Difficult to see but it is making markers on the horizontal sweep without the RF input!
The bad news is there was a hardware issue with the 8600. To be honest, after cleaning, switching, spraying etc I did a Shango and picked the front of the instrument up about an inch from the bench and let it bang on the base and viola! The markers appeared. It must be a bad solder joint on one of the boards or a board plug-in not making good contact. Not going to touch it until I get the alignment work setup and then I'll carefully reposition it where it's gonna live. Eventually I'll need to run the issue down.