Excellent advice...
Lyle
On Sunday 08 February 2004 05:01, William Maddox wrote:
> Tore,
>
> If I understand you correctly, you are saying that major subsystems were
> added to the CPU and wired into the backplane by a former user, who removed
> these components without regard to its effect on the operability of the
> machine before you came into possession of it. That wouldn't surprise me
> at all. Many academic and lab shops did extensive custom modifications,
> like the famous BBN paging box on the Tenex KA-10s.
>
> If this is the case, then clearly you've got your work cut out for you. I
> would caution you against assuming that the maintenance manual is complete
> and accurate for your machine. These machines went through multiple
> revisions and field ECOs during their lifetime. There was a set of field
> maintenance prints issued for the specific revision that a customer had,
> which was then kept up to date with the machine. (At least this is true of
> the Straight-8 of similar vintage.) It is even possible that you will not
> have exactly the same cards as documented in the manual, so certainly check
> this before pulling any wires loose! Consider an ECO that requires an
> extra gate or two, for example.
>
> I think the most prudent course of action would be to leave the existing
> wiring in place for now, but to carefully trace out what modifications
> were made and note what wiring has been added and removed. The pictures of
> the machine show some wiring of a different color -- frequently new wire
> added during customer modifications or ECOs would be a different color
> precisely to make it easier to identify, so you might want to see if that
> theory checks out for your machine. Once you understand the nature of the
> modifications in detail, then you can undo them. Wire-wrapping is tedious,
> so you might as well avoid as much of it as you can. A young guy like you
> might be able to trace out the wiring by eye, with a little help from a
> continuity tester (cards out for this unless you have a "zero current"
> tester) and a probe to displace wiring that is obscuring your view. A
> better bet might be a "fox and hound" type device such as described on
> Aaron Nabil's "Tools and Tips" page: http://pdp-8.org/tools.html If you
> have any contact with the original owner, it would definitely be worth
> tracking down any information that you can dig up on the nature of the
> modifications, even if the detailed wiring changes are not documented, just
> to help you make sense of them and sort out what were customer changes and
> what might simply have been manufacturing differences and ECOs relative to
> the maintenance manual that you have.
>
> As mentioned by others, it would indeed be a good idea to pull all of the
> cards and clean the connectors. I would recommend labelling all of the
> cards first with their locations, and not assuming that cards of the same
> type are interchangeable. Some of the flip-chip cards may have trimpots or
> jumpers that are adjusted for their particular role.
>
> Good luck!
>
> --Bill
--
Lyle Bickley
Bickley Consulting West Inc.
http://bickleywest.com
"Black holes are where God is dividing by zero"
Received on Sun Feb 08 2004 - 08:58:46 GMT