
Inside the Apollo Guidance Computer's Core Memory - NelsonMinar
http://www.righto.com/2019/01/inside-apollo-guidance-computers-core.html
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zaarn
If you look at the youtube channel "CuriousMarc" (just search for it, they
have multiple restoration videos), you can look at this project in video, the
latest video shows their attempt at finding the module's problem via XRay at
the end, the other videos detail earlier parts of the operation, including
booting up the AGC with original code fed from a ducttape-design
FPGA/microcontroller. It's a very interesting video series to follow.

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DennisP
My dad spent his career as a customer service engineer for IBM. When I was
about seven years old, back in the '70s, he took me to work at one of his
accounts, the Washington Post. He showed me their room full of mainframe, and
opened up a cabinet of core memory, thousands of wires and tiny donuts. Now
and then, when I use a thumb drive with hundreds of billions of stored bits, I
think of the day when I could see every individual bit in a box almost as big
as I was.

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userbinator
_We attempted to find the location of the broken wire with X-rays, but couldn
't spot the break. Time-domain reflectometry suggests the break is
inconveniently located in the middle of the core planes. We are currently
investigating options to deal with this._

Depending on what it was potted with, dissolving the potting to repair it
might be feasible. Many others have done this with (admittedly less rare and
fragile) not-easily-replaceable electronics before, but it's a difficult and
time-consuming process. The 38AWG wire is ~0.1mm so the traditional "pick out
bits of potting" method is unlikely to keep the wire intact --- something more
like dissolving and gently washing away the compound would be preferable.

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kens
We figured that if the break was near the outside of the module, we might be
able to dissolve the potting around the break. But unpotting the entire module
to search for the break has way too big a chance of breaking more wires or
causing more damage.

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workmandan
Great write-up. If you haven't seen it yet I'd highly recommend watching the
entire YouTube series (part 6 is linked at the end). Some fantastic
engineering!

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setquk
Fantastic article. I wish I was born a lot earlier so I could work with these
discrete and semi-integrated devices. they looked so much more fun than modern
electronics which is just "bus the ICs together".

