Tough to Diagnose issue with PDP 11/40 CPU

william degnan billdegnan at
Thu Jun 30 09:58:50 CDT 2016

On Thu, Jun 30, 2016 at 10:21 AM, Noel Chiappa <jnc at>

>     > From: William Degnan
>     > The problem was a missing KJ11
> Ah. Well, if you want to add one (I assume you've just re-jumpered the
> machine for the moment), I do have one we can copy (for the PC etch) - I'm
> assuming here that originals are now unobtainium.
> Also, if you have the KE11-E, but not the KE11-F (the former is a prereq
> for
> the latter), and would like one, I have one I have no use for (Unix doesn't
> use that version of the PDP-11 floating point), and would be willing to
> trade
> it for something I do have a use for.
>     > My error. Lesson: Always check everything.
> Yes, always a good rule when dealing with recovered machines. I always take
> them apart and go through them completely, verifying all cables, etc from
> the
> original documentation.
>         Noel

Actually I had one, put it in, fixed problem. i.e. I kept the jumpers
as-is, added the KJ11, system now works better in that I can load BASIC,
diagnostics, etc.  Does not mean the system is perfect though, but I have
been able to move to the next point in the troubleshooting process - Goal
to boot RT-11 from an RL02.
@ BillDeg:
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