USR quad modems... (ontopic - really!)

Don THX1138 at dakotacom.net
Fri Aug 18 11:09:15 CDT 2006


Dave McGuire wrote:
>> <grin>  I worked on a "600 pin tester" (i.e. be able to
>> stimulate and monitor the states of 600 different signals
>> on the unit-under-test) in the late 70's.  The "stimulus
>> memory" was two "doors" (large -- ~18" x ~60" -- wirewrapped
>> panels on hinges fed with *thick* copper bars for power
>> distribution) full of bipolar & ECL memory devices.
>> I.e. *hundreds* of amperes.
> 
>   Holy cow!!

Yeah.  Before starting work each day, you would remove
your wristwatch, wedding ring, belt buckle, etc.  Sure,
everything was "low voltage" (I think the pin drivers
max'ed out at 64V -- or maybe 32?  The power supplies
were digitally programmable so it was some nice binary
number...).  So, you weren't worried about getting
electrocuted but, rather, *cooked*!

One of my buddy's could never get his wedding band off
so he would have to wrap it in a bandaid.  Of course,
bandaids are (back then) pseudo-flesh-colored so the
standing joke was that he was having an affair and
needed to keep his wedding band/marital status out
of view!  ;-)

>> When the boards came in from the wirewrap house, there was a
>> short between two of the supplies (or, perhaps, a supply
>> and ground).  Trying to figure out *where* the short could be
>> in a panel of that size COVERED with teflon wires was HUGELY
>> intimidating!
> 
>   This I can also imagine!  I remember how much trouble it was to find 
> wiring errors in Unibus-sized boards.  If I recall correctly we had an 
> average of 350 chips per board, and tens of thousands of wires.

And it's all (deliberately) point to point so it's truly
tangled.

I still am unconvinced that the beast could actually *work*
given that *apparently* random fabrication technique (the array
was clocked at 100MHz -- no, it must have been 125MHz because
the cycle time was 8ns).  Perhaps the designers had carefully
considered *placement* of the components and thus indirectly
influenced signal lengths, etc.   <shrug>

TIP:  An embroidery hook works wonders for fishing wirewrap wires
out of a nest without too much damage!  ;-)  (but you have to
find the right size hook to ensure a "good grab" on the wire)



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