vintage computers in active use
elson at pico-systems.com
Fri May 27 11:35:33 CDT 2016
On 05/27/2016 01:30 AM, Eric Smith wrote:
> I wrote:
>> Another CHM volunteer (from the PDP-1 Restoration Project) and I
>> pushed for an IBM 360/30 Restoration Project, and the ability to build
>> replacements for failed SLT modules was part of our plan.
> On Thu, May 26, 2016 at 9:40 PM, William Donzelli <wdonzelli at gmail.com> wrote:
>> I am still trying to figure in which universe are SLT modules so rare
>> that one needs to fabricate replacements.
> As far as I can tell, if I suddenly need a specific SLT module, the
> odds of finding that specific module at any given time on eBay is
> essentially zero.
> Obviously if we could find an authentic replacement, we'd prefer that.
> We didn't want the entire restoration to be dependent on having to
> find authentic replacements.
> Some SLT modules are far more common than others. I don't know how
> many different SLT modules are used in the 360/30, nor what percentage
> of the SLT modules in that machine are common ones. When we restored
> the DEC PDP-1, it contained quite a few DEC System Modules from DEC's
> standard catalog and that we had spares of, but it also contained a
> non-trivial number of specialized modules that are much harder to
> find, if not impossible. I'm guessing that IBM machines were probably
OK, there are hundreds of different SLT "cards", ie. the PC
boards. But, reading some FE docs on bitsavers, it seems
that all SLT 360's were built with 95+ % of the SLT
"modules" consisting of only 6 types. (I've never
understood why the SLT modules had to have 8-digit or
something part numbers if there were only 6 types.)
So, when I was talking about making replacement SLT MODULES,
I meant to fabricate tiny 1/2" x 1/2" PC boards with 12
leads, that could be mounted where the failed small SLT
module had been.
In IBM terminology, they have SLT modules, which are 1/2"
square ceramic substrates with thin-film resistors fired
onto the ceramic, then silver-bearing conductors are printed
on and fired, and finally bump-bonded transistors and diodes
are soldered onto the conductors. A drawn aluminum cover is
epoxied to the ceramic.
Then, these modules are installed on boards, which can be
single-side or double wide. They have connectors on one
edge, which plugs into a "BOARD".
The boards were roughly 9 x 12", I think, and had rows of
pins on both sides. The SLT cards plugged into one side of
the board. The boards were multilayer, and the inner layers
distributed power and ground. Surface layers had
application-specific wiring. Then, more wiring was added to
the back side with wire-wrap wire. Also, around the edges
of the board, there were places where 18-signal transmission
line cables could be plugged.
These had the same layout as the SLT card connectors, 24
contacts on .125" spacing.
The transmission line cables were clear flat ribbons with 3
wires per signal. So, they went
ground-signal-ground-ground-signal-ground, etc. The
neighboring ground wires were much closer together than the
ground-signal spacing. These had a characteristic impedance
of 93 Ohms, I think.
On IBM 370's they split up these cables into individual
signals to reduce crosstalk. They retained the
3-wire/signal scheme, and called them tri-lead.
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