VT101 8085 CPU Fault

The terminal controller board on my VT101 is not working, if it displays anything it is random characters. I have used my scope to check the 8085 CPU. It has power, it is outputting a valid clock, but there is no activity on the RD,WR and ALE pins. I am guessing the 8085 is bad, but before I go replacing it I wanted to check if anyone knew of anything else that might cause the 8085 to misbehave (ie am I seeing symptoms or a cause?). It looks to be easy to get 8085s, if I replace it I will socket it at the same time, but would rather avoid having to desolder it if the problem is elsewhere. Any advice gratefully received. Thanks Rob PS Just to check that the rest of the terminal works, I substituted the terminal controller board with one from a VT102 and it worked perfectly. So the problem is definitely on the terminal controller board.