Wire Wrapper needed for PDP-7

From: Tom Jennings <tomj_at_wps.com>
Date: Sun Feb 8 21:51:49 2004

I also agree it's a bad idea to strip. I meant to mention earlier, and
it's pointful here, is that a large part of the art of wirewrapping is
in the wrap schedule/wiring diagram. We used to spend WEEKS on that part
alone. There's a VAST amount of knowledge buried in there.

If you ahve wrap wiring schedule then maybe, but armed with just
schematics, it's a task likely to fail. There's actual subtlety in

>From experience:

*** Wirewrap is an unreliable technology. It relied on a mechanical
system to produce a gas-tight metal-to-metal seal, with dissimilar
metals, fraught with difficulty. If exposed to large tmperature swings,
especially over long periods of time, gas-tight is becomes not, and
resistance/impedance becomes erratic, and that matt of wire becomes a

Wirewraps killed my old Varian 622/I (18-bit) machine in the 80's.

Wirewrap is/was a prototype technology, applied to low-run production.
This stuff didn't have to live forever, and generally didn't.

*** BE WARNED that posts once-wire-wrapped, are not as reliable as new
ones! The rely on the sharp, square edge for that gas-tight connection.
Once wrapped, the edge is damaged. Used wirewrap posts are unreliable.

If there are no more than two levels used, you could solder each post,
but that woudl be unbelievably tedious and damage-prone. More than two,
and you probably couldn't get a soldering in there.

For bringing up the PDP-7, I'd concentrate on functional areas, if
possible. If you end up removing a wire or two I'd even go so far as
preserve paths and levels and wire guage.


On Sat, 2004-02-07 at 19:47, Ethan Dicks wrote:
> On Sat, Feb 07, 2004 at 04:58:03PM -0800, Al Kossow wrote:
> In response to:
> > Therefore, I need to take out all the modules, all the wires, and
> > start afresh
> >
> > This is a REALLY REALLY REALLY bad idea.
> >
> > It is hightly doubtful that someone completely rewired the backplane
> > of this system.
> >
> > If you start ripping out wires, there is 0% chance this system will
> > ever run again.
> I have to agree. I did this a long time ago to a damaged PDP-8/L (broken
> wires, broken enclosure, missing front-plex and broken front panel...)
> At the time, I had two and had _no_ prints. I still have the net-list I
> made from dismantling it (but it's of no value now that I have real PDP-8/L
> prints).
> I wish I hadn't done it now and I can only plead youth and ignorance (I was
> 16 when I got the pair of -8/Ls).
> The point of this is to say that completely stripping the backplane is
> probably a one-way activity. Documenting and removing the cards and
> cleaning the slots (with a sliver of manila folder soaked in isopropanol)
> on the other hand, is a good idea. That is entirely reversible.
> -ethan
Received on Sun Feb 08 2004 - 21:51:49 GMT

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