As we had the recurrent problem of the intermittent failure of one of the CCDs again at the start of the semester, we got replacements for the internal dewar wires to the CCD which we thought caused the problems. After that it was not possible to reproduce the fault, the detector bias-level returned to its commissioning state and a successful two week run followed.
During a run in June the problem of an intermittent failure of CCD11 returned. From test in the clean-room it was found that there is a problem with the video channel used by CCD11. Each video board has two analogue channels and for all the four CCDs only one channel on each video board is used. Swapping the damaged video board with another that does not use the broken channel, signal was seen from all four devices and things seem to work properly. However, some unexplained features are see in the form of high and low columns in the CCDs which need to be tested. It should also be noted that all tests have been done at room temperature. Furthermore, this faulty video channel can not explain the apparent ``gravity'' related properties of the fault at the telescope. Further tests are planned, including `cold' test on and off the telescope.
Thomas Augusteijn 2010-02-09