Well, I feel somewhat stupid, but the problem with the hung bus is solved.
The cause of it? no jumpers on the backplane to bypass the battery backup.
The machine had a BBU regulator, but it was removed as I don't have the
battery pack. So, after adding the 3 jumpers the NPG signal was cleared
after a cntrl+halt and characters could be printed when deposited at
address 777566 (with memory in the backplane).
So, next step is to add a RL11 controller and see if it will boot RT-11.
But that is for the weekend....
Ed
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