IBM 5100 Serial Number Project (and a question or two)

I just received a 5110 (BASIC-only, no tape drive) with serial number 30163. I've got a couple of quick questions for the experts. First off, I think I may be getting an error on startup. When I power the system up, the display shows AACCEEGG on the top line. After five seconds, AACCEEGGJJLLNN RRSS44 is displayed on the top two lines. One second later, AACCEEGGJJLLNN RRSS11 is displayed on the top two lines. After three seconds, the top two lines are erased and LLAA00 _ _ (two flashing underscores) EEDD is displayed on the last three lines of the display. Actually, when the display switch is set to "64", the above strings appear on both the left side and center of the screen. Is this some sort of error display? Does anyone have any sort of error summary for the 5110? The "Process Check" light remains dark. Hitting the keys produces no result. Second question: what's the BNC connector on the back of the system for? I read somewhere that the 5110 and 5120 had composite video output, but I'm not sure. -- Tony