were suspectable, we checked op-amps around there. Then we found that U3 and U5, which are the first op-amps the signal goes through, were broken; the output of these op-amps were -15 V and two inputs were not virtual short. Other op-amps seemed to work properly.
Then we replaced these op-amps with new ones.

Thank you very much, Awai-san, Kamiizumi-san and everybody concerned!!
 

= Fix of IMC model=
[Miyakawa, Kokeyama, Nakano] (Sorry but I don't know exactly who worked on this issue.)

Since yesterday the channel names of IMC model had gone crazy.
By correcting the filter names in the model, they got the channel names back to the former and correct ones.
Additionally, they needed to restore filter banks. They restored the filters from backup files and did "minor" changes on the foton file "IMC.txt".

Now the digital control on IMC works as before.
 

= IMC lock restored =
[Nakano, Nagano, Enomoto]

We re-installed MC servo in IOO rack and tuned the common gain of the IMC length control loop. IMC lock is restored.
Summary of parameters and UGF:
-- amplitude of RF voltage source   -20dBm
-- IMC trans   ~ 0.455
-- common gain (K1:IMC-REFL_SERVO_IN1GAIN)   -7 dB
-- UGF (measured)   32 kHz,    phase margin   58 degrees

Note:
-- We paid attention to voltage supplying; we first turned off the voltage supplies (17 V and 24 V), connected the power supply cables, and then turned on the voltage supplies simultaneously.
-- IMC REFL beam was centered on the RFPD.
-- Currently INPUT1 is used instead of INPUT2, which has been used, because now the strange behavior of INPUT1 has also been solved.
--100 kHz LPF is implemented on the generic filter stage (see klog 1350), and it seems to work properly.
-- We tried to increase LO level, but gave up doing it today, because the IMC lock looked unstable. We then restored the previous settings (-20 dBm).