Problem(s) Encountered:

Around 10p.m. I couldn''t see any star on the frames made by CCD camera. I thought it was because the weather, but the weather was fine. It looked like a shutter closed. I reset both cameras, it didn''t solve the problem. I decided to close the telescope. During this procedure, I saw communicate ''mirror both open and closed'', I checked that visualy, but mirror was closed. I put telescope to home position. I reset all computers. Then, I turned on computers and cameras again.  Still, the exposures made by CCD camera looked like with the closed shutter. It was midnight, so I decided to stop observing.

Solutions:

It appears that one of the preamps (the one associated with 4x gain) has failed.  Camera has been sent to the vendor for repair.