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From: binder@dosadi.DEC (Wherever you go, there you are.)
Newsgroups: net.micro
Subject: Re: How to fab One-Of-A-Kind systems?
Message-ID: <2087@decwrl.UUCP>
Date: Thu, 9-May-85 09:50:51 EDT
Article-I.D.: decwrl.2087
Posted: Thu May  9 09:50:51 1985
Date-Received: Sat, 11-May-85 09:12:13 EDT
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
Lines: 32

I second the motion for wire wrap, very loudly, with one caveat:  if your
hardware will include any extremely sensitive analogue stuff, eg the National
Semi DP8460 disk data separator, then you have to PC that area - Radio Shack
PC kits work fine, if you're careful.

I used to work for ModComp, and until 1978 virtually all ModComp hardware was
wire-wrapped.  Done properly, wrap is as reliable as any other technology, and
it is, as was pointed out, a lot easier to fix.  If you're serious about being
able to fix things, don't use a slit-n-wrap gun or any other tool that wraps a
continuous string.  Instead, lay out your strings so that the second, fourth,
etc. wires in a string are wrapped at first level, next to the board, on both
ends, and the first, third, etc. wires are wrapped at second level.  That way
you never have to remove more than three wires to add or remove any single
node in a string.  During debug, you can connect new pins to an end of the
string, or you can cheat and go first-to-second in the middle of the string.

A comment on socket reliability is that sockets are also as reliable as might
be desired.  BUT, and it's a big but, there are two kinds of sockets.  One is
called a face-grip socket; it grips chip pins on the inside and outside faces,
which are wider, thus providing (it is claimed) more area of contact.  The
other kind is called an edge-grip socket; it grips the pins on the edges
between pins.  Face-grip sockets grip with less contact pressure, and the
advantage of the greater area is lost.  Edge-grip sockets have a MUCH higher
clamping pressure, and they provide a good gas-tight seal between the socket
and the pin.  FACE-GRIP SOCKETS ARE UNRELIABLE!!!  EDGE-GRIP SOCKETS ARE VERY
RELIABLE!!!

Cheers,
Dick Binder   (The Stainless Steel Rat)

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