Apollo Guidance Computer Part 18: Module B11 rescue, Apollo 13 style

After having repaired two diode faults in our potted current switch module B11, we discovered a third fault. This time it's a short, and at the worst possible place. We'll need a good dose of ingenuity to save the day.

Some relevant links:

[Bobbias]

The level of techno-wizardry in this series is absolutely insane. Thank you so much for documenting this. It's so rare that you actually get to see something like this.

[_billion_suns]

Nice job guys!!! You probably have fixed a 50 year old “Oh S***” screwup from an Apollo-era test engineer 😂😂

[dogsarebest]

Was waiting for this video. The last video left on such a cliff hanger and I'm usually late to the party!

[colinstu]

12:20 "need to make a pulse like this. with a transformer like this." I love it

[skfalpink]

You guys will need a year long holiday after all this stress! P.S. I wonder if that module was deliberately "fried" so that Nasa could know what the actual failure limits of the system were?

[Maxxarcade]

You guys are such a great team! How did you all meet each other?

[PepijndeVos]

Brilliant! Random question: Why is the AGC all 3-input NAND chips? Seems inefficient. I suppose at least they do use some flip-flops for sequential logic? Do you know which models exactly?

[JakubYTb]

That genius moment when Mike is like: "Could we... replace that guy with a PNP?"

[JamieWhitehorn]

"OK people, listen up. The people upstairs handed us this one and we gotta come through. We gotta find a way to repair this coil assembly, in that potted module, using nothing by the bits in that cabinet." 👍🏻😀✅

[Fake_Blood]

Mike saves the day again! The most brilliant solutions always seems to start when someone says « what if we... » and then there’s a solid 5 seconds of silence from the team.

[eddievhfan]

Marc could be right about the PNP thing—back in those days, PNP transistor fabricator was kinda sucky, and they usually had worse hFE, V_CEmax, you name it. So an all-NPN design may have been considered necessary for reliability.

[dr.strangelove]

Better than an action thriller with more suspense! Excellent work!! I learn new things from you masters and you explain in such a beautiful way👍👍

[charleskillian]

I’m nearly 69 years old. Grew up watching everything from Mercury to Apollo. I ended up having two careers. Spent twenty years as an electronics technician doing board level repairs. Was in a hospital lab late one night and broke a leg off an optometrist-isolator. Customer bet me dinner I couldn’t solder the leg back on. Was a pretty good dinner. Now I sit in front of a computer all day as a systems engineer. Not nearly as much fun.

Oh, for the record, I would have rewound the transformer... just to say it could be done. 🤩

I wish I could come over and just watch.

[guxinim]

Watching this restoration as it unfolds is amazing. It makes the internet worth it again.

[compwiz]

"Apollo Houston, try switching Q11 to PNP"

[alpcns]

Absolutely stunning. This is brilliant engineering - in fact, this is the level of ingenuity and insight that got us on the moon! My hat off - again.

[MJMC]

I don't trust inductors! made me grin :) What a team you are.

[aaronbonner]

I am sad I can only like these videos once each :(

[Ghozer]

I just sat and watched the entire series, then just as I hit the end of the last episode (17) it showed number 18, and I was like WHAT? - Checked and was "uploaded 43 mins ago" - YES!! 1 more before bed, already 8:20am haha!

[BersekViking]

Modern transistors have a much higher bandwiidth then transistors from the 60s and 70s. Using a modern transistor in old designs may cause ringing and oscillations. A capacitor of a few pF between B and C often solves the problem.