MDM Trouble Report for 2007 Apr 23 Telescope: 2.4m Observer(s): Sharma & Statler (Ohio Univ) Instrument: 8k CCD Camera Problem(s) Encountered: We had numerous problems with CCD controller communications, mostly connected with board 2. In our attempts to recover, we went through the process of powering off the slave and master power supplies, detaching detcom, hitting the resets on the back of 'vesuvius', powering up master and slave, and restarting detcom at least 10 times. Problems began when we slewed the telescope east for evening twilight flats. A garbage from board 2 error appeared while we were slewing, following which we were unable to take exposures or to turn the slave high voltage on or off. It took 3 or 4 attempts to get the instrument back up. It then performed adequately through several hours of observing, until 1:15 AM, when we again slewed to a couple hours east of the meridian to pick up a new object. We didn't get an error message during the slew but exposures started failing right away. We tried the recovery procedure several times with no success. To test whether the problem was associated with the angle of the telescope, we brought the telescope back to near the meridian. The recovery procedure then succeeded, but then the problem recurred when we tried to slew back to our target. During our subsequent repeated recovery attempts the situation degraded to the point where slave communication was totally lost (no green light on the back of vesuvius). Eventually we decided to slew partway back to about HA = -1hr; at this position we were able to recover function of the instrument. We then shut off tracking and waited about 25 minutes for our target to catch up with the telescope. After this we were again able to observe normally for the rest of the evening, although we were paranoid and stayed on a single target and avoided slewing for morning twilight flats. We also noticed a very odd thing about bias values: in any sequence of consecutive bias frames, the mean counts alternate, high-low-high-low-etc. (The sequence is acquired using the DETCOM commands: etype b; go n [with n>1].) The high-low variation is several tens of counts, i.e. many times the standard deviation, even accounting for the (now much reduced) grounding pattern noise. What's more, the high and low values show a monotonic increase or decrease within a sequence, both going in the same direction. This is true on all chips. The overall bias levels are not stable over the night, either. But this last part may have something to do with our powering on and off the controller due to the problems mentioned above. ------------------------------ Submitted on 2007 Apr 24 [5:54:09]