VT101 8085 CPU Fault

Robert Jarratt robert.jarratt at ntlworld.com
Sun Jan 18 12:55:29 CST 2015

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


Any advice gratefully received.






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.

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