There were no faults causing more than 2 hours downtime during period 38, but there was one problem that caused small amounts of down time on various occasions. This same problem continued in to the current semester causing some more down time bringing the total down time caused by that fault to be over 2 hours so I will discuss it here.
On several occasions the filter wheel of the guide camera became misaligned vignetting part of the field of view causing problems with the detection and centering of the guide star. Both mechanical and electronic problems were suspected, but more detailed investigations did not show any specific problem. Some changes were made in the way the filter wheel was operated which at first worked very well. In the end things deteriorated quickly at which time it became apparent that a problem in the controller of the filter wheel caused it to work intermittently. Replacing the controller solved the problem.
Thomas Augusteijn 2009-05-14