New find - OSI Challenger 4P

Wheeee! I got an OSI Challenger 4P today (does this complete my collection of early micros with walnut sides? I now have my Sol and NorthStar Horizon and Challenger.) Of course it would be even better if it worked or at least I had some documentation. A shielded cable terminating in an RCA phono plug exits the cabinet. The fan turns and apparently something is being output. I tried a mono composite monitor with no luck, but channel 11 (?) seems to give what could be a screen image with several inverse video blocks scattered down the left side (we have a STRONG channel 3 here, and 4 is garbage). Pressing "return" shows no change in the screen, nor does pressing a momentary-contact switch (home-brewed?) above the keyboard labeled "Break Enable." Since I never even saw one of these in the 70's, I could use some help. Does anyone have docs they would be willing to copy for a reasonable fee? Any other advice cheerfully accepted. Bob Stek Saver of Lost Sols