2013-05-10 13:04:43 jaclyn.sanders@LIGO.ORG
    05/10/2013 - LHO - Modify (N.A.)
        05/10/2013 Jaclyn Sanders Modification Description
            Modifications as per E1200907. R271 to 0 ohms, R272 to NL.

2016-09-02 09:51:02 marc.pirello@LIGO.ORG
    09/02/2016 - LHO - Repair (LVEA ISC-R1 Rack)
        09/02/2016 Marc Pirello Modification Description
            D7, D8 (N4148W) were found to be blown and replaced.
            
            U28 (AD829) had differing voltages on the inputs, this was replaced and the voltage problem was verified to be solved.
            
            U5 (AD829) was had the same problem as U28, this op-amp was replaced and the problem was solved.
            
            U13A (AD829) was suspected to have an issue due to oscillation, this was replaced but the oscillation remains.  This is likely caused by bad biasing of the opamp when the gain is off.
            
            U59 (OP27) was suspected to be bad due to high noise and was replaced.  Changing it did not alleviate the noise issue.  This turned out to not be an issue, the MC chassis has more gain than the CM chassis we were comparing it to.
            
            A 200kHz low pass filter was added to the fast channel.
        09/02/2016 Marc Pirello Acceptance Test Description and Results
            All nodes of the signal path were analyzed with the SR785 set to noise measurement and every node was compared with the S1102622 chassis.  We noted no significant difference in signal path noise between the chassis. 
            
            Common Mode Servo Board Test Procedure was completed on August 31, 2016.  Some inconsistencies were found in testing but the unit performance was consistent with the previous test completed Sept 22, 2011 by R. Dodd.
            
            https://dcc.ligo.org/DocDB/0057/S1102626/001/S1102626-v1.pdf